[PATCH] D115907: [misexpect] Re-implement MisExpect Diagnostics

[Paul Kirth via Phabricator via cfe-commits]

paulkirth updated this revision to Diff 418025.
paulkirth added a comment.

Add missing GenerateArgs call to propagate flags to the backend outside of cc1


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115907/new/

https://reviews.llvm.org/D115907

Files:
  clang/docs/MisExpect.rst
  clang/docs/ReleaseNotes.rst
  clang/include/clang/Basic/CodeGenOptions.def
  clang/include/clang/Basic/CodeGenOptions.h
  clang/include/clang/Basic/DiagnosticDriverKinds.td
  clang/include/clang/Basic/DiagnosticFrontendKinds.td
  clang/include/clang/Basic/DiagnosticGroups.td
  clang/include/clang/Driver/Options.td
  clang/lib/CodeGen/BackendUtil.cpp
  clang/lib/CodeGen/CodeGenAction.cpp
  clang/lib/Frontend/CompilerInvocation.cpp
  clang/test/Profile/Inputs/misexpect-branch-nonconst-expect-arg.proftext
  clang/test/Profile/Inputs/misexpect-branch.proftext
  clang/test/Profile/Inputs/misexpect-switch-default-only.proftext
  clang/test/Profile/Inputs/misexpect-switch-default.proftext
  clang/test/Profile/Inputs/misexpect-switch-nonconst.proftext
  clang/test/Profile/Inputs/misexpect-switch.proftext
  clang/test/Profile/misexpect-branch-cold.c
  clang/test/Profile/misexpect-branch-nonconst-expected-val.c
  clang/test/Profile/misexpect-branch-unpredictable.c
  clang/test/Profile/misexpect-branch.c
  clang/test/Profile/misexpect-switch-default.c
  clang/test/Profile/misexpect-switch-nonconst.c
  clang/test/Profile/misexpect-switch-only-default-case.c
  clang/test/Profile/misexpect-switch.c
  llvm/docs/MisExpect.rst
  llvm/include/llvm/IR/DiagnosticInfo.h
  llvm/include/llvm/IR/LLVMContext.h
  llvm/include/llvm/Target/TargetOptions.h
  llvm/include/llvm/Transforms/Utils/MisExpect.h
  llvm/lib/IR/DiagnosticInfo.cpp
  llvm/lib/IR/LLVMContext.cpp
  llvm/lib/IR/LLVMContextImpl.h
  llvm/lib/Transforms/IPO/SampleProfile.cpp
  llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
  llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
  llvm/lib/Transforms/Utils/CMakeLists.txt
  llvm/lib/Transforms/Utils/MisExpect.cpp
  llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch-correct.proftext
  llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch-threshold.proftext
  llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch.proftext
  llvm/test/Transforms/PGOProfile/Inputs/misexpect-switch-correct.proftext
  llvm/test/Transforms/PGOProfile/Inputs/misexpect-switch.proftext
  llvm/test/Transforms/PGOProfile/misexpect-branch-correct.ll
  llvm/test/Transforms/PGOProfile/misexpect-branch-stripped.ll
  llvm/test/Transforms/PGOProfile/misexpect-branch-unpredictable.ll
  llvm/test/Transforms/PGOProfile/misexpect-branch.ll
  llvm/test/Transforms/PGOProfile/misexpect-switch-default.ll
  llvm/test/Transforms/PGOProfile/misexpect-switch.ll


Index: llvm/test/Transforms/PGOProfile/misexpect-switch.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/misexpect-switch.ll
@@ -0,0 +1,285 @@
+; Test misexpect diagnostics handle swich statements, and report source locations correctly
+
+; RUN: llvm-profdata merge %S/Inputs/misexpect-switch.proftext -o %t.profdata
+; RUN: llvm-profdata merge %S/Inputs/misexpect-switch-correct.proftext -o %t.c.profdata
+
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -S 2>&1 | FileCheck %s --check-prefix=WARNING
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=REMARK
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=BOTH
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s --check-prefix=DISABLED
+
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.c.profdata -pgo-warn-misexpect -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=CORRECT
+
+; WARNING-DAG: warning: misexpect-switch.c:26:30: 0.00%
+; WARNING-NOT: remark: misexpect-switch.c:26:30: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 8112) of profiled executions.
+
+; REMARK-NOT: warning: misexpect-switch.c:26:30: 0.00%
+; REMARK-DAG: remark: misexpect-switch.c:26:30: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 8112) of profiled executions.
+
+; BOTH-DAG: warning: misexpect-switch.c:26:30: 0.00%
+; BOTH-DAG: remark: misexpect-switch.c:26:30: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 8112) of profiled executions.
+
+; DISABLED-NOT: warning: misexpect-switch.c:26:30: 0.00%
+; DISABLED-NOT: remark: misexpect-switch.c:26:30: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 8112) of profiled executions.
+
+; DISABLED-NOT: warning: misexpect-switch.c:26:30: 0.00%
+; DISABLED-NOT: remark: misexpect-switch.c:26:30: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 8112) of profiled executions.
+
+; CORRECT-NOT: warning: {{.*}}
+; CORRECT-NOT: remark: {{.*}}
+
+
+; ModuleID = 'misexpect-switch.c'
+source_filename = "misexpect-switch.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@inner_loop = dso_local constant i32 1000, align 4, !dbg !0
+@outer_loop = dso_local constant i32 20, align 4, !dbg !6
+@arry_size = dso_local constant i32 25, align 4, !dbg !10
+@arry = dso_local global [25 x i32] zeroinitializer, align 16, !dbg !12
+
+; Function Attrs: nounwind uwtable
+define dso_local void @init_arry() #0 !dbg !21 {
+entry:
+  %i = alloca i32, align 4
+  %0 = bitcast i32* %i to i8*, !dbg !26
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #6, !dbg !26
+  call void @llvm.dbg.declare(metadata i32* %i, metadata !25, metadata !DIExpression()), !dbg !27
+  store i32 0, i32* %i, align 4, !dbg !28, !tbaa !30
+  br label %for.cond, !dbg !34
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %1 = load i32, i32* %i, align 4, !dbg !35, !tbaa !30
+  %cmp = icmp slt i32 %1, 25, !dbg !37
+  br i1 %cmp, label %for.body, label %for.end, !dbg !38
+
+for.body:                                         ; preds = %for.cond
+  %call = call i32 @rand() #6, !dbg !39
+  %rem = srem i32 %call, 10, !dbg !41
+  %2 = load i32, i32* %i, align 4, !dbg !42, !tbaa !30
+  %idxprom = sext i32 %2 to i64, !dbg !43
+  %arrayidx = getelementptr inbounds [25 x i32], [25 x i32]* @arry, i64 0, i64 %idxprom, !dbg !43
+  store i32 %rem, i32* %arrayidx, align 4, !dbg !44, !tbaa !30
+  br label %for.inc, !dbg !45
+
+for.inc:                                          ; preds = %for.body
+  %3 = load i32, i32* %i, align 4, !dbg !46, !tbaa !30
+  %inc = add nsw i32 %3, 1, !dbg !46
+  store i32 %inc, i32* %i, align 4, !dbg !46, !tbaa !30
+  br label %for.cond, !dbg !47, !llvm.loop !48
+
+for.end:                                          ; preds = %for.cond
+  %4 = bitcast i32* %i to i8*, !dbg !50
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %4) #6, !dbg !50
+  ret void, !dbg !50
+}
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #2
+
+; Function Attrs: nounwind
+declare dso_local i32 @rand() #3
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
+
+; Function Attrs: nounwind uwtable
+define dso_local i32 @main() #0 !dbg !51 {
+entry:
+  %retval = alloca i32, align 4
+  %val = alloca i32, align 4
+  %j = alloca i32, align 4
+  %condition = alloca i32, align 4
+  store i32 0, i32* %retval, align 4
+  call void @init_arry(), !dbg !62
+  %0 = bitcast i32* %val to i8*, !dbg !63
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #6, !dbg !63
+  call void @llvm.dbg.declare(metadata i32* %val, metadata !55, metadata !DIExpression()), !dbg !64
+  store i32 0, i32* %val, align 4, !dbg !64, !tbaa !30
+  %1 = bitcast i32* %j to i8*, !dbg !65
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %1) #6, !dbg !65
+  call void @llvm.dbg.declare(metadata i32* %j, metadata !56, metadata !DIExpression()), !dbg !66
+  store i32 0, i32* %j, align 4, !dbg !67, !tbaa !30
+  br label %for.cond, !dbg !68
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %2 = load i32, i32* %j, align 4, !dbg !69, !tbaa !30
+  %cmp = icmp slt i32 %2, 20000, !dbg !70
+  br i1 %cmp, label %for.body, label %for.end, !dbg !71
+
+for.body:                                         ; preds = %for.cond
+  %3 = bitcast i32* %condition to i8*, !dbg !72
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %3) #6, !dbg !72
+  call void @llvm.dbg.declare(metadata i32* %condition, metadata !57, metadata !DIExpression()), !dbg !73
+  %call = call i32 @rand() #6, !dbg !74
+  %rem = srem i32 %call, 5, !dbg !75
+  store i32 %rem, i32* %condition, align 4, !dbg !73, !tbaa !30
+  %4 = load i32, i32* %condition, align 4, !dbg !76, !tbaa !30
+  %conv = zext i32 %4 to i64, !dbg !76
+  %expval = call i64 @llvm.expect.i64(i64 %conv, i64 0), !dbg !77
+  switch i64 %expval, label %sw.default [
+    i64 0, label %sw.bb
+    i64 1, label %sw.bb2
+    i64 2, label %sw.bb2
+    i64 3, label %sw.bb2
+    i64 4, label %sw.bb3
+  ], !dbg !78
+
+sw.bb:                                            ; preds = %for.body
+  %call1 = call i32 @sum(i32* getelementptr inbounds ([25 x i32], [25 x i32]* @arry, i64 0, i64 0), i32 25), !dbg !79
+  %5 = load i32, i32* %val, align 4, !dbg !81, !tbaa !30
+  %add = add nsw i32 %5, %call1, !dbg !81
+  store i32 %add, i32* %val, align 4, !dbg !81, !tbaa !30
+  br label %sw.epilog, !dbg !82
+
+sw.bb2:                                           ; preds = %for.body, %for.body, %for.body
+  br label %sw.epilog, !dbg !83
+
+sw.bb3:                                           ; preds = %for.body
+  %call4 = call i32 @random_sample(i32* getelementptr inbounds ([25 x i32], [25 x i32]* @arry, i64 0, i64 0), i32 25), !dbg !84
+  %6 = load i32, i32* %val, align 4, !dbg !85, !tbaa !30
+  %add5 = add nsw i32 %6, %call4, !dbg !85
+  store i32 %add5, i32* %val, align 4, !dbg !85, !tbaa !30
+  br label %sw.epilog, !dbg !86
+
+sw.default:                                       ; preds = %for.body
+  unreachable, !dbg !87
+
+sw.epilog:                                        ; preds = %sw.bb3, %sw.bb2, %sw.bb
+  %7 = bitcast i32* %condition to i8*, !dbg !88
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %7) #6, !dbg !88
+  br label %for.inc, !dbg !89
+
+for.inc:                                          ; preds = %sw.epilog
+  %8 = load i32, i32* %j, align 4, !dbg !90, !tbaa !30
+  %inc = add nsw i32 %8, 1, !dbg !90
+  store i32 %inc, i32* %j, align 4, !dbg !90, !tbaa !30
+  br label %for.cond, !dbg !91, !llvm.loop !92
+
+for.end:                                          ; preds = %for.cond
+  %9 = bitcast i32* %j to i8*, !dbg !94
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %9) #6, !dbg !94
+  %10 = bitcast i32* %val to i8*, !dbg !94
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %10) #6, !dbg !94
+  ret i32 0, !dbg !95
+}
+
+; Function Attrs: nounwind readnone willreturn
+declare i64 @llvm.expect.i64(i64, i64) #4
+
+declare dso_local i32 @sum(i32*, i32) #5
+
+declare dso_local i32 @random_sample(i32*, i32) #5
+
+attributes #0 = { nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { argmemonly nounwind willreturn }
+attributes #2 = { nounwind readnone speculatable willreturn }
+attributes #3 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #4 = { nounwind readnone willreturn }
+attributes #5 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #6 = { nounwind }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!17, !18, !19}
+!llvm.ident = !{!20}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "inner_loop", scope: !2, file: !3, line: 7, type: !8, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None)
+!3 = !DIFile(filename: "misexpect-switch.c", directory: ".")
+!4 = !{}
+!5 = !{!0, !6, !10, !12}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "outer_loop", scope: !2, file: !3, line: 8, type: !8, isLocal: false, isDefinition: true)
+!8 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !9)
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !DIGlobalVariableExpression(var: !11, expr: !DIExpression())
+!11 = distinct !DIGlobalVariable(name: "arry_size", scope: !2, file: !3, line: 9, type: !8, isLocal: false, isDefinition: true)
+!12 = !DIGlobalVariableExpression(var: !13, expr: !DIExpression())
+!13 = distinct !DIGlobalVariable(name: "arry", scope: !2, file: !3, line: 11, type: !14, isLocal: false, isDefinition: true)
+!14 = !DICompositeType(tag: DW_TAG_array_type, baseType: !9, size: 800, elements: !15)
+!15 = !{!16}
+!16 = !DISubrange(count: 25)
+!17 = !{i32 2, !"Dwarf Version", i32 4}
+!18 = !{i32 2, !"Debug Info Version", i32 3}
+!19 = !{i32 1, !"wchar_size", i32 4}
+!20 = !{!"clang version 10.0.0"}
+!21 = distinct !DISubprogram(name: "init_arry", scope: !3, file: !3, line: 13, type: !22, scopeLine: 13, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !24)
+!22 = !DISubroutineType(types: !23)
+!23 = !{null}
+!24 = !{!25}
+!25 = !DILocalVariable(name: "i", scope: !21, file: !3, line: 14, type: !9)
+!26 = !DILocation(line: 14, column: 3, scope: !21)
+!27 = !DILocation(line: 14, column: 7, scope: !21)
+!28 = !DILocation(line: 15, column: 10, scope: !29)
+!29 = distinct !DILexicalBlock(scope: !21, file: !3, line: 15, column: 3)
+!30 = !{!31, !31, i64 0}
+!31 = !{!"int", !32, i64 0}
+!32 = !{!"omnipotent char", !33, i64 0}
+!33 = !{!"Simple C/C++ TBAA"}
+!34 = !DILocation(line: 15, column: 8, scope: !29)
+!35 = !DILocation(line: 15, column: 15, scope: !36)
+!36 = distinct !DILexicalBlock(scope: !29, file: !3, line: 15, column: 3)
+!37 = !DILocation(line: 15, column: 17, scope: !36)
+!38 = !DILocation(line: 15, column: 3, scope: !29)
+!39 = !DILocation(line: 16, column: 15, scope: !40)
+!40 = distinct !DILexicalBlock(scope: !36, file: !3, line: 15, column: 35)
+!41 = !DILocation(line: 16, column: 22, scope: !40)
+!42 = !DILocation(line: 16, column: 10, scope: !40)
+!43 = !DILocation(line: 16, column: 5, scope: !40)
+!44 = !DILocation(line: 16, column: 13, scope: !40)
+!45 = !DILocation(line: 17, column: 3, scope: !40)
+!46 = !DILocation(line: 15, column: 30, scope: !36)
+!47 = !DILocation(line: 15, column: 3, scope: !36)
+!48 = distinct !{!48, !38, !49}
+!49 = !DILocation(line: 17, column: 3, scope: !29)
+!50 = !DILocation(line: 18, column: 1, scope: !21)
+!51 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 20, type: !52, scopeLine: 20, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !54)
+!52 = !DISubroutineType(types: !53)
+!53 = !{!9}
+!54 = !{!55, !56, !57}
+!55 = !DILocalVariable(name: "val", scope: !51, file: !3, line: 22, type: !9)
+!56 = !DILocalVariable(name: "j", scope: !51, file: !3, line: 23, type: !9)
+!57 = !DILocalVariable(name: "condition", scope: !58, file: !3, line: 25, type: !61)
+!58 = distinct !DILexicalBlock(scope: !59, file: !3, line: 24, column: 49)
+!59 = distinct !DILexicalBlock(scope: !60, file: !3, line: 24, column: 3)
+!60 = distinct !DILexicalBlock(scope: !51, file: !3, line: 24, column: 3)
+!61 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!62 = !DILocation(line: 21, column: 3, scope: !51)
+!63 = !DILocation(line: 22, column: 3, scope: !51)
+!64 = !DILocation(line: 22, column: 7, scope: !51)
+!65 = !DILocation(line: 23, column: 3, scope: !51)
+!66 = !DILocation(line: 23, column: 7, scope: !51)
+!67 = !DILocation(line: 24, column: 10, scope: !60)
+!68 = !DILocation(line: 24, column: 8, scope: !60)
+!69 = !DILocation(line: 24, column: 15, scope: !59)
+!70 = !DILocation(line: 24, column: 17, scope: !59)
+!71 = !DILocation(line: 24, column: 3, scope: !60)
+!72 = !DILocation(line: 25, column: 5, scope: !58)
+!73 = !DILocation(line: 25, column: 14, scope: !58)
+!74 = !DILocation(line: 25, column: 26, scope: !58)
+!75 = !DILocation(line: 25, column: 33, scope: !58)
+!76 = !DILocation(line: 26, column: 30, scope: !58)
+!77 = !DILocation(line: 26, column: 13, scope: !58)
+!78 = !DILocation(line: 26, column: 5, scope: !58)
+!79 = !DILocation(line: 28, column: 14, scope: !80)
+!80 = distinct !DILexicalBlock(scope: !58, file: !3, line: 26, column: 45)
+!81 = !DILocation(line: 28, column: 11, scope: !80)
+!82 = !DILocation(line: 29, column: 7, scope: !80)
+!83 = !DILocation(line: 33, column: 7, scope: !80)
+!84 = !DILocation(line: 35, column: 14, scope: !80)
+!85 = !DILocation(line: 35, column: 11, scope: !80)
+!86 = !DILocation(line: 36, column: 7, scope: !80)
+!87 = !DILocation(line: 38, column: 7, scope: !80)
+!88 = !DILocation(line: 40, column: 3, scope: !59)
+!89 = !DILocation(line: 40, column: 3, scope: !58)
+!90 = !DILocation(line: 24, column: 44, scope: !59)
+!91 = !DILocation(line: 24, column: 3, scope: !59)
+!92 = distinct !{!92, !71, !93}
+!93 = !DILocation(line: 40, column: 3, scope: !60)
+!94 = !DILocation(line: 43, column: 1, scope: !51)
+!95 = !DILocation(line: 42, column: 3, scope: !51)
Index: llvm/test/Transforms/PGOProfile/misexpect-switch-default.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/misexpect-switch-default.ll
@@ -0,0 +1,189 @@
+; Test misexpect handles switch statements when debug information is stripped
+
+; RUN: llvm-profdata merge %S/Inputs/misexpect-switch.proftext -o %t.profdata
+
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -S 2>&1 | FileCheck %s --check-prefix=WARNING
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=REMARK
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=BOTH
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s --check-prefix=DISABLED
+
+; WARNING-DAG: warning: <unknown>:0:0: 0.00%
+; WARNING-NOT: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 27943) of profiled executions.
+
+; REMARK-NOT: warning: <unknown>:0:0: 0.00%
+; REMARK-DAG: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 27943) of profiled executions.
+
+; BOTH-DAG: warning: <unknown>:0:0: 0.00%
+; BOTH-DAG: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 27943) of profiled executions.
+
+; DISABLED-NOT: warning: <unknown>:0:0: 0.00%
+; DISABLED-NOT: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 27943) of profiled executions.
+
+; DISABLED-NOT: warning: <unknown>:0:0: 0.00%
+; DISABLED-NOT: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 0.00% (0 / 27943) of profiled executions.
+
+; CORRECT-NOT: warning: {{.*}}
+; CORRECT-NOT: remark: {{.*}}
+
+
+; ModuleID = 'misexpect-switch.c'
+source_filename = "misexpect-switch.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@inner_loop = dso_local constant i32 1000, align 4
+@outer_loop = dso_local constant i32 20, align 4
+@arry_size = dso_local constant i32 25, align 4
+@arry = dso_local global [25 x i32] zeroinitializer, align 16
+
+; Function Attrs: nounwind uwtable
+define dso_local void @init_arry() #0 {
+entry:
+  %i = alloca i32, align 4
+  %0 = bitcast i32* %i to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #6
+  store i32 0, i32* %i, align 4, !tbaa !4
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %1 = load i32, i32* %i, align 4, !tbaa !4
+  %cmp = icmp slt i32 %1, 25
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %call = call i32 @rand() #6
+  %rem = srem i32 %call, 10
+  %2 = load i32, i32* %i, align 4, !tbaa !4
+  %idxprom = sext i32 %2 to i64
+  %arrayidx = getelementptr inbounds [25 x i32], [25 x i32]* @arry, i64 0, i64 %idxprom
+  store i32 %rem, i32* %arrayidx, align 4, !tbaa !4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body
+  %3 = load i32, i32* %i, align 4, !tbaa !4
+  %inc = add nsw i32 %3, 1
+  store i32 %inc, i32* %i, align 4, !tbaa !4
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  %4 = bitcast i32* %i to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %4) #6
+  ret void
+}
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #2
+
+; Function Attrs: nounwind
+declare dso_local i32 @rand() #3
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
+
+; Function Attrs: nounwind uwtable
+define dso_local i32 @main() #0 {
+entry:
+  %retval = alloca i32, align 4
+  %val = alloca i32, align 4
+  %j = alloca i32, align 4
+  %condition = alloca i32, align 4
+  store i32 0, i32* %retval, align 4
+  call void @init_arry()
+  %0 = bitcast i32* %val to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #6
+  store i32 0, i32* %val, align 4, !tbaa !4
+  %1 = bitcast i32* %j to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %1) #6
+  store i32 0, i32* %j, align 4, !tbaa !4
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %2 = load i32, i32* %j, align 4, !tbaa !4
+  %cmp = icmp slt i32 %2, 20000
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %3 = bitcast i32* %condition to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %3) #6
+  %call = call i32 @rand() #6
+  %rem = srem i32 %call, 5
+  store i32 %rem, i32* %condition, align 4, !tbaa !4
+  %4 = load i32, i32* %condition, align 4, !tbaa !4
+  %conv = zext i32 %4 to i64
+  %expval = call i64 @llvm.expect.i64(i64 %conv, i64 6)
+  switch i64 %expval, label %sw.default [
+    i64 0, label %sw.bb
+    i64 1, label %sw.bb2
+    i64 2, label %sw.bb2
+    i64 3, label %sw.bb2
+    i64 4, label %sw.bb3
+  ]
+
+sw.bb:                                            ; preds = %for.body
+  %call1 = call i32 @sum(i32* getelementptr inbounds ([25 x i32], [25 x i32]* @arry, i64 0, i64 0), i32 25)
+  %5 = load i32, i32* %val, align 4, !tbaa !4
+  %add = add nsw i32 %5, %call1
+  store i32 %add, i32* %val, align 4, !tbaa !4
+  br label %sw.epilog
+
+sw.bb2:                                           ; preds = %for.body, %for.body, %for.body
+  br label %sw.epilog
+
+sw.bb3:                                           ; preds = %for.body
+  %call4 = call i32 @random_sample(i32* getelementptr inbounds ([25 x i32], [25 x i32]* @arry, i64 0, i64 0), i32 25)
+  %6 = load i32, i32* %val, align 4, !tbaa !4
+  %add5 = add nsw i32 %6, %call4
+  store i32 %add5, i32* %val, align 4, !tbaa !4
+  br label %sw.epilog
+
+sw.default:                                       ; preds = %for.body
+  unreachable
+
+sw.epilog:                                        ; preds = %sw.bb3, %sw.bb2, %sw.bb
+  %7 = bitcast i32* %condition to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %7) #6
+  br label %for.inc
+
+for.inc:                                          ; preds = %sw.epilog
+  %8 = load i32, i32* %j, align 4, !tbaa !4
+  %inc = add nsw i32 %8, 1
+  store i32 %inc, i32* %j, align 4, !tbaa !4
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  %9 = bitcast i32* %j to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %9) #6
+  %10 = bitcast i32* %val to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %10) #6
+  ret i32 0
+}
+
+; Function Attrs: nounwind readnone willreturn
+declare i64 @llvm.expect.i64(i64, i64) #4
+
+declare dso_local i32 @sum(i32*, i32) #5
+
+declare dso_local i32 @random_sample(i32*, i32) #5
+
+attributes #0 = { nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { argmemonly nounwind willreturn }
+attributes #2 = { nounwind readnone speculatable willreturn }
+attributes #3 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #4 = { nounwind readnone willreturn }
+attributes #5 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #6 = { nounwind }
+
+!llvm.module.flags = !{!0, !1, !2}
+!llvm.ident = !{!3}
+
+!0 = !{i32 2, !"Dwarf Version", i32 4}
+!1 = !{i32 2, !"Debug Info Version", i32 3}
+!2 = !{i32 1, !"wchar_size", i32 4}
+!3 = !{!"clang version 10.0.0 (60b79b85b1763d3d25630261e5cd1adb7f0835bc)"}
+!4 = !{!5, !5, i64 0}
+!5 = !{!"int", !6, i64 0}
+!6 = !{!"omnipotent char", !7, i64 0}
+!7 = !{!"Simple C/C++ TBAA"}
Index: llvm/test/Transforms/PGOProfile/misexpect-branch.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/misexpect-branch.ll
@@ -0,0 +1,124 @@
+; Test that misexpect diagnostics are emtted when profile branch weights are
+; below the branch weights added by llvm.expect intrinsics
+
+; RUN: llvm-profdata merge %S/Inputs/misexpect-branch.proftext -o %t.profdata
+
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -S 2>&1 | FileCheck %s --check-prefix=WARNING
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=REMARK
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=BOTH
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s --check-prefix=DISABLED
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -misexpect-tolerance=81 -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=THRESHOLD
+
+; WARNING-DAG: warning: misexpect-branch.c:22:0: 19.98%
+; WARNING-NOT: remark: misexpect-branch.c:22:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+; REMARK-NOT: warning: misexpect-branch.c:22:0: 19.98%
+; REMARK-DAG: remark: misexpect-branch.c:22:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+; BOTH-DAG: warning: misexpect-branch.c:22:0: 19.98%
+; BOTH-DAG: remark: misexpect-branch.c:22:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+; DISABLED-NOT: warning: misexpect-branch.c:22:0: 19.98%
+; DISABLED-NOT: remark: misexpect-branch.c:22:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+; THRESHOLD-NOT: warning: misexpect-branch.c:22:0: 19.98%
+; THRESHOLD-NOT: remark: misexpect-branch.c:22:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+
+; ModuleID = 'misexpect-branch.c'
+source_filename = "misexpect-branch.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@inner_loop = constant i32 100, align 4
+@outer_loop = constant i32 2000, align 4
+
+; Function Attrs: nounwind
+define i32 @bar() #0 !dbg !6 {
+entry:
+  %rando = alloca i32, align 4
+  %x = alloca i32, align 4
+  %0 = bitcast i32* %rando to i8*, !dbg !9
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #4, !dbg !9
+  %call = call i32 (...) @buzz(), !dbg !9
+  store i32 %call, i32* %rando, align 4, !dbg !9, !tbaa !10
+  %1 = bitcast i32* %x to i8*, !dbg !14
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %1) #4, !dbg !14
+  store i32 0, i32* %x, align 4, !dbg !14, !tbaa !10
+  %2 = load i32, i32* %rando, align 4, !dbg !15, !tbaa !10
+  %rem = srem i32 %2, 200000, !dbg !15
+  %cmp = icmp eq i32 %rem, 0, !dbg !15
+  %lnot = xor i1 %cmp, true, !dbg !15
+  %lnot1 = xor i1 %lnot, true, !dbg !15
+  %lnot.ext = zext i1 %lnot1 to i32, !dbg !15
+  %conv = sext i32 %lnot.ext to i64, !dbg !15
+  %expval = call i64 @llvm.expect.i64(i64 %conv, i64 1), !dbg !15
+  %tobool = icmp ne i64 %expval, 0, !dbg !15
+  br i1 %tobool, label %if.then, label %if.else, !dbg !15
+
+if.then:                                          ; preds = %entry
+  %3 = load i32, i32* %rando, align 4, !dbg !16, !tbaa !10
+  %call2 = call i32 @baz(i32 %3), !dbg !16
+  store i32 %call2, i32* %x, align 4, !dbg !16, !tbaa !10
+  br label %if.end, !dbg !17
+
+if.else:                                          ; preds = %entry
+  %call3 = call i32 @foo(i32 50), !dbg !18
+  store i32 %call3, i32* %x, align 4, !dbg !18, !tbaa !10
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  %4 = load i32, i32* %x, align 4, !dbg !19, !tbaa !10
+  %5 = bitcast i32* %x to i8*, !dbg !20
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %5) #4, !dbg !20
+  %6 = bitcast i32* %rando to i8*, !dbg !20
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %6) #4, !dbg !20
+  ret i32 %4, !dbg !19
+}
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
+
+declare i32 @buzz(...) #2
+
+; Function Attrs: nounwind readnone willreturn
+declare i64 @llvm.expect.i64(i64, i64) #3
+
+declare i32 @baz(i32) #2
+
+declare i32 @foo(i32) #2
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { argmemonly nounwind willreturn }
+attributes #2 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #3 = { nounwind readnone willreturn }
+attributes #4 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 (trunk c20270bfffc9d6965219de339d66c61e9fe7d82d)", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "<stdin>", directory: ".")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{!"clang version 10.0.0 (trunk c20270bfffc9d6965219de339d66c61e9fe7d82d)"}
+!6 = distinct !DISubprogram(name: "bar", scope: !7, file: !7, line: 19, type: !8, scopeLine: 19, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!7 = !DIFile(filename: "misexpect-branch.c", directory: ".")
+!8 = !DISubroutineType(types: !2)
+!9 = !DILocation(line: 20, scope: !6)
+!10 = !{!11, !11, i64 0}
+!11 = !{!"int", !12, i64 0}
+!12 = !{!"omnipotent char", !13, i64 0}
+!13 = !{!"Simple C/C++ TBAA"}
+!14 = !DILocation(line: 21, scope: !6)
+!15 = !DILocation(line: 22, scope: !6)
+!16 = !DILocation(line: 23, scope: !6)
+!17 = !DILocation(line: 24, scope: !6)
+!18 = !DILocation(line: 25, scope: !6)
+!19 = !DILocation(line: 27, scope: !6)
+!20 = !DILocation(line: 28, scope: !6)
Index: llvm/test/Transforms/PGOProfile/misexpect-branch-unpredictable.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/misexpect-branch-unpredictable.ll
@@ -0,0 +1,87 @@
+; Test misexpect doesn't issue diagnostics when a branch is marked unpredictable
+
+; RUN: llvm-profdata merge %S/Inputs/misexpect-branch-correct.proftext -o %t.profdata
+
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -pass-remarks=misexpect -S  2>&1 | FileCheck %s
+
+; CHECK-NOT: warning: {{.*}}
+; CHECK-NOT: remark: {{.*}}
+
+
+; ModuleID = 'misexpect-branch-unpredictable.c'
+source_filename = "clang/test/Profile/misexpect-branch-unpredictable.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@inner_loop = constant i32 100, align 4
+@outer_loop = constant i32 2000, align 4
+
+; Function Attrs: nounwind
+define i32 @bar() #0 {
+entry:
+  %rando = alloca i32, align 4
+  %x = alloca i32, align 4
+  %0 = bitcast i32* %rando to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #3
+  %call = call i32 (...) @buzz()
+  store i32 %call, i32* %rando, align 4, !tbaa !2
+  %1 = bitcast i32* %x to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %1) #3
+  store i32 0, i32* %x, align 4, !tbaa !2
+  %2 = load i32, i32* %rando, align 4, !tbaa !2
+  %rem = srem i32 %2, 200000
+  %cmp = icmp eq i32 %rem, 0
+  %lnot = xor i1 %cmp, true
+  %lnot1 = xor i1 %lnot, true
+  %lnot.ext = zext i1 %lnot1 to i32
+  %conv = sext i32 %lnot.ext to i64
+  %tobool = icmp ne i64 %conv, 0
+  br i1 %tobool, label %if.then, label %if.else, !unpredictable !6
+
+if.then:                                          ; preds = %entry
+  %3 = load i32, i32* %rando, align 4, !tbaa !2
+  %call2 = call i32 @baz(i32 %3)
+  store i32 %call2, i32* %x, align 4, !tbaa !2
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  %call3 = call i32 @foo(i32 50)
+  store i32 %call3, i32* %x, align 4, !tbaa !2
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  %4 = load i32, i32* %x, align 4, !tbaa !2
+  %5 = bitcast i32* %x to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %5) #3
+  %6 = bitcast i32* %rando to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %6) #3
+  ret i32 %4
+}
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
+
+declare i32 @buzz(...) #2
+
+declare i32 @baz(i32) #2
+
+declare i32 @foo(i32) #2
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { argmemonly nounwind willreturn }
+attributes #2 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #3 = { nounwind }
+
+!llvm.module.flags = !{!0}
+!llvm.ident = !{!1}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{!"Fuchsia clang version 10.0.0 (153b453014c94291c8c6cf6320b2f46df40f26f3) (based on LLVM 10.0.0svn)"}
+!2 = !{!3, !3, i64 0}
+!3 = !{!"int", !4, i64 0}
+!4 = !{!"omnipotent char", !5, i64 0}
+!5 = !{!"Simple C/C++ TBAA"}
+!6 = !{}
Index: llvm/test/Transforms/PGOProfile/misexpect-branch-stripped.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/misexpect-branch-stripped.ll
@@ -0,0 +1,104 @@
+; Test that misexpect diagnostics handle stripped debug info gracefully
+
+; RUN: llvm-profdata merge %S/Inputs/misexpect-branch.proftext -o %t.profdata
+
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -S 2>&1 | FileCheck %s --check-prefix=WARNING
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=REMARK
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -pass-remarks=misexpect -S 2>&1 | FileCheck %s --check-prefix=BOTH
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s --check-prefix=DISABLED
+
+; WARNING-DAG: warning: <unknown>:0:0: 19.98%
+; WARNING-NOT: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+; REMARK-NOT: warning: <unknown>:0:0: 19.98%
+; REMARK-DAG: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+; BOTH-DAG: warning: <unknown>:0:0: 19.98%
+; BOTH-DAG: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+; DISABLED-NOT: warning: <unknown>:0:0: 19.98%
+; DISABLED-NOT: remark: <unknown>:0:0: Potential performance regression from use of the llvm.expect intrinsic: Annotation was correct on 19.98% (399668 / 2000000) of profiled executions.
+
+
+; ModuleID = 'misexpect-branch.c'
+source_filename = "misexpect-branch.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@inner_loop = constant i32 100, align 4
+@outer_loop = constant i32 2000, align 4
+
+; Function Attrs: nounwind
+define i32 @bar() #0 {
+entry:
+  %rando = alloca i32, align 4
+  %x = alloca i32, align 4
+  %0 = bitcast i32* %rando to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #4
+  %call = call i32 (...) @buzz()
+  store i32 %call, i32* %rando, align 4, !tbaa !3
+  %1 = bitcast i32* %x to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %1) #4
+  store i32 0, i32* %x, align 4, !tbaa !3
+  %2 = load i32, i32* %rando, align 4, !tbaa !3
+  %rem = srem i32 %2, 200000
+  %cmp = icmp eq i32 %rem, 0
+  %lnot = xor i1 %cmp, true
+  %lnot1 = xor i1 %lnot, true
+  %lnot.ext = zext i1 %lnot1 to i32
+  %conv = sext i32 %lnot.ext to i64
+  %expval = call i64 @llvm.expect.i64(i64 %conv, i64 1)
+  %tobool = icmp ne i64 %expval, 0
+  br i1 %tobool, label %if.then, label %if.else
+
+if.then:                                          ; preds = %entry
+  %3 = load i32, i32* %rando, align 4, !tbaa !3
+  %call2 = call i32 @baz(i32 %3)
+  store i32 %call2, i32* %x, align 4, !tbaa !3
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  %call3 = call i32 @foo(i32 50)
+  store i32 %call3, i32* %x, align 4, !tbaa !3
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  %4 = load i32, i32* %x, align 4, !tbaa !3
+  %5 = bitcast i32* %x to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %5) #4
+  %6 = bitcast i32* %rando to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %6) #4
+  ret i32 %4
+}
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
+
+declare i32 @buzz(...) #2
+
+; Function Attrs: nounwind readnone willreturn
+declare i64 @llvm.expect.i64(i64, i64) #3
+
+declare i32 @baz(i32) #2
+
+declare i32 @foo(i32) #2
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { argmemonly nounwind willreturn }
+attributes #2 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #3 = { nounwind readnone willreturn }
+attributes #4 = { nounwind }
+
+!llvm.module.flags = !{!0, !1}
+!llvm.ident = !{!2}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = !{i32 1, !"wchar_size", i32 4}
+!2 = !{!"clang version 10.0.0 (trunk c20270bfffc9d6965219de339d66c61e9fe7d82d)"}
+!3 = !{!4, !4, i64 0}
+!4 = !{!"int", !5, i64 0}
+!5 = !{!"omnipotent char", !6, i64 0}
+!6 = !{!"Simple C/C++ TBAA"}
Index: llvm/test/Transforms/PGOProfile/misexpect-branch-correct.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/misexpect-branch-correct.ll
@@ -0,0 +1,94 @@
+; Test misexpect checks do not issue diagnostics when profiling weights and
+; branch weights added by llvm.expect agree
+
+; RUN: llvm-profdata merge %S/Inputs/misexpect-branch-correct.proftext -o %t.profdata
+
+; RUN: opt < %s -passes="function(lower-expect),pgo-instr-use" -pgo-test-profile-file=%t.profdata -pgo-warn-misexpect -pass-remarks=misexpect -S  2>&1 | FileCheck %s
+
+; CHECK-NOT: warning: {{.*}}
+; CHECK-NOT: remark: {{.*}}
+; CHECK: !{!"branch_weights", i32 0, i32 200000}
+
+
+; ModuleID = 'misexpect-branch-correct.c'
+source_filename = "misexpect-branch-correct.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@inner_loop = constant i32 100, align 4
+@outer_loop = constant i32 2000, align 4
+
+; Function Attrs: nounwind
+define i32 @bar() #0 {
+entry:
+  %rando = alloca i32, align 4
+  %x = alloca i32, align 4
+  %0 = bitcast i32* %rando to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #4
+  %call = call i32 (...) @buzz()
+  store i32 %call, i32* %rando, align 4, !tbaa !3
+  %1 = bitcast i32* %x to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %1) #4
+  store i32 0, i32* %x, align 4, !tbaa !3
+  %2 = load i32, i32* %rando, align 4, !tbaa !3
+  %rem = srem i32 %2, 200000
+  %cmp = icmp eq i32 %rem, 0
+  %lnot = xor i1 %cmp, true
+  %lnot1 = xor i1 %lnot, true
+  %lnot.ext = zext i1 %lnot1 to i32
+  %conv = sext i32 %lnot.ext to i64
+  %expval = call i64 @llvm.expect.i64(i64 %conv, i64 0)
+  %tobool = icmp ne i64 %expval, 0
+  br i1 %tobool, label %if.then, label %if.else
+
+if.then:                                          ; preds = %entry
+  %3 = load i32, i32* %rando, align 4, !tbaa !3
+  %call2 = call i32 @baz(i32 %3)
+  store i32 %call2, i32* %x, align 4, !tbaa !3
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  %call3 = call i32 @foo(i32 50)
+  store i32 %call3, i32* %x, align 4, !tbaa !3
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  %4 = load i32, i32* %x, align 4, !tbaa !3
+  %5 = bitcast i32* %x to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %5) #4
+  %6 = bitcast i32* %rando to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %6) #4
+  ret i32 %4
+}
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
+
+declare i32 @buzz(...) #2
+
+; Function Attrs: nounwind readnone willreturn
+declare i64 @llvm.expect.i64(i64, i64) #3
+
+declare i32 @baz(i32) #2
+
+declare i32 @foo(i32) #2
+
+; Function Attrs: argmemonly nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { argmemonly nounwind willreturn }
+attributes #2 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #3 = { nounwind readnone willreturn }
+attributes #4 = { nounwind }
+
+!llvm.module.flags = !{!0, !1}
+!llvm.ident = !{!2}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = !{i32 1, !"wchar_size", i32 4}
+!2 = !{!"clang version 10.0.0 (c20270bfffc9d6965219de339d66c61e9fe7d82d)"}
+!3 = !{!4, !4, i64 0}
+!4 = !{!"int", !5, i64 0}
+!5 = !{!"omnipotent char", !6, i64 0}
+!6 = !{!"Simple C/C++ TBAA"}
Index: llvm/test/Transforms/PGOProfile/Inputs/misexpect-switch.proftext
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/Inputs/misexpect-switch.proftext
@@ -0,0 +1,15 @@
+# IR level Instrumentation Flag
+:ir
+main
+# Func Hash:
+391331300939170156
+# Num Counters:
+7
+# Counter Values:
+3973
+3970
+0
+11889
+8111
+1
+0
Index: llvm/test/Transforms/PGOProfile/Inputs/misexpect-switch-correct.proftext
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/Inputs/misexpect-switch-correct.proftext
@@ -0,0 +1,15 @@
+# IR level Instrumentation Flag
+:ir
+main
+# Func Hash:
+391331300939170156
+# Num Counters:
+7
+# Counter Values:
+0
+0
+20000
+0
+0
+1
+0
Index: llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch.proftext
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch.proftext
@@ -0,0 +1,38 @@
+# IR level Instrumentation Flag
+:ir
+bar
+# Func Hash:
+146835647075900052
+# Num Counters:
+2
+# Counter Values:
+399668
+1600332
+
+baz
+# Func Hash:
+12884901887
+# Num Counters:
+1
+# Counter Values:
+399668
+
+foo
+# Func Hash:
+29212902728
+# Num Counters:
+2
+# Counter Values:
+40803991
+1600332
+
+main
+# Func Hash:
+41605652536
+# Num Counters:
+3
+# Counter Values:
+2000000
+2000
+1
+
Index: llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch-threshold.proftext
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch-threshold.proftext
@@ -0,0 +1,38 @@
+# IR level Instrumentation Flag
+:ir
+bar
+# Func Hash:
+146835647075900052
+# Num Counters:
+2
+# Counter Values:
+100
+10
+
+baz
+# Func Hash:
+12884901887
+# Num Counters:
+1
+# Counter Values:
+399668
+
+foo
+# Func Hash:
+29212902728
+# Num Counters:
+2
+# Counter Values:
+40803991
+1600332
+
+main
+# Func Hash:
+41605652536
+# Num Counters:
+3
+# Counter Values:
+2000000
+2000
+1
+
Index: llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch-correct.proftext
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PGOProfile/Inputs/misexpect-branch-correct.proftext
@@ -0,0 +1,38 @@
+# IR level Instrumentation Flag
+:ir
+bar
+# Func Hash:
+146835647075900052
+# Num Counters:
+2
+# Counter Values:
+200000
+0
+
+baz
+# Func Hash:
+12884901887
+# Num Counters:
+1
+# Counter Values:
+399668
+
+foo
+# Func Hash:
+29212902728
+# Num Counters:
+2
+# Counter Values:
+40803991
+1600332
+
+main
+# Func Hash:
+41605652536
+# Num Counters:
+3
+# Counter Values:
+2000000
+2000
+1
+
Index: llvm/lib/Transforms/Utils/MisExpect.cpp
===================================================================
--- /dev/null
+++ llvm/lib/Transforms/Utils/MisExpect.cpp
@@ -0,0 +1,234 @@
+//===--- MisExpect.cpp - Check the use of llvm.expect with PGO data -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This contains code to emit warnings for potentially incorrect usage of the
+// llvm.expect intrinsic. This utility extracts the threshold values from
+// metadata associated with the instrumented Branch or Switch instruction. The
+// threshold values are then used to determine if a warning should be emmited.
+//
+// MisExpect's implementation relies on two assumptions about how branch weights
+// are managed in LLVM.
+//
+// 1) Frontend profiling weights are always in place before llvm.expect is
+// lowered in LowerExpectIntrinsic.cpp. Frontend based instrumentation therefore
+// needs to extract the branch weights and then compare them to the weights
+// being added by the llvm.expect intrinsic lowering.
+//
+// 2) Sampling and IR based profiles will *only* have branch weight metadata
+// before profiling data is consulted if they are from a lowered llvm.expect
+// intrinsic. These profiles thus always extract the expected weights and then
+// compare them to the weights collected during profiling to determine if a
+// diagnostic message is warranted.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/MisExpect.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/Analysis/OptimizationRemarkEmitter.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/Support/BranchProbability.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/FormatVariadic.h"
+#include <cstdint>
+#include <functional>
+#include <numeric>
+
+#define DEBUG_TYPE "misexpect"
+
+using namespace llvm;
+using namespace misexpect;
+
+namespace llvm {
+
+// Command line option to enable/disable the warning when profile data suggests
+// a mismatch with the use of the llvm.expect intrinsic
+static cl::opt<bool> PGOWarnMisExpect(
+    "pgo-warn-misexpect", cl::init(false), cl::Hidden,
+    cl::desc("Use this option to turn on/off "
+             "warnings about incorrect usage of llvm.expect intrinsics."));
+
+static cl::opt<unsigned> MisExpectTolerance(
+    "misexpect-tolerance", cl::init(0),
+    cl::desc("Prevents emiting diagnostics when profile counts are "
+             "within N% of the threshold.."));
+
+} // namespace llvm
+
+namespace {
+
+bool isMisExpectDiagEnabled(LLVMContext &Ctx) {
+  return PGOWarnMisExpect || Ctx.getMisExpectWarningRequested();
+}
+
+uint64_t getMisExpectTolerance(LLVMContext &Ctx) {
+  return std::max(static_cast<uint64_t>(MisExpectTolerance),
+                  Ctx.getDiagnosticsMisExpectTolerance());
+}
+
+Instruction *getInstCondition(Instruction *I) {
+  assert(I != nullptr && "MisExpect target Instruction cannot be nullptr");
+  Instruction *Ret = nullptr;
+  if (auto *B = dyn_cast<BranchInst>(I)) {
+    Ret = dyn_cast<Instruction>(B->getCondition());
+  }
+  // TODO: Find a way to resolve condition location for switches
+  // Using the condition of the switch seems to often resolve to an earlier
+  // point in the program, i.e. the calculation of the switch condition, rather
+  // than the switch's location in the source code. Thus, we should use the
+  // instruction to get source code locations rather than the condition to
+  // improve diagnostic output, such as the caret. If the same problem exists
+  // for branch instructions, then we should remove this function and directly
+  // use the instruction
+  //
+  else if (auto *S = dyn_cast<SwitchInst>(I)) {
+    Ret = dyn_cast<Instruction>(S->getCondition());
+  }
+  return Ret ? Ret : I;
+}
+
+void emitMisexpectDiagnostic(Instruction *I, LLVMContext &Ctx,
+                             uint64_t ProfCount, uint64_t TotalCount) {
+  double PercentageCorrect = (double)ProfCount / TotalCount;
+  auto PerString =
+      formatv("{0:P} ({1} / {2})", PercentageCorrect, ProfCount, TotalCount);
+  auto RemStr = formatv(
+      "Potential performance regression from use of the llvm.expect intrinsic: "
+      "Annotation was correct on {0} of profiled executions.",
+      PerString);
+  Twine Msg(PerString);
+  Instruction *Cond = getInstCondition(I);
+  if (isMisExpectDiagEnabled(Ctx))
+    Ctx.diagnose(DiagnosticInfoMisExpect(Cond, Msg));
+  OptimizationRemarkEmitter ORE(I->getParent()->getParent());
+  ORE.emit(OptimizationRemark(DEBUG_TYPE, "misexpect", Cond) << RemStr.str());
+}
+
+} // namespace
+
+namespace llvm {
+namespace misexpect {
+
+// Helper function to extract branch weights into a vector
+Optional<SmallVector<uint32_t, 4>> extractWeights(Instruction *I,
+                                                  LLVMContext &Ctx) {
+  assert(I && "MisExpect::extractWeights given invalid pointer");
+
+  auto *ProfileData = I->getMetadata(LLVMContext::MD_prof);
+  if (!ProfileData)
+    return None;
+
+  unsigned NOps = ProfileData->getNumOperands();
+  if (NOps < 3)
+    return None;
+
+  auto *ProfDataName = dyn_cast<MDString>(ProfileData->getOperand(0));
+  if (!ProfDataName || !ProfDataName->getString().equals("branch_weights"))
+    return None;
+
+  SmallVector<uint32_t, 4> Weights(NOps - 1);
+  for (unsigned Idx = 1; Idx < NOps; Idx++) {
+    ConstantInt *Value =
+        mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(Idx));
+    uint32_t V = Value->getZExtValue();
+    Weights[Idx - 1] = V;
+  }
+
+  return Weights;
+}
+
+void verifyMisExpect(Instruction &I, ArrayRef<uint32_t> RealWeights,
+                     ArrayRef<uint32_t> ExpectedWeights) {
+  // To determine if we emit a diagnostic, we need to compare the branch weights
+  // from the profile to those added by the llvm.expect intrinsic.
+  // So first, we extract the "likely" and "unlikely" weights from
+  // ExpectedWeights And determine the correct weight in the profile to compare
+  // against.
+  uint64_t LikelyBranchWeight = 0,
+           UnlikelyBranchWeight = std::numeric_limits<uint32_t>::max();
+  size_t MaxIndex = 0;
+  for (size_t Idx = 0, End = ExpectedWeights.size(); Idx < End; Idx++) {
+    uint32_t V = ExpectedWeights[Idx];
+    if (LikelyBranchWeight < V) {
+      LikelyBranchWeight = V;
+      MaxIndex = Idx;
+    }
+    if (UnlikelyBranchWeight > V) {
+      UnlikelyBranchWeight = V;
+    }
+  }
+
+  const uint64_t ProfiledWeight = RealWeights[MaxIndex];
+  const uint64_t RealWeightsTotal =
+      std::accumulate(RealWeights.begin(), RealWeights.end(), (uint64_t)0,
+                      std::plus<uint64_t>());
+  const uint64_t NumUnlikelyTargets = RealWeights.size() - 1;
+
+  const uint64_t TotalBranchWeight =
+      LikelyBranchWeight + (UnlikelyBranchWeight * NumUnlikelyTargets);
+
+  // To determine our threshold value we need to obtain the branch probability
+  // for the weights added by llvm.expect and use that proportion to calculate
+  // our threshold based on the collected profile data.
+  const llvm::BranchProbability LikelyProbablilty(LikelyBranchWeight,
+                                                  TotalBranchWeight);
+  uint64_t ScaledThreshold = LikelyProbablilty.scale(RealWeightsTotal);
+
+  // clamp tolerance range to [0, 100)
+  auto Tolerance = getMisExpectTolerance(I.getContext());
+  if (Tolerance < 0)
+    Tolerance = 0;
+  else if (MisExpectTolerance > 99)
+    Tolerance = 99;
+
+  // Allow users to relax checking by N%  i.e., if they use a 5% tolerance,
+  // then we check against 0.95*ScaledThreshold
+  if (Tolerance > 0)
+    ScaledThreshold *= (1.0 - Tolerance / 100.0);
+
+  // When the profile weight is below the threshold, we emit the diagnostic
+  if (ProfiledWeight < ScaledThreshold)
+    emitMisexpectDiagnostic(&I, I.getContext(), ProfiledWeight,
+                            RealWeightsTotal);
+}
+
+void checkBackendInstrumentation(Instruction &I,
+                                 const ArrayRef<uint32_t> RealWeights) {
+  auto ExpectedWeightsOpt = extractWeights(&I, I.getContext());
+  if (!ExpectedWeightsOpt.hasValue())
+    return;
+  auto ExpectedWeights = ExpectedWeightsOpt.getValue();
+  verifyMisExpect(I, RealWeights, ExpectedWeights);
+}
+
+void checkFrontendInstrumentation(Instruction &I,
+                                  const ArrayRef<uint32_t> ExpectedWeights) {
+  auto RealWeightsOpt = extractWeights(&I, I.getContext());
+  if (!RealWeightsOpt.hasValue())
+    return;
+  auto RealWeights = RealWeightsOpt.getValue();
+  verifyMisExpect(I, RealWeights, ExpectedWeights);
+}
+
+void checkExpectAnnotations(Instruction &I,
+                            const ArrayRef<uint32_t> ExistingWeights,
+                            bool IsFrontendInstr) {
+  if (IsFrontendInstr) {
+    checkFrontendInstrumentation(I, ExistingWeights);
+  } else {
+    checkBackendInstrumentation(I, ExistingWeights);
+  }
+}
+
+} // namespace misexpect
+} // namespace llvm
+#undef DEBUG_TYPE
Index: llvm/lib/Transforms/Utils/CMakeLists.txt
===================================================================
--- llvm/lib/Transforms/Utils/CMakeLists.txt
+++ llvm/lib/Transforms/Utils/CMakeLists.txt
@@ -53,6 +53,7 @@
   MemoryTaggingSupport.cpp
   Mem2Reg.cpp
   MetaRenamer.cpp
+  MisExpect.cpp
   ModuleUtils.cpp
   NameAnonGlobals.cpp
   PredicateInfo.cpp
Index: llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
+++ llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
@@ -25,6 +25,7 @@
 #include "llvm/Pass.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/MisExpect.h"
 
 using namespace llvm;
 
@@ -99,6 +100,8 @@
   uint64_t Index = (Case == *SI.case_default()) ? 0 : Case.getCaseIndex() + 1;
   Weights[Index] = LikelyBranchWeightVal;
 
+  misexpect::checkExpectAnnotations(SI, Weights, /*IsFrontend=*/true);
+
   SI.setCondition(ArgValue);
 
   SI.setMetadata(LLVMContext::MD_prof,
@@ -313,13 +316,16 @@
   std::tie(LikelyBranchWeightVal, UnlikelyBranchWeightVal) =
       getBranchWeight(Fn->getIntrinsicID(), CI, 2);
 
+  SmallVector<uint32_t, 4> ExpectedWeights;
   if ((ExpectedValue->getZExtValue() == ValueComparedTo) ==
       (Predicate == CmpInst::ICMP_EQ)) {
     Node =
         MDB.createBranchWeights(LikelyBranchWeightVal, UnlikelyBranchWeightVal);
+    ExpectedWeights = {LikelyBranchWeightVal, UnlikelyBranchWeightVal};
   } else {
     Node =
         MDB.createBranchWeights(UnlikelyBranchWeightVal, LikelyBranchWeightVal);
+    ExpectedWeights = {UnlikelyBranchWeightVal, LikelyBranchWeightVal};
   }
 
   if (CmpI)
@@ -327,6 +333,8 @@
   else
     BSI.setCondition(ArgValue);
 
+  misexpect::checkFrontendInstrumentation(BSI, ExpectedWeights);
+
   BSI.setMetadata(LLVMContext::MD_prof, Node);
 
   return true;
@@ -407,7 +415,7 @@
 
   bool runOnFunction(Function &F) override { return lowerExpectIntrinsic(F); }
 };
-}
+} // namespace
 
 char LowerExpectIntrinsic::ID = 0;
 INITIALIZE_PASS(LowerExpectIntrinsic, "lower-expect",
Index: llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -109,6 +109,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/MisExpect.h"
 #include "llvm/Transforms/Utils/ModuleUtils.h"
 #include <algorithm>
 #include <cassert>
@@ -2116,6 +2117,8 @@
     dbgs() << W << " ";
   } dbgs() << "\n";);
 
+  misexpect::checkExpectAnnotations(*TI, Weights, /*IsFrontend=*/false);
+
   TI->setMetadata(LLVMContext::MD_prof, MDB.createBranchWeights(Weights));
   if (EmitBranchProbability) {
     std::string BrCondStr = getBranchCondString(TI);
Index: llvm/lib/Transforms/IPO/SampleProfile.cpp
===================================================================
--- llvm/lib/Transforms/IPO/SampleProfile.cpp
+++ llvm/lib/Transforms/IPO/SampleProfile.cpp
@@ -84,6 +84,7 @@
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Utils/CallPromotionUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
+#include "llvm/Transforms/Utils/MisExpect.h"
 #include "llvm/Transforms/Utils/SampleProfileInference.h"
 #include "llvm/Transforms/Utils/SampleProfileLoaderBaseImpl.h"
 #include "llvm/Transforms/Utils/SampleProfileLoaderBaseUtil.h"
@@ -1733,6 +1734,8 @@
       }
     }
 
+    misexpect::checkExpectAnnotations(*TI, Weights, /*IsFrontend=*/false);
+
     uint64_t TempWeight;
     // Only set weights if there is at least one non-zero weight.
     // In any other case, let the analyzer set weights.
Index: llvm/lib/IR/LLVMContextImpl.h
===================================================================
--- llvm/lib/IR/LLVMContextImpl.h
+++ llvm/lib/IR/LLVMContextImpl.h
@@ -1380,6 +1380,11 @@
   /// If threshold option is not specified, it is disabled (0) by default.
   Optional<uint64_t> DiagnosticsHotnessThreshold = 0;
 
+  /// The percentage of difference between profiling branch weights and
+  // llvm.expect branch weights to tolerate when emiting MisExpect diagnostics
+  Optional<uint64_t> DiagnosticsMisExpectTolerance = 0;
+  bool MisExpectWarningRequested = false;
+
   /// The specialized remark streamer used by LLVM's OptimizationRemarkEmitter.
   std::unique_ptr<LLVMRemarkStreamer> LLVMRS;
 
Index: llvm/lib/IR/LLVMContext.cpp
===================================================================
--- llvm/lib/IR/LLVMContext.cpp
+++ llvm/lib/IR/LLVMContext.cpp
@@ -138,10 +138,22 @@
 void LLVMContext::setDiagnosticsHotnessThreshold(Optional<uint64_t> Threshold) {
   pImpl->DiagnosticsHotnessThreshold = Threshold;
 }
-
+void LLVMContext::setMisExpectWarningRequested(bool Requested) {
+  pImpl->MisExpectWarningRequested = Requested;
+}
+bool LLVMContext::getMisExpectWarningRequested() const {
+  return pImpl->MisExpectWarningRequested;
+}
 uint64_t LLVMContext::getDiagnosticsHotnessThreshold() const {
   return pImpl->DiagnosticsHotnessThreshold.getValueOr(UINT64_MAX);
 }
+void LLVMContext::setDiagnosticsMisExpectTolerance(
+    Optional<uint64_t> Tolerance) {
+  pImpl->DiagnosticsMisExpectTolerance = Tolerance;
+}
+uint64_t LLVMContext::getDiagnosticsMisExpectTolerance() const {
+  return pImpl->DiagnosticsMisExpectTolerance.getValueOr(0);
+}
 
 bool LLVMContext::isDiagnosticsHotnessThresholdSetFromPSI() const {
   return !pImpl->DiagnosticsHotnessThreshold.hasValue();
Index: llvm/lib/IR/DiagnosticInfo.cpp
===================================================================
--- llvm/lib/IR/DiagnosticInfo.cpp
+++ llvm/lib/IR/DiagnosticInfo.cpp
@@ -393,6 +393,17 @@
   return OS.str();
 }
 
+DiagnosticInfoMisExpect::DiagnosticInfoMisExpect(const Instruction *Inst,
+                                                 Twine &Msg)
+    : DiagnosticInfoWithLocationBase(DK_MisExpect, DS_Warning,
+                                     *Inst->getParent()->getParent(),
+                                     Inst->getDebugLoc()),
+      Msg(Msg) {}
+
+void DiagnosticInfoMisExpect::print(DiagnosticPrinter &DP) const {
+  DP << getLocationStr() << ": " << getMsg();
+}
+
 void OptimizationRemarkAnalysisFPCommute::anchor() {}
 void OptimizationRemarkAnalysisAliasing::anchor() {}
 
Index: llvm/include/llvm/Transforms/Utils/MisExpect.h
===================================================================
--- /dev/null
+++ llvm/include/llvm/Transforms/Utils/MisExpect.h
@@ -0,0 +1,77 @@
+//===--- MisExpect.h - Check the use of llvm.expect with PGO data ---------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This contains code to emit diagnostic messages for potentially incorrect
+// usage of the llvm.expect intrinsic. This utility extracts the threshold
+// values from metadata associated with the instrumented Branch or Switch
+// instruction. The threshold values are then used to determine if a diagnostic
+// should be emitted.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+
+namespace llvm {
+namespace misexpect {
+
+/// checkBackendInstrumentation - compares PGO counters to the thresholds used
+/// for llvm.expect and warns if the PGO counters are outside of the expected
+/// range. It extracts the expected weights from the MD_prof weights attatched
+/// to the instruction, which are are assumed to come from lowered llvm.expect
+/// intrinsics. The RealWeights parameter and the extracted expected weights are
+/// then passed to verifyMisexpect() for verification
+///
+/// \param I The Instruction being checked
+/// \param RealWeights A vector of profile weights for each target block
+void checkBackendInstrumentation(Instruction &I,
+                                 const llvm::ArrayRef<uint32_t> RealWeights);
+
+/// checkFrontendInstrumentation - compares PGO counters to the thresholds used
+/// for llvm.expect and warns if the PGO counters are outside of the expected
+/// range. It extracts the expected weights from the MD_prof weights attatched
+/// to the instruction, which are are assumed to come from profiling data
+/// attached by the frontend prior to llvm.expect intrinsic lowering. The
+/// ExpectedWeights parameter and the extracted real weights are then passed to
+/// verifyMisexpect() for verification
+///
+/// \param I The Instruction being checked
+/// \param ExpectedWeights A vector of the expected weights for each target
+/// block, this determines the threshold values used when emiting diagnostics
+void checkFrontendInstrumentation(Instruction &I,
+                                  const ArrayRef<uint32_t> ExpectedWeights);
+
+/// veryifyMisExpect - compares RealWeights to the thresholds used
+/// for llvm.expect and warns if the PGO counters are outside of the expected
+/// range.
+///
+/// \param I The Instruction being checked
+/// \param RealWeights A vector of profile weights from the profile data
+/// \param ExpectedWeights A vector of the weights attatch by llvm.expect
+void verifyMisExpect(Instruction &I, ArrayRef<uint32_t> RealWeights,
+                     const ArrayRef<uint32_t> ExpectedWeights);
+
+/// checkExpectAnnotations - compares PGO counters to the thresholds used
+/// for llvm.expect and warns if the PGO counters are outside of the expected
+/// range. It extracts the expected weights from the MD_prof weights attatched
+/// to the instruction, which are are assumed to come from lowered llvm.expect
+/// intrinsics. The RealWeights parameter and the extracted expected weights are
+/// then passed to verifyMisexpect() for verification. It is a thin wrapper
+/// around the checkFrontendInstrumentation and checkBackendInstrumentation APIs
+///
+/// \param I The Instruction being checked
+/// \param RealWeights A vector of profile weights for each target block
+/// \param IsBackend A boolean describing if this is Frontend instrumentation
+void checkExpectAnnotations(Instruction &I,
+                            const ArrayRef<uint32_t> ExistingWeights,
+                            bool IsFrontend);
+
+} // namespace misexpect
+} // namespace llvm
Index: llvm/include/llvm/Target/TargetOptions.h
===================================================================
--- llvm/include/llvm/Target/TargetOptions.h
+++ llvm/include/llvm/Target/TargetOptions.h
@@ -144,6 +144,7 @@
           ValueTrackingVariableLocations(false), ForceDwarfFrameSection(false),
           XRayOmitFunctionIndex(false), DebugStrictDwarf(false),
           Hotpatch(false), PPCGenScalarMASSEntries(false), JMCInstrument(false),
+          MisExpect(false),
           FPDenormalMode(DenormalMode::IEEE, DenormalMode::IEEE) {}
 
     /// DisableFramePointerElim - This returns true if frame pointer elimination
@@ -356,6 +357,10 @@
     /// Enable JustMyCode instrumentation.
     unsigned JMCInstrument : 1;
 
+    /// When set to true, enable MisExpect Diagnostics
+    /// By default, it is set to false
+    unsigned MisExpect : 1;
+
     /// Name of the stack usage file (i.e., .su file) if user passes
     /// -fstack-usage. If empty, it can be implied that -fstack-usage is not
     /// passed on the command line.
Index: llvm/include/llvm/IR/LLVMContext.h
===================================================================
--- llvm/include/llvm/IR/LLVMContext.h
+++ llvm/include/llvm/IR/LLVMContext.h
@@ -202,6 +202,11 @@
   /// diagnostics.
   void setDiagnosticsHotnessRequested(bool Requested);
 
+  bool getMisExpectWarningRequested() const;
+  void setMisExpectWarningRequested(bool Requested);
+  void setDiagnosticsMisExpectTolerance(Optional<uint64_t> Tolerance);
+  uint64_t getDiagnosticsMisExpectTolerance() const;
+
   /// Return the minimum hotness value a diagnostic would need in order
   /// to be included in optimization diagnostics.
   ///
Index: llvm/include/llvm/IR/DiagnosticInfo.h
===================================================================
--- llvm/include/llvm/IR/DiagnosticInfo.h
+++ llvm/include/llvm/IR/DiagnosticInfo.h
@@ -85,6 +85,7 @@
   DK_Unsupported,
   DK_SrcMgr,
   DK_DontCall,
+  DK_MisExpect,
   DK_FirstPluginKind // Must be last value to work with
                      // getNextAvailablePluginDiagnosticKind
 };
@@ -1032,6 +1033,25 @@
   void print(DiagnosticPrinter &DP) const override;
 };
 
+/// Diagnostic information for MisExpect analysis.
+class DiagnosticInfoMisExpect : public DiagnosticInfoWithLocationBase {
+public:
+  DiagnosticInfoMisExpect(const Instruction *Inst, Twine &Msg);
+
+  /// \see DiagnosticInfo::print.
+  void print(DiagnosticPrinter &DP) const override;
+
+  static bool classof(const DiagnosticInfo *DI) {
+    return DI->getKind() == DK_MisExpect;
+  }
+
+  const Twine &getMsg() const { return Msg; }
+
+private:
+  /// Message to report.
+  const Twine &Msg;
+};
+
 static DiagnosticSeverity getDiagnosticSeverity(SourceMgr::DiagKind DK) {
   switch (DK) {
   case llvm::SourceMgr::DK_Error:
Index: llvm/docs/MisExpect.rst
===================================================================
--- /dev/null
+++ llvm/docs/MisExpect.rst
@@ -0,0 +1,73 @@
+===================
+Misexpect
+===================
+.. contents::
+
+.. toctree::
+   :maxdepth: 1
+
+When developers use ``llvm.expect`` intrinsics, i.e., through use of
+``__builtin_expect(...)``, they are trying to communicate how their code is
+expected to behave at runtime to the optimizer. These annotations, however, can
+be incorrect for a variety of reasons: changes to the code base invalidate them
+silently, the developer mis-annotated them (e.g., using ``LIKELY`` instead of
+``UNLIKELY``), or perhaps they assumed something incorrectly when they wrote
+the annotation. Regardless of why, it is useful to detect these situations so
+that the optimizer can make more useful decisions about the code. MisExpect
+diagnostics are intended to help developers identify and address these
+situations, by comparing the use of the ``llvm.expect`` intrinsic to the ground
+truth provided by a profiling input.
+
+The MisExpect checks in the LLVM backend follow a simple procedure: if there is
+a mismatch between the branch weights collected during profiling and those
+supplied by an ``llvm.expect`` intrinsic, then it will emit a diagnostic
+message to the user.
+
+The most natural place to perform the verification is just prior to when
+branch weights are assigned to the target instruction in the form of
+branch weight metadata.
+
+There are 3 key places in the LLVM backend where branch weights are
+created and assigned based on profiling information or the use of the
+``llvm.expect`` intrinsic, and our implementation focuses on these
+places to perform the verification.
+
+We calculate the threshold for emitting MisExpect related diagnostics
+based on the values the compiler assigns to ``llvm.expect`` intrinsics,
+which can be set through the ``-likely-branch-weight`` and
+``-unlikely-branch-weight`` LLVM options. During verification, if the
+profile weights mismatch the calculated threshold, then we will emit a
+remark or warning detailing a potential performance regression. The
+diagnostic also reports the percentage of the time the annotation was
+correct during profiling to help developers reason about how to proceed.
+
+The diagnostics are also available in the form of optimization remarks,
+which can be serialized and processed through the ``opt-viewer.py``
+scripts in LLVM.
+
+.. option:: -pass-remarks=misexpect
+
+  Enables optimization remarks for misexpect when profiling data conflicts with
+  use of ``llvm.expect`` intrinsics.
+
+
+.. option:: -pgo-warn-misexpect
+
+  Enables misexpect warnings when profiling data conflicts with use of
+  ``llvm.expect`` intrinsics.
+
+LLVM supports 4 types of profile formats: Frontend, IR, CS-IR, and
+Sampling. MisExpect Diagnostics are compatible with all Profiling formats.
+
++----------------+--------------------------------------------------------------------------------------+
+| Profile Type   | Description                                                                          |
++================+======================================================================================+
+| Frontend       | Profiling instrumentation added during compilation by the frontend, i.e. ``clang``    |
++----------------+--------------------------------------------------------------------------------------+
+| IR             | Profiling instrumentation added during by the LLVM backend                           |
++----------------+--------------------------------------------------------------------------------------+
+| CS-IR          | Context Sensitive IR based profiles                                                  |
++----------------+--------------------------------------------------------------------------------------+
+| Sampling       | Profiles collected through sampling with external tools, such as ``perf`` on Linux   |
++----------------+--------------------------------------------------------------------------------------+
+
Index: clang/test/Profile/misexpect-switch.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-switch.c
@@ -0,0 +1,39 @@
+// Test that misexpect detects mis-annotated switch statements
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-switch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect -debug-info-kind=line-tables-only
+
+#define inner_loop 1000
+#define outer_loop 20
+#define arry_size 25
+
+int arry[arry_size] = {0};
+
+int rand();
+int sum(int *buff, int size);
+int random_sample(int *buff, int size);
+
+int main() {
+  int val = 0;
+
+  int j, k;
+  for (j = 0; j < outer_loop; ++j) {
+    for (k = 0; k < inner_loop; ++k) {
+      unsigned condition = rand() % 10000;
+      switch (__builtin_expect(condition, 0)) { // expected-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% ({{[0-9]+ / [0-9]+}}) of profiled executions.}}
+      case 0:
+        val += sum(arry, arry_size);
+        break;
+      case 1:
+      case 2:
+      case 3:
+        break;
+      default:
+        val += random_sample(arry, arry_size);
+        break;
+      } // end switch
+    }   // end inner_loop
+  }     // end outer_loop
+
+  return 0;
+}
Index: clang/test/Profile/misexpect-switch-only-default-case.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-switch-only-default-case.c
@@ -0,0 +1,36 @@
+// Test that misexpect emits no warning when there is only one switch case
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-switch-default-only.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect -debug-info-kind=line-tables-only
+
+// expected-no-diagnostics
+
+#define inner_loop 1000
+#define outer_loop 20
+#define arry_size 25
+
+int sum(int *buff, int size);
+int random_sample(int *buff, int size);
+int rand();
+void init_arry();
+
+int arry[arry_size] = {0};
+
+int main() {
+  init_arry();
+  int val = 0;
+
+  int j, k;
+  for (j = 0; j < outer_loop; ++j) {
+    for (k = 0; k < inner_loop; ++k) {
+      unsigned condition = rand() % 10000;
+      switch (__builtin_expect(condition, 0)) {
+      default:
+        val += random_sample(arry, arry_size);
+        break;
+      }; // end switch
+    }    // end inner_loop
+  }      // end outer_loop
+
+  return 0;
+}
Index: clang/test/Profile/misexpect-switch-nonconst.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-switch-nonconst.c
@@ -0,0 +1,44 @@
+// Test that misexpect emits no warning when switch condition is non-const
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-switch-nonconst.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify
+
+// expected-no-diagnostics
+
+#define inner_loop 1000
+#define outer_loop 20
+#define arry_size 25
+
+int sum(int *buff, int size);
+int random_sample(int *buff, int size);
+int rand();
+void init_arry();
+
+int arry[arry_size] = {0};
+
+int main() {
+  init_arry();
+  int val = 0;
+
+  int j, k;
+  for (j = 0; j < outer_loop; ++j) {
+    for (k = 0; k < inner_loop; ++k) {
+      unsigned condition = rand() % 10000;
+      switch (__builtin_expect(condition, rand())) {
+      case 0:
+        val += sum(arry, arry_size);
+        break;
+      case 1:
+      case 2:
+      case 3:
+      case 4:
+        val += random_sample(arry, arry_size);
+        break;
+      default:
+        __builtin_unreachable();
+      } // end switch
+    }   // end inner_loop
+  }     // end outer_loop
+
+  return 0;
+}
Index: clang/test/Profile/misexpect-switch-default.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-switch-default.c
@@ -0,0 +1,40 @@
+// Test that misexpect detects mis-annotated switch statements for default case
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-switch-default.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect -debug-info-kind=line-tables-only
+
+#define inner_loop 1000
+#define outer_loop 20
+#define arry_size 25
+
+int sum(int *buff, int size);
+int random_sample(int *buff, int size);
+int rand();
+void init_arry();
+
+int arry[arry_size] = {0};
+
+int main() {
+  init_arry();
+  int val = 0;
+  int j;
+  for (j = 0; j < outer_loop * inner_loop; ++j) {
+    unsigned condition = rand() % 5;
+    switch (__builtin_expect(condition, 6)) { // expected-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% ({{[0-9]+ / [0-9]+}}) of profiled executions.}}
+    case 0:
+      val += sum(arry, arry_size);
+      break;
+    case 1:
+    case 2:
+    case 3:
+      break;
+    case 4:
+      val += random_sample(arry, arry_size);
+      break;
+    default:
+      __builtin_unreachable();
+    } // end switch
+  }   // end outer_loop
+
+  return 0;
+}
Index: clang/test/Profile/misexpect-branch.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-branch.c
@@ -0,0 +1,49 @@
+// Test that misexpect detects mis-annotated branches
+
+// test diagnostics are issued when profiling data mis-matches annotations
+// RUN: llvm-profdata merge %S/Inputs/misexpect-branch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify=imprecise -Wmisexpect
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify=exact -Wmisexpect -debug-info-kind=line-tables-only
+
+// there should be no diagnostics when the tolerance is sufficiently high, or when -Wmisexpect is not requested
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify=foo -fdiagnostics-misexpect-tolerance=10 -Wmisexpect -debug-info-kind=line-tables-only
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify=foo
+
+// Ensure we emit an error when we don't use pgo with tolerance threshold
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm  -fdiagnostics-misexpect-tolerance=10 -Wmisexpect -debug-info-kind=line-tables-only 2>&1 | FileCheck -check-prefix=NO_PGO %s
+
+// Test -fdiagnostics-misexpect-tolerance=  requires pgo profile
+// NO_PGO: '-fdiagnostics-misexpect-tolerance=' requires profile-guided optimization information
+
+// foo-no-diagnostics
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+int foo(int);
+int baz(int);
+int buzz();
+
+const int inner_loop = 100;
+const int outer_loop = 2000;
+
+int bar() { // imprecise-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% ({{[0-9]+ / [0-9]+}}) of profiled executions.}}
+  int rando = buzz();
+  int x = 0;
+  if (likely(rando % (outer_loop * inner_loop) == 0)) { // exact-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% ({{[0-9]+ / [0-9]+}}) of profiled executions.}}
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
+
+int fizz() { // imprecise-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% ({{[0-9]+ / [0-9]+}}) of profiled executions.}}
+  int rando = buzz();
+  int x = 0;
+  if (unlikely(rando % (outer_loop * inner_loop) == 0)) { // exact-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% ({{[0-9]+ / [0-9]+}}) of profiled executions.}}
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
Index: clang/test/Profile/misexpect-branch-unpredictable.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-branch-unpredictable.c
@@ -0,0 +1,25 @@
+// Test that misexpect emits no warning when prediction is correct
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-branch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+// expected-no-diagnostics
+#define unpredictable(x) __builtin_unpredictable(!!(x))
+
+int foo(int);
+int baz(int);
+int buzz();
+
+const int inner_loop = 100;
+const int outer_loop = 2000;
+
+int bar() {
+  int rando = buzz();
+  int x = 0;
+  if (unpredictable(rando % (outer_loop * inner_loop) == 0)) {
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
Index: clang/test/Profile/misexpect-branch-nonconst-expected-val.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-branch-nonconst-expected-val.c
@@ -0,0 +1,23 @@
+// Test that misexpect emits no warning when condition is not a compile-time constant
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-branch-nonconst-expect-arg.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+// expected-no-diagnostics
+int foo(int);
+int baz(int);
+int buzz();
+
+const int inner_loop = 100;
+const int outer_loop = 2000;
+
+int bar() {
+  int rando = buzz();
+  int x = 0;
+  if (__builtin_expect(rando % (outer_loop * inner_loop) == 0, buzz())) {
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
Index: clang/test/Profile/misexpect-branch-cold.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-branch-cold.c
@@ -0,0 +1,26 @@
+// Test that misexpect emits no warning when prediction is correct
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-branch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+// expected-no-diagnostics
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+int foo(int);
+int baz(int);
+int buzz();
+
+const int inner_loop = 100;
+const int outer_loop = 2000;
+
+int bar() {
+  int rando = buzz();
+  int x = 0;
+  if (unlikely(rando % (outer_loop * inner_loop) == 0)) {
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
Index: clang/test/Profile/Inputs/misexpect-switch.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-switch.proftext
@@ -0,0 +1,32 @@
+main
+# Func Hash:
+872687477373597607
+# Num Counters:
+9
+# Counter Values:
+1
+20
+20000
+20000
+3
+3
+1
+3
+19990
+
+random_sample
+# Func Hash:
+24
+# Num Counters:
+1
+# Counter Values:
+19990
+
+sum
+# Func Hash:
+24
+# Num Counters:
+1
+# Counter Values:
+3
+
Index: clang/test/Profile/Inputs/misexpect-switch-nonconst.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-switch-nonconst.proftext
@@ -0,0 +1,16 @@
+main
+# Func Hash:
+3721743393642630379
+# Num Counters:
+10
+# Counter Values:
+1
+20
+20000
+20000
+1
+0
+0
+0
+19999
+0
Index: clang/test/Profile/Inputs/misexpect-switch-default.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-switch-default.proftext
@@ -0,0 +1,16 @@
+main
+# Func Hash:
+8734802134600123338
+# Num Counters:
+9
+# Counter Values:
+1
+20000
+20000
+4066
+11889
+0
+0
+4045
+0
+
Index: clang/test/Profile/Inputs/misexpect-switch-default-only.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-switch-default-only.proftext
@@ -0,0 +1,12 @@
+main
+# Func Hash:
+79676873694057560
+# Num Counters:
+5
+# Counter Values:
+1
+20
+20000
+20000
+20000
+
Index: clang/test/Profile/Inputs/misexpect-branch.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-branch.proftext
@@ -0,0 +1,17 @@
+bar
+# Func Hash:
+45795613684824
+# Num Counters:
+2
+# Counter Values:
+200000
+180000
+
+fizz
+# Func Hash:
+45795613684824
+# Num Counters:
+2
+# Counter Values:
+200000
+18000
Index: clang/test/Profile/Inputs/misexpect-branch-nonconst-expect-arg.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-branch-nonconst-expect-arg.proftext
@@ -0,0 +1,8 @@
+bar
+# Func Hash:
+11262309464
+# Num Counters:
+2
+# Counter Values:
+200000
+2
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -106,6 +106,20 @@
 using namespace options;
 using namespace llvm::opt;
 
+//===----------------------------------------------------------------------===//
+// Helpers.
+//===----------------------------------------------------------------------===//
+
+// Parse misexpect tolerance argument value.
+// Valid option values are integers in the range [0, 100)
+inline Expected<Optional<uint64_t>> parseToleranceOption(StringRef Arg) {
+  int64_t Val;
+  if (Arg.getAsInteger(10, Val))
+    return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                   "Not an integer: %s", Arg.data());
+  return Val;
+}
+
 //===----------------------------------------------------------------------===//
 // Initialization.
 //===----------------------------------------------------------------------===//
@@ -1535,6 +1549,9 @@
                   : "auto",
               SA);
 
+  GenerateArg(Args, OPT_fdiagnostics_misexpect_tolerance_EQ,
+              Twine(*Opts.DiagnosticsMisExpectTolerance), SA);
+
   for (StringRef Sanitizer : serializeSanitizerKinds(Opts.SanitizeRecover))
     GenerateArg(Args, OPT_fsanitize_recover_EQ, Sanitizer, SA);
 
@@ -1952,6 +1969,21 @@
     }
   }
 
+  if (auto *arg =
+          Args.getLastArg(options::OPT_fdiagnostics_misexpect_tolerance_EQ)) {
+    auto ResultOrErr = parseToleranceOption(arg->getValue());
+
+    if (!ResultOrErr) {
+      Diags.Report(diag::err_drv_invalid_diagnotics_misexpect_tolerance)
+          << "-fdiagnostics-misexpect-tolerance=";
+    } else {
+      Opts.DiagnosticsMisExpectTolerance = *ResultOrErr;
+      if (!UsingProfile)
+        Diags.Report(diag::warn_drv_diagnostics_misexpect_requires_pgo)
+            << "-fdiagnostics-misexpect-tolerance=";
+    }
+  }
+
   // If the user requested to use a sample profile for PGO, then the
   // backend will need to track source location information so the profile
   // can be incorporated into the IR.
@@ -4497,6 +4529,13 @@
   if (Res.getFrontendOpts().ProgramAction == frontend::RewriteObjC)
     LangOpts.ObjCExceptions = 1;
 
+  for (auto Warning : Res.getDiagnosticOpts().Warnings) {
+    if (Warning == "misexpect" &&
+        !Diags.isIgnored(diag::warn_profile_data_misexpect, SourceLocation())) {
+      Res.getCodeGenOpts().MisExpect = true;
+    }
+  }
+
   if (LangOpts.CUDA) {
     // During CUDA device-side compilation, the aux triple is the
     // triple used for host compilation.
Index: clang/lib/CodeGen/CodeGenAction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenAction.cpp
+++ clang/lib/CodeGen/CodeGenAction.cpp
@@ -340,6 +340,15 @@
           CodeGenOpts.getProfileUse() != CodeGenOptions::ProfileNone)
         Ctx.setDiagnosticsHotnessRequested(true);
 
+      if (CodeGenOpts.MisExpect) {
+        Ctx.setMisExpectWarningRequested(true);
+      }
+
+      if (CodeGenOpts.DiagnosticsMisExpectTolerance) {
+        Ctx.setDiagnosticsMisExpectTolerance(
+            CodeGenOpts.DiagnosticsMisExpectTolerance);
+      }
+
       // Link each LinkModule into our module.
       if (LinkInModules())
         return;
@@ -440,6 +449,9 @@
     void OptimizationFailureHandler(
         const llvm::DiagnosticInfoOptimizationFailure &D);
     void DontCallDiagHandler(const DiagnosticInfoDontCall &D);
+    /// Specialized handler for misexpect warnings.
+    /// Note that misexpect remarks are emitted through ORE
+    void MisExpectDiagHandler(const llvm::DiagnosticInfoMisExpect &D);
   };
 
   void BackendConsumer::anchor() {}
@@ -821,6 +833,25 @@
       << llvm::demangle(D.getFunctionName().str()) << D.getNote();
 }
 
+void BackendConsumer::MisExpectDiagHandler(
+    const llvm::DiagnosticInfoMisExpect &D) {
+  StringRef Filename;
+  unsigned Line, Column;
+  bool BadDebugInfo = false;
+  FullSourceLoc Loc =
+      getBestLocationFromDebugLoc(D, BadDebugInfo, Filename, Line, Column);
+
+  Diags.Report(Loc, diag::warn_profile_data_misexpect) << D.getMsg().str();
+
+  if (BadDebugInfo)
+    // If we were not able to translate the file:line:col information
+    // back to a SourceLocation, at least emit a note stating that
+    // we could not translate this location. This can happen in the
+    // case of #line directives.
+    Diags.Report(Loc, diag::note_fe_backend_invalid_loc)
+        << Filename << Line << Column;
+}
+
 /// This function is invoked when the backend needs
 /// to report something to the user.
 void BackendConsumer::DiagnosticHandlerImpl(const DiagnosticInfo &DI) {
@@ -895,6 +926,9 @@
   case llvm::DK_DontCall:
     DontCallDiagHandler(cast<DiagnosticInfoDontCall>(DI));
     return;
+  case llvm::DK_MisExpect:
+    MisExpectDiagHandler(cast<DiagnosticInfoMisExpect>(DI));
+    return;
   default:
     // Plugin IDs are not bound to any value as they are set dynamically.
     ComputeDiagRemarkID(Severity, backend_plugin, DiagID);
Index: clang/lib/CodeGen/BackendUtil.cpp
===================================================================
--- clang/lib/CodeGen/BackendUtil.cpp
+++ clang/lib/CodeGen/BackendUtil.cpp
@@ -650,6 +650,7 @@
           Entry.IgnoreSysRoot ? Entry.Path : HSOpts.Sysroot + Entry.Path);
   Options.MCOptions.Argv0 = CodeGenOpts.Argv0;
   Options.MCOptions.CommandLineArgs = CodeGenOpts.CommandLineArgs;
+  Options.MisExpect = CodeGenOpts.MisExpect;
 
   return true;
 }
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -1424,6 +1424,9 @@
     Group<f_Group>, Flags<[CC1Option]>, MetaVarName<"<value>">,
     HelpText<"Prevent optimization remarks from being output if they do not have at least this profile count. "
     "Use 'auto' to apply the threshold from profile summary">;
+def fdiagnostics_misexpect_tolerance_EQ : Joined<["-"], "fdiagnostics-misexpect-tolerance=">,
+    Group<f_Group>, Flags<[CC1Option]>, MetaVarName<"<value>">,
+    HelpText<"Prevent misexpect diagnostics from being output if the profile counts are within N% of the expected. ">;
 defm diagnostics_show_option : BoolFOption<"diagnostics-show-option",
     DiagnosticOpts<"ShowOptionNames">, DefaultTrue,
     NegFlag<SetFalse, [CC1Option]>, PosFlag<SetTrue, [], "Print option name with mappable diagnostics">>;
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -1249,6 +1249,7 @@
 def ProfileInstrMissing : DiagGroup<"profile-instr-missing">;
 def ProfileInstrOutOfDate : DiagGroup<"profile-instr-out-of-date">;
 def ProfileInstrUnprofiled : DiagGroup<"profile-instr-unprofiled">;
+def MisExpect : DiagGroup<"misexpect">;
 
 // AddressSanitizer frontend instrumentation remarks.
 def SanitizeAddressRemarks : DiagGroup<"sanitize-address">;
Index: clang/include/clang/Basic/DiagnosticFrontendKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticFrontendKinds.td
+++ clang/include/clang/Basic/DiagnosticFrontendKinds.td
@@ -311,6 +311,11 @@
 def warn_profile_data_unprofiled : Warning<
   "no profile data available for file \"%0\"">,
   InGroup<ProfileInstrUnprofiled>;
+def warn_profile_data_misexpect : Warning<
+  "Potential performance regression from use of __builtin_expect(): "
+  "Annotation was correct on %0 of profiled executions.">,
+  BackendInfo,
+  InGroup<MisExpect>;
 } // end of instrumentation issue category
 
 }
Index: clang/include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -149,6 +149,8 @@
   "invalid Darwin version number: %0">;
 def err_drv_invalid_diagnotics_hotness_threshold : Error<
   "invalid argument in '%0', only integer or 'auto' is supported">;
+def err_drv_invalid_diagnotics_misexpect_tolerance : Error<
+  "invalid argument in '%0', only integers are supported">;
 def err_drv_missing_argument : Error<
   "argument to '%0' is missing (expected %1 value%s1)">;
 def err_drv_invalid_Xarch_argument_with_args : Error<
@@ -374,6 +376,9 @@
 def warn_drv_diagnostics_hotness_requires_pgo : Warning<
   "argument '%0' requires profile-guided optimization information">,
   InGroup<UnusedCommandLineArgument>;
+def warn_drv_diagnostics_misexpect_requires_pgo : Warning<
+  "argument '%0' requires profile-guided optimization information">,
+  InGroup<UnusedCommandLineArgument>;
 def warn_drv_clang_unsupported : Warning<
   "the clang compiler does not support '%0'">;
 def warn_drv_deprecated_arg : Warning<
Index: clang/include/clang/Basic/CodeGenOptions.h
===================================================================
--- clang/include/clang/Basic/CodeGenOptions.h
+++ clang/include/clang/Basic/CodeGenOptions.h
@@ -420,6 +420,10 @@
   /// If threshold option is not specified, it is disabled by default.
   Optional<uint64_t> DiagnosticsHotnessThreshold = 0;
 
+  /// The maximum percentage profiling weights can deviate from the expected
+  /// values in order to be included in misexpect diagnostics.
+  Optional<uint64_t> DiagnosticsMisExpectTolerance = 0;
+
 public:
   // Define accessors/mutators for code generation options of enumeration type.
 #define CODEGENOPT(Name, Bits, Default)
Index: clang/include/clang/Basic/CodeGenOptions.def
===================================================================
--- clang/include/clang/Basic/CodeGenOptions.def
+++ clang/include/clang/Basic/CodeGenOptions.def
@@ -175,6 +175,7 @@
 CODEGENOPT(FatalWarnings     , 1, 0) ///< Set when -Wa,--fatal-warnings is
                                      ///< enabled.
 CODEGENOPT(NoWarn            , 1, 0) ///< Set when -Wa,--no-warn is enabled.
+CODEGENOPT(MisExpect         , 1, 0) ///< Set when -Wmisexpect is enabled
 CODEGENOPT(EnableSegmentedStacks , 1, 0) ///< Set when -fsplit-stack is enabled.
 CODEGENOPT(NoInlineLineTables, 1, 0) ///< Whether debug info should contain
                                      ///< inline line tables.
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -68,6 +68,9 @@
   constants that are not representable in a casted value. For example,
   ``(float) f == 0.1`` is always false.
 
+- ``-Wmisexpect`` warns when the branch weights collected during profiling
+  conflict with those added by ``llvm.expect``.
+
 Non-comprehensive list of changes in this release
 -------------------------------------------------
 
Index: clang/docs/MisExpect.rst
===================================================================
--- /dev/null
+++ clang/docs/MisExpect.rst
@@ -0,0 +1,75 @@
+===================
+Misexpect
+===================
+.. contents::
+
+.. toctree::
+   :maxdepth: 1
+
+When developers use ``llvm.expect`` intrinsics, i.e., through use of
+``__builtin_expect(...)``, they are trying to communicate how their code is
+expected to behave at runtime to the optimizer. These annotations, however, can
+be incorrect for a variety of reasons: changes to the code base invalidate them
+silently, the developer mis-annotated them (e.g., using ``LIKELY`` instead of
+``UNLIKELY``), or perhaps they assumed something incorrectly when they wrote
+the annotation. Regardless of why, it is useful to detect these situations so
+that the optimizer can make more useful decisions about the code. 
+
+MisExpect diagnostics are intended to help developers identify and address
+these situations, by comparing the branch weights added by the ``llvm.expect``
+intrinsic to those collected through profiling. Whenever these values are
+mismatched, a diagnostic is surfaced to the user. Details on how the checks
+operate in the LLVM backed can be found in LLVM's documentation.
+
+By default MisExpect checking is quite strict, because the use of the
+``llvm.expect`` intrinsic is designed for specialized cases, where the outcome
+of a condition is severely skewed. As a result, the optimizer can be extremely
+aggressive, which can result in performance degradation if the outcome is less
+predictable than the annotation suggests. Even when the annotation is correct
+90% of the time, it may be beneficial to either remove the annotation or to use
+a different intrinsic that can communicate the probability more directly.
+
+Because this may be too strict, MisExpect diagnostics are not enabled by
+default, and support an additional flag to tolerate some deviation from the
+exact thresholds. The ``-fdiagnostic-misexpect-tolerance=N`` accepts
+deviations when comparing branch weights within ``N%`` of the expected values.
+So passing ``-fdiagnostic-misexpect-tolerance=5`` will not report diagnostic messages
+if the branch weight from the profile is within 5% of the weight added by
+the ``llvm.expect`` intrinsic.
+
+MisExpect diagnostics are also available in the form of optimization remarks,
+which can be serialized and processed through the ``opt-viewer.py``
+scripts in LLVM.
+
+.. option:: -Rpass=misexpect
+
+  Enables optimization remarks for misexpect when profiling data conflicts with
+  use of ``llvm.expect`` intrinsics.
+
+
+.. option:: -Wmisexpect
+
+  Enables misexpect warnings when profiling data conflicts with use of
+  ``llvm.expect`` intrinsics.
+
+.. option:: -fdiagnostic-misexpect-tolerance=N
+
+   Relaxes misexpect checking to tolerate profiling values within N% of the 
+   expected branch weight. e.g., a value of ``N=5`` allows misexpect to check against
+   ``0.95 * Threshold``
+
+LLVM supports 4 types of profile formats: Frontend, IR, CS-IR, and
+Sampling. MisExpect Diagnostics are compatible with all Profiling formats.
+
++----------------+--------------------------------------------------------------------------------------+
+| Profile Type   | Description                                                                          |
++================+======================================================================================+
+| Frontend       | Profiling instrumentation added during compilation by the frontend, i.e. ``clang``    |
++----------------+--------------------------------------------------------------------------------------+
+| IR             | Profiling instrumentation added during by the LLVM backend                           |
++----------------+--------------------------------------------------------------------------------------+
+| CS-IR          | Context Sensitive IR based profiles                                                  |
++----------------+--------------------------------------------------------------------------------------+
+| Sampling       | Profiles collected through sampling with external tools, such as ``perf`` on Linux   |
++----------------+--------------------------------------------------------------------------------------+
+

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