https://github.com/Lancern created
https://github.com/llvm/llvm-project/pull/144726
This patch adds support for the `__builtin_expect` and
`__builtin_expect_with_probability` builtin functions.
>From 684994022716f10c83aadeaa8985d6842064bb9e Mon Sep 17 00:00:00 2001
From: Sirui Mu <msrlanc...@gmail.com>
Date: Wed, 18 Jun 2025 23:25:10 +0800
Subject: [PATCH] [CIR] Add support for __builtin_expect
This patch adds support for the __builtin_expect and
__builtin_expect_with_probability builtin functions.
---
clang/include/clang/CIR/Dialect/IR/CIROps.td | 37 +++++++++++
clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp | 33 ++++++++++
.../CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp | 14 +++++
.../CIR/Lowering/DirectToLLVM/LowerToLLVM.h | 10 +++
clang/test/CIR/CodeGen/builtin-o1.cpp | 62 +++++++++++++++++++
clang/test/CIR/CodeGen/builtin_call.cpp | 16 +++++
6 files changed, 172 insertions(+)
create mode 100644 clang/test/CIR/CodeGen/builtin-o1.cpp
diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td
b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index 4655cebc82ee7..f98929d96c79c 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -2409,4 +2409,41 @@ def AssumeOp : CIR_Op<"assume"> {
}];
}
+//===----------------------------------------------------------------------===//
+// Branch Probability Operations
+//===----------------------------------------------------------------------===//
+
+def ExpectOp : CIR_Op<"expect",
+ [Pure, AllTypesMatch<["result", "val", "expected"]>]> {
+ let summary = "Tell the optimizer that two values are likely to be equal.";
+ let description = [{
+ The `cir.expect` operation may take 2 or 3 arguments.
+
+ When the argument `prob` is missing, this operation effectively models the
+ `__builtin_expect` builtin function. It tells the optimizer that `val` and
+ `expected` are likely to be equal.
+
+ When the argumen `prob` is present, this operation effectively models the
+ `__builtin_expect_with_probability` builtin function. It tells the
+ optimizer that `val` and `expected` are equal to each other with a certain
+ probability.
+
+ `val` and `expected` must be integers and their types must match.
+
+ The result of this operation is always equal to `val`.
+ }];
+
+ let arguments = (ins
+ CIR_AnyFundamentalIntType:$val,
+ CIR_AnyFundamentalIntType:$expected,
+ OptionalAttr<F64Attr>:$prob
+ );
+
+ let results = (outs CIR_AnyFundamentalIntType:$result);
+
+ let assemblyFormat = [{
+ `(` $val`,` $expected (`,` $prob^)? `)` `:` type($val) attr-dict
+ }];
+}
+
#endif // CLANG_CIR_DIALECT_IR_CIROPS_TD
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index 83825f0835a1e..33f10ea05d2a3 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -91,6 +91,39 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd,
unsigned builtinID,
builder.create<cir::AssumeOp>(getLoc(e->getExprLoc()), argValue);
return RValue::get(nullptr);
}
+
+ case Builtin::BI__builtin_expect:
+ case Builtin::BI__builtin_expect_with_probability: {
+ mlir::Value argValue = emitScalarExpr(e->getArg(0));
+ mlir::Value expectedValue = emitScalarExpr(e->getArg(1));
+
+ // Don't generate cir.expect on -O0 as the backend won't use it for
+ // anything. Note, we still generate expectedValue because it could have
+ // side effects.
+ if (cgm.getCodeGenOpts().OptimizationLevel == 0)
+ return RValue::get(argValue);
+
+ mlir::FloatAttr probAttr;
+ if (builtinIDIfNoAsmLabel == Builtin::BI__builtin_expect_with_probability)
{
+ llvm::APFloat probability(0.0);
+ const Expr *probArg = e->getArg(2);
+ bool evalSucceeded =
+ probArg->EvaluateAsFloat(probability, cgm.getASTContext());
+ assert(evalSucceeded &&
+ "probability should be able to evaluate as float");
+ (void)evalSucceeded;
+ bool loseInfo = false;
+ probability.convert(llvm::APFloat::IEEEdouble(),
+ llvm::RoundingMode::Dynamic, &loseInfo);
+ probAttr =
mlir::FloatAttr::get(mlir::Float64Type::get(&getMLIRContext()),
+ probability);
+ }
+
+ auto result = builder.create<cir::ExpectOp>(getLoc(e->getSourceRange()),
+ argValue.getType(), argValue,
+ expectedValue, probAttr);
+ return RValue::get(result);
+ }
}
cgm.errorNYI(e->getSourceRange(), "unimplemented builtin call");
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
index a96501ab2c384..9ca726e315baf 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -948,6 +948,19 @@ mlir::LogicalResult
CIRToLLVMConstantOpLowering::matchAndRewrite(
return mlir::success();
}
+mlir::LogicalResult CIRToLLVMExpectOpLowering::matchAndRewrite(
+ cir::ExpectOp op, OpAdaptor adaptor,
+ mlir::ConversionPatternRewriter &rewriter) const {
+ std::optional<llvm::APFloat> prob = op.getProb();
+ if (prob)
+ rewriter.replaceOpWithNewOp<mlir::LLVM::ExpectWithProbabilityOp>(
+ op, adaptor.getVal(), adaptor.getExpected(), prob.value());
+ else
+ rewriter.replaceOpWithNewOp<mlir::LLVM::ExpectOp>(op, adaptor.getVal(),
+ adaptor.getExpected());
+ return mlir::success();
+}
+
/// Convert the `cir.func` attributes to `llvm.func` attributes.
/// Only retain those attributes that are not constructed by
/// `LLVMFuncOp::build`. If `filterArgAttrs` is set, also filter out
@@ -1827,6 +1840,7 @@ void ConvertCIRToLLVMPass::runOnOperation() {
CIRToLLVMCallOpLowering,
CIRToLLVMCmpOpLowering,
CIRToLLVMConstantOpLowering,
+ CIRToLLVMExpectOpLowering,
CIRToLLVMFuncOpLowering,
CIRToLLVMGetGlobalOpLowering,
CIRToLLVMGetMemberOpLowering,
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
index a80c66ac1abf2..ef614cea9ae01 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
@@ -65,6 +65,16 @@ class CIRToLLVMCastOpLowering : public
mlir::OpConversionPattern<cir::CastOp> {
mlir::ConversionPatternRewriter &) const override;
};
+class CIRToLLVMExpectOpLowering
+ : public mlir::OpConversionPattern<cir::ExpectOp> {
+public:
+ using mlir::OpConversionPattern<cir::ExpectOp>::OpConversionPattern;
+
+ mlir::LogicalResult
+ matchAndRewrite(cir::ExpectOp op, OpAdaptor,
+ mlir::ConversionPatternRewriter &) const override;
+};
+
class CIRToLLVMReturnOpLowering
: public mlir::OpConversionPattern<cir::ReturnOp> {
public:
diff --git a/clang/test/CIR/CodeGen/builtin-o1.cpp
b/clang/test/CIR/CodeGen/builtin-o1.cpp
new file mode 100644
index 0000000000000..94e6b7a5ce550
--- /dev/null
+++ b/clang/test/CIR/CodeGen/builtin-o1.cpp
@@ -0,0 +1,62 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux-gnu -O1
-Wno-unused-value -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s -check-prefix=CIR
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux-gnu -O1
-disable-llvm-passes -Wno-unused-value -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s -check-prefix=LLVM
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux-gnu -O1
-disable-llvm-passes -Wno-unused-value -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
+
+void expect(int x, int y) {
+ __builtin_expect(x, y);
+}
+
+// CIR-LABEL: cir.func @_Z6expectii
+// CIR: %[[X:.+]] = cir.load align(4) %{{.+}} : !cir.ptr<!s32i>, !s32i
+// CIR-NEXT: %[[X_LONG:.+]] = cir.cast(integral, %[[X]] : !s32i), !s64i
+// CIR-NEXT: %[[Y:.+]] = cir.load align(4) %{{.+}} : !cir.ptr<!s32i>, !s32i
+// CIR-NEXT: %[[Y_LONG:.+]] = cir.cast(integral, %[[Y]] : !s32i), !s64i
+// CIR-NEXT: %{{.+}} = cir.expect(%[[X_LONG]], %[[Y_LONG]]) : !s64i
+// CIR: }
+
+// LLVM-LABEL: define void @_Z6expectii
+// LLVM: %[[X:.+]] = load i32, ptr %{{.+}}, align 4
+// LLVM-NEXT: %[[X_LONG:.+]] = sext i32 %[[X]] to i64
+// LLVM-NEXT: %[[Y:.+]] = load i32, ptr %{{.+}}, align 4
+// LLVM-NEXT: %[[Y_LONG:.+]] = sext i32 %[[Y]] to i64
+// LLVM-NEXT: %{{.+}} = call i64 @llvm.expect.i64(i64 %[[X_LONG]], i64
%[[Y_LONG]])
+// LLVM: }
+
+// OGCG-LABEL: define {{.*}}void @_Z6expectii
+// OGCG: %[[X:.+]] = load i32, ptr %{{.+}}, align 4
+// OGCG-NEXT: %[[X_LONG:.+]] = sext i32 %[[X]] to i64
+// OGCG-NEXT: %[[Y:.+]] = load i32, ptr %{{.+}}, align 4
+// OGCG-NEXT: %[[Y_LONG:.+]] = sext i32 %[[Y]] to i64
+// OGCG-NEXT: %{{.+}} = call i64 @llvm.expect.i64(i64 %[[X_LONG]], i64
%[[Y_LONG]])
+// OGCG: }
+
+void expect_prob(int x, int y) {
+ __builtin_expect_with_probability(x, y, 0.25);
+}
+
+// CIR-LABEL: cir.func @_Z11expect_probii
+// CIR: %[[X:.+]] = cir.load align(4) %{{.+}} : !cir.ptr<!s32i>, !s32i
+// CIR-NEXT: %[[X_LONG:.+]] = cir.cast(integral, %[[X]] : !s32i), !s64i
+// CIR-NEXT: %[[Y:.+]] = cir.load align(4) %{{.+}} : !cir.ptr<!s32i>, !s32i
+// CIR-NEXT: %[[Y_LONG:.+]] = cir.cast(integral, %[[Y]] : !s32i), !s64i
+// CIR-NEXT: %{{.+}} = cir.expect(%[[X_LONG]], %[[Y_LONG]], 2.500000e-01) :
!s64i
+// CIR: }
+
+// LLVM: define void @_Z11expect_probii
+// LLVM: %[[X:.+]] = load i32, ptr %{{.+}}, align 4
+// LLVM-NEXT: %[[X_LONG:.+]] = sext i32 %[[X]] to i64
+// LLVM-NEXT: %[[Y:.+]] = load i32, ptr %{{.+}}, align 4
+// LLVM-NEXT: %[[Y_LONG:.+]] = sext i32 %[[Y]] to i64
+// LLVM-NEXT: %{{.+}} = call i64 @llvm.expect.with.probability.i64(i64
%[[X_LONG]], i64 %[[Y_LONG]], double 2.500000e-01)
+// LLVM: }
+
+// OGCG-LABEL: define {{.*}}void @_Z11expect_probii
+// OGCG: %[[X:.+]] = load i32, ptr %{{.+}}, align 4
+// OGCG-NEXT: %[[X_LONG:.+]] = sext i32 %[[X]] to i64
+// OGCG-NEXT: %[[Y:.+]] = load i32, ptr %{{.+}}, align 4
+// OGCG-NEXT: %[[Y_LONG:.+]] = sext i32 %[[Y]] to i64
+// OGCG-NEXT: %{{.+}} = call i64 @llvm.expect.with.probability.i64(i64
%[[X_LONG]], i64 %[[Y_LONG]], double 2.500000e-01)
+// OGCG: }
diff --git a/clang/test/CIR/CodeGen/builtin_call.cpp
b/clang/test/CIR/CodeGen/builtin_call.cpp
index 0a2226a2cc592..996a3bd7828b5 100644
--- a/clang/test/CIR/CodeGen/builtin_call.cpp
+++ b/clang/test/CIR/CodeGen/builtin_call.cpp
@@ -110,3 +110,19 @@ void assume(bool arg) {
// OGCG: define {{.*}}void @_Z6assumeb
// OGCG: call void @llvm.assume(i1 %{{.+}})
// OGCG: }
+
+void expect(int x, int y) {
+ __builtin_expect(x, y);
+}
+
+// CIR: cir.func @_Z6expectii
+// CIR-NOT: cir.expect
+// CIR: }
+
+void expect_prob(int x, int y) {
+ __builtin_expect_with_probability(x, y, 0.25);
+}
+
+// CIR: cir.func @_Z11expect_probii
+// CIR-NOT: cir.expect
+// CIR: }
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