vsk created this revision.
vsk added reviewers: djtodoro, aprantl, dstenb.
Herald added subscribers: lldb-commits, hiraditya.
Herald added projects: LLDB, LLVM.
A struct argument can be passed-by-value to a callee via a pointer to a
temporary stack copy. Add support for emitting an entry value DBG_VALUE
when an indirect parameter DBG_VALUE becomes unavailable. This is done
by omitting DW_OP_stack_value from the entry value expression, to make
the expression describe the location of an object.
rdar://63373691
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D80345
Files:
lldb/test/API/functionalities/param_entry_vals/basic_entry_values/main.cpp
llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
llvm/lib/CodeGen/LiveDebugValues.cpp
llvm/test/DebugInfo/MIR/AArch64/dbgcall-site-indirect-param.mir
Index: llvm/test/DebugInfo/MIR/AArch64/dbgcall-site-indirect-param.mir
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/MIR/AArch64/dbgcall-site-indirect-param.mir
@@ -0,0 +1,143 @@
+# RUN: llc -emit-call-site-info -start-before=livedebugvalues -filetype=obj -o - %s \
+# RUN: | llvm-dwarfdump - | FileCheck %s -implicit-check-not=DW_OP_entry_value
+
+# // Original Source
+# struct fat_ptr {
+# int *ptr, *low, *high;
+# };
+# extern int baz(int x);
+# int bar(struct fat_ptr f) {
+# return baz(baz(*f.ptr));
+# }
+
+# After w0 is clobbered, we should get an indirect parameter entry value for "f".
+
+# CHECK-LABEL: DW_TAG_formal_parameter
+# CHECK-NEXT: DW_AT_location
+# CHECK-NEXT: [0x0000000000000000, 0x0000000000000010): DW_OP_breg0 W0+0
+# CHECK-NEXT: [0x0000000000000010, 0x000000000000001c): DW_OP_entry_value(DW_OP_reg0 W0))
+# CHECK-NEXT: DW_AT_name ("f")
+
+--- |
+ target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+ target triple = "arm64-apple-ios10.0.0"
+
+ %struct.fat_ptr = type { i32*, i32*, i32* }
+
+ define i32 @bar(%struct.fat_ptr* nocapture readonly %f) local_unnamed_addr !dbg !13 {
+ entry:
+ call void @llvm.dbg.declare(metadata %struct.fat_ptr* %f, metadata !23, metadata !DIExpression()), !dbg !24
+ %ptr2 = bitcast %struct.fat_ptr* %f to i32**, !dbg !25
+ %0 = load i32*, i32** %ptr2, align 8, !dbg !25
+ %1 = load i32, i32* %0, align 4, !dbg !31
+ %call = tail call i32 @baz(i32 %1), !dbg !34
+ %call1 = tail call i32 @baz(i32 %call), !dbg !35
+ ret i32 %call1, !dbg !36
+ }
+
+ declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+ declare !dbg !4 i32 @baz(i32) local_unnamed_addr optsize
+
+ !llvm.dbg.cu = !{!0}
+ !llvm.module.flags = !{!8, !9, !10, !11}
+ !llvm.ident = !{!12}
+
+ !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None, sysroot: "/")
+ !1 = !DIFile(filename: "indirect.c", directory: "/tmp/fatptr")
+ !2 = !{}
+ !3 = !{!4}
+ !4 = !DISubprogram(name: "baz", scope: !1, file: !1, line: 4, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+ !5 = !DISubroutineType(types: !6)
+ !6 = !{!7, !7}
+ !7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+ !8 = !{i32 7, !"Dwarf Version", i32 4}
+ !9 = !{i32 2, !"Debug Info Version", i32 3}
+ !10 = !{i32 1, !"wchar_size", i32 4}
+ !11 = !{i32 7, !"PIC Level", i32 2}
+ !12 = !{!"clang"}
+ !13 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 5, type: !14, scopeLine: 5, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !22)
+ !14 = !DISubroutineType(types: !15)
+ !15 = !{!7, !16}
+ !16 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "fat_ptr", file: !1, line: 1, size: 192, elements: !17)
+ !17 = !{!18, !20, !21}
+ !18 = !DIDerivedType(tag: DW_TAG_member, name: "ptr", scope: !16, file: !1, line: 2, baseType: !19, size: 64)
+ !19 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !7, size: 64)
+ !20 = !DIDerivedType(tag: DW_TAG_member, name: "low", scope: !16, file: !1, line: 2, baseType: !19, size: 64, offset: 64)
+ !21 = !DIDerivedType(tag: DW_TAG_member, name: "high", scope: !16, file: !1, line: 2, baseType: !19, size: 64, offset: 128)
+ !22 = !{!23}
+ !23 = !DILocalVariable(name: "f", arg: 1, scope: !13, file: !1, line: 5, type: !16)
+ !24 = !DILocation(line: 5, column: 24, scope: !13)
+ !25 = !DILocation(line: 6, column: 23, scope: !13)
+ !31 = !DILocation(line: 6, column: 20, scope: !13)
+ !34 = !DILocation(line: 6, column: 16, scope: !13)
+ !35 = !DILocation(line: 6, column: 12, scope: !13)
+ !36 = !DILocation(line: 6, column: 5, scope: !13)
+
+...
+---
+name: bar
+alignment: 4
+exposesReturnsTwice: false
+legalized: false
+regBankSelected: false
+selected: false
+failedISel: false
+tracksRegLiveness: true
+hasWinCFI: false
+registers: []
+liveins:
+ - { reg: '$x0', virtual-reg: '' }
+frameInfo:
+ isFrameAddressTaken: false
+ isReturnAddressTaken: false
+ hasStackMap: false
+ hasPatchPoint: false
+ stackSize: 16
+ offsetAdjustment: 0
+ maxAlignment: 8
+ adjustsStack: true
+ hasCalls: true
+ stackProtector: ''
+ maxCallFrameSize: 0
+ cvBytesOfCalleeSavedRegisters: 0
+ hasOpaqueSPAdjustment: false
+ hasVAStart: false
+ hasMustTailInVarArgFunc: false
+ localFrameSize: 0
+ savePoint: ''
+ restorePoint: ''
+fixedStack: []
+stack:
+ - { id: 0, name: '', type: spill-slot, offset: -8, size: 8, alignment: 8,
+ stack-id: default, callee-saved-register: '$lr', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+ - { id: 1, name: '', type: spill-slot, offset: -16, size: 8, alignment: 8,
+ stack-id: default, callee-saved-register: '$fp', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:
+ - { bb: 0, offset: 9, fwdArgRegs:
+ - { arg: 0, reg: '$w0' } }
+ - { bb: 0, offset: 11, fwdArgRegs:
+ - { arg: 0, reg: '$w0' } }
+constants: []
+machineFunctionInfo:
+ hasRedZone: false
+body: |
+ bb.0.entry:
+ liveins: $x0, $lr
+
+ DBG_VALUE $x0, 0, !23, !DIExpression(), debug-location !24
+ DBG_VALUE $x0, 0, !23, !DIExpression(), debug-location !24
+ early-clobber $sp = frame-setup STPXpre killed $fp, killed $lr, $sp, -2 :: (store 8 into %stack.1), (store 8 into %stack.0)
+ $fp = frame-setup ADDXri $sp, 0, 0
+ frame-setup CFI_INSTRUCTION def_cfa $w29, 16
+ frame-setup CFI_INSTRUCTION offset $w30, -8, debug-location !25
+ frame-setup CFI_INSTRUCTION offset $w29, -16, debug-location !25
+ renamable $x8 = LDRXui killed renamable $x0, 0, debug-location !25 :: (load 8 from %ir.ptr2)
+ renamable $w0 = LDRWui killed renamable $x8, 0, debug-location !31 :: (load 4 from %ir.0)
+ BL @baz, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit $w0, implicit-def $sp, implicit-def $w0, debug-location !34
+ early-clobber $sp, $fp, $lr = frame-destroy LDPXpost $sp, 2, debug-location !35 :: (load 8 from %stack.1), (load 8 from %stack.0)
+ TCRETURNdi @baz, 0, csr_aarch64_aapcs, implicit $sp, implicit $w0, debug-location !35
+
+...
Index: llvm/lib/CodeGen/LiveDebugValues.cpp
===================================================================
--- llvm/lib/CodeGen/LiveDebugValues.cpp
+++ llvm/lib/CodeGen/LiveDebugValues.cpp
@@ -1612,10 +1612,6 @@
if (MI.getDebugLoc()->getInlinedAt())
return false;
- // Do not consider indirect debug values (TODO: explain why).
- if (MI.isIndirectDebugValue())
- return false;
-
// Only consider parameters that are described using registers. Parameters
// that are passed on the stack are not yet supported, so ignore debug
// values that are described by the frame or stack pointer.
@@ -1630,7 +1626,7 @@
return false;
// TODO: Add support for parameters that have a pre-existing debug expressions
- // (e.g. fragments, or indirect parameters using DW_OP_deref).
+ // (e.g. fragments).
if (MI.getDebugExpression()->getNumElements() > 0)
return false;
Index: llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
+++ llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
@@ -19,6 +19,7 @@
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/MC/MachineLocation.h"
#include <cassert>
#include <cstdint>
#include <iterator>
@@ -143,10 +144,14 @@
enum { Unknown = 0, Register, Memory, Implicit };
/// The flags of location description being produced.
- enum { EntryValue = 1, CallSiteParamValue };
+ enum {
+ EntryValue = 1 << 0,
+ IndirectEntryValue = 1 << 1,
+ CallSiteParamValue = 1 << 2
+ };
unsigned LocationKind : 3;
- unsigned LocationFlags : 2;
+ unsigned LocationFlags : 3;
unsigned DwarfVersion : 4;
public:
@@ -160,6 +165,10 @@
bool isEntryValue() const { return LocationFlags & EntryValue; }
+ bool isIndirectEntryValue() const {
+ return LocationFlags & IndirectEntryValue;
+ }
+
bool isParameterValue() { return LocationFlags & CallSiteParamValue; }
Optional<uint8_t> TagOffset;
@@ -296,7 +305,9 @@
}
/// Lock this down to become an entry value location.
- void setEntryValueFlag() { LocationFlags |= EntryValue; }
+ void setEntryValueFlagFromLoc(MachineLocation Loc) {
+ LocationFlags |= Loc.isIndirect() ? IndirectEntryValue : EntryValue;
+ }
/// Lock this down to become a call site parameter location.
void setCallSiteParamValueFlag() { LocationFlags |= CallSiteParamValue; }
Index: llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -249,14 +249,14 @@
// location, emit it with addBReg and offset 0, because we should emit a DWARF
// expression representing a value, rather than a location.
if (!isMemoryLocation() && !HasComplexExpression &&
- (!isParameterValue() || isEntryValue())) {
+ (!isParameterValue() || isEntryValue() || isIndirectEntryValue())) {
for (auto &Reg : DwarfRegs) {
if (Reg.DwarfRegNo >= 0)
addReg(Reg.DwarfRegNo, Reg.Comment);
addOpPiece(Reg.SubRegSize);
}
- if (isEntryValue())
+ if (isEntryValue() || isIndirectEntryValue())
finalizeEntryValue();
if (isEntryValue() && !isParameterValue() && DwarfVersion >= 4)
Index: llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -786,6 +786,8 @@
// Emit the call site parameter's value as an entry value.
if (ShouldTryEmitEntryVals) {
// Create an expression where the register's entry value is used.
+ // FIXME: This produces unusable descriptions when the register contains
+ // a pointer to a temporary copy of a struct passed by value.
DIExpression *EntryExpr = DIExpression::get(
MF->getFunction().getContext(), {dwarf::DW_OP_LLVM_entry_value, 1});
for (auto RegEntry : ForwardedRegWorklist) {
@@ -2399,12 +2401,12 @@
DwarfExpr.addUnsignedConstant(Value.getInt());
} else if (Value.isLocation()) {
MachineLocation Location = Value.getLoc();
- if (Location.isIndirect())
+ if (Location.isIndirect() && !DIExpr->isEntryValue())
DwarfExpr.setMemoryLocationKind();
DIExpressionCursor Cursor(DIExpr);
if (DIExpr->isEntryValue()) {
- DwarfExpr.setEntryValueFlag();
+ DwarfExpr.setEntryValueFlagFromLoc(Location);
DwarfExpr.beginEntryValueExpression(Cursor);
}
Index: llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -1285,13 +1285,13 @@
DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
const DIExpression *DIExpr = DV.getSingleExpression();
DwarfExpr.addFragmentOffset(DIExpr);
- if (Location.isIndirect())
+ if (Location.isIndirect() && !DIExpr->isEntryValue())
DwarfExpr.setMemoryLocationKind();
DIExpressionCursor Cursor(DIExpr);
if (DIExpr->isEntryValue()) {
- DwarfExpr.setEntryValueFlag();
+ DwarfExpr.setEntryValueFlagFromLoc(Location);
DwarfExpr.beginEntryValueExpression(Cursor);
}
Index: lldb/test/API/functionalities/param_entry_vals/basic_entry_values/main.cpp
===================================================================
--- lldb/test/API/functionalities/param_entry_vals/basic_entry_values/main.cpp
+++ lldb/test/API/functionalities/param_entry_vals/basic_entry_values/main.cpp
@@ -137,6 +137,30 @@
target_no_tailcall(sink, 123);
}
+/// A structure that is guaranteed -- when passed to a callee by value -- to be
+/// passed via a pointer to a temporary copy in the caller. On x86_64 & aarch64
+/// only.
+struct StructPassedViaPointerToTemporaryCopy {
+ // Under the 64-bit AAPCS, a struct larger than 16 bytes is not SROA'd, and
+ // is instead passed via pointer to a temporary copy.
+ long a, b, c;
+ StructPassedViaPointerToTemporaryCopy() : a(1), b(2), c(3) {}
+
+ // Failing that, a virtual method forces passing via pointer to a temporary
+ // copy under the common calling conventions (e.g. 32/64-bit x86, Linux/Win,
+ // according to https://www.agner.org/optimize/calling_conventions.pdf).
+ virtual void add_vtable() {}
+};
+
+__attribute__((noinline)) void func15(StructPassedViaPointerToTemporaryCopy S) {
+ use<StructPassedViaPointerToTemporaryCopy &>(S);
+ use<int &>(dummy);
+
+ ++global;
+ //% self.filecheck("expr S", "main.cpp", "-check-prefix=FUNC15-EXPR")
+ // FUNC15-EXPR: (a = 1, b = 2, c = 3)
+}
+
__attribute__((disable_tail_calls)) int main() {
int sink = 0;
S1 s1;
@@ -169,5 +193,9 @@
// Test that evaluation can "see through" an indirect tail call.
func14(sink, func13);
+ // Test evaluation of an entry value that dereferences a temporary stack
+ // slot set up by the caller for a StructPassedViaPointerToTemporaryCopy.
+ func15(StructPassedViaPointerToTemporaryCopy());
+
return 0;
}
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