forked from OSchip/llvm-project
[DebugInfo] Emit DW_OP_implicit_value for Floating point constants
llvm is missing support for DW_OP_implicit_value operation.
DW_OP_implicit_value op is indispensable for cases such as
optimized out long double variables.
For intro refer: DWARFv5 Spec Pg: 40 2.6.1.1.4 Implicit Location Descriptions
Consider the following example:
```
int main() {
long double ld = 3.14;
printf("dummy\n");
ld *= ld;
return 0;
}
```
when compiled with tunk `clang` as
`clang test.c -g -O1` produces following location description
of variable `ld`:
```
DW_AT_location (0x00000000:
[0x0000000000201691, 0x000000000020169b): DW_OP_constu 0xc8f5c28f5c28f800, DW_OP_stack_value, DW_OP_piece 0x8, DW_OP_constu 0x4000, DW_OP_stack_value, DW_OP_bit_piece 0x10 0x40, DW_OP_stack_value)
DW_AT_name ("ld")
```
Here one may notice that this representation is incorrect(DWARF4
stack could only hold integers(and only up to the size of address)).
Here the variable size itself is `128` bit.
GDB and LLDB confirms this:
```
(gdb) p ld
$1 = <invalid float value>
(lldb) frame variable ld
(long double) ld = <extracting data from value failed>
```
GCC represents/uses DW_OP_implicit_value in these sort of situations.
Based on the discussion with Jakub Jelinek regarding GCC's motivation
for using this, I concluded that DW_OP_implicit_value is most appropriate
in this case.
Link: https://gcc.gnu.org/pipermail/gcc/2020-July/233057.html
GDB seems happy after this patch:(LLDB doesn't have support
for DW_OP_implicit_value)
```
(gdb) p ld
p ld
$1 = 3.14000000000000012434
```
Reviewed By: aprantl
Differential Revision: https://reviews.llvm.org/D83560
This commit is contained in:
Sourabh Singh Tomar
parent
9f5210aacf
commit
15801f1619
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@ -2501,8 +2501,21 @@ void DwarfDebug::emitDebugLocValue(const AsmPrinter &AP, const DIBasicType *BT,
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DwarfExpr.addExpression(std::move(ExprCursor));
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return;
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} else if (Value.isConstantFP()) {
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APInt RawBytes = Value.getConstantFP()->getValueAPF().bitcastToAPInt();
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DwarfExpr.addUnsignedConstant(RawBytes);
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if (AP.getDwarfVersion() >= 4 && AP.getDwarfDebug()->tuneForGDB()) {
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DwarfExpr.addConstantFP(Value.getConstantFP()->getValueAPF(), AP);
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return;
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} else if (Value.getConstantFP()
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->getValueAPF()
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.bitcastToAPInt()
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.getBitWidth() <= 64 /*bits*/)
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DwarfExpr.addUnsignedConstant(
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Value.getConstantFP()->getValueAPF().bitcastToAPInt());
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else
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LLVM_DEBUG(
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dbgs()
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<< "Skipped DwarfExpression creation for ConstantFP of size"
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<< Value.getConstantFP()->getValueAPF().bitcastToAPInt().getBitWidth()
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<< " bits\n");
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}
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DwarfExpr.addExpression(std::move(ExprCursor));
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}
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@ -17,6 +17,7 @@
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#include "llvm/BinaryFormat/Dwarf.h"
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#include "llvm/CodeGen/Register.h"
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#include "llvm/CodeGen/TargetRegisterInfo.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DebugInfoMetadata.h"
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#include "llvm/Support/ErrorHandling.h"
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#include <algorithm>
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@ -25,6 +26,8 @@
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using namespace llvm;
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#define DEBUG_TYPE "dwarfdebug"
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void DwarfExpression::emitConstu(uint64_t Value) {
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if (Value < 32)
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emitOp(dwarf::DW_OP_lit0 + Value);
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@ -219,6 +222,31 @@ void DwarfExpression::addUnsignedConstant(const APInt &Value) {
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}
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}
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void DwarfExpression::addConstantFP(const APFloat &APF, const AsmPrinter &AP) {
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assert(isImplicitLocation() || isUnknownLocation());
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APInt API = APF.bitcastToAPInt();
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int NumBytes = API.getBitWidth() / 8;
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if (NumBytes == 4 /*float*/ || NumBytes == 8 /*double*/) {
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// FIXME: Add support for `long double`.
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emitOp(dwarf::DW_OP_implicit_value);
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emitUnsigned(NumBytes /*Size of the block in bytes*/);
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const uint64_t *Value = API.getRawData();
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const bool IsLittleEndian = AP.getDataLayout().isLittleEndian();
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uint64_t Swapped = support::endian::byte_swap(
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*Value, IsLittleEndian ? support::little : support::big);
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const char *SwappedBytes = reinterpret_cast<const char *>(&Swapped);
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for (int i = 0; i < NumBytes; ++i)
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emitData1(SwappedBytes[i]);
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return;
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}
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LLVM_DEBUG(
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dbgs() << "Skipped DW_OP_implicit_value creation for ConstantFP of size: "
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<< API.getBitWidth() << " bits\n");
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}
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bool DwarfExpression::addMachineRegExpression(const TargetRegisterInfo &TRI,
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DIExpressionCursor &ExprCursor,
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unsigned MachineReg,
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@ -299,6 +299,9 @@ public:
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/// Emit an unsigned constant.
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void addUnsignedConstant(const APInt &Value);
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/// Emit an floating point constant.
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void addConstantFP(const APFloat &Value, const AsmPrinter &AP);
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/// Lock this down to become a memory location description.
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void setMemoryLocationKind() {
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assert(isUnknownLocation());
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@ -20,12 +20,10 @@
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;
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; CHECK: .debug_info contents:
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; CHECK: DW_TAG_variable
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; CHECK-NEXT: DW_AT_location {{.*}} (
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; CHECK-NEXT: [0x[[START:.*]], 0x[[END:.*]]): DW_OP_constu 0xc8f5c28f5c28f800, DW_OP_piece 0x8, DW_OP_constu 0x4000, DW_OP_bit_piece 0x10 0x40)
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; CHECK-NEXT: DW_AT_name {{.*}}"ld"
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; CHECK: DW_TAG_variable
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; CHECK-NEXT: DW_AT_location {{.*}} (
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; CHECK-NEXT: [0x[[START]], 0x[[END]]): DW_OP_constu 0x4048f5c3)
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; CHECK-NEXT: [0x{{.*}}, 0x{{.*}}): DW_OP_constu 0x4048f5c3)
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; CHECK-NEXT: DW_AT_name {{.*}}"f"
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source_filename = "test.c"
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@ -0,0 +1,66 @@
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;; This test checks for emission of DW_OP_implicit_value operation
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;; for double type.
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; RUN: llc -debugger-tune=gdb -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
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; CHECK: .debug_info contents:
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; CHECK: DW_TAG_variable
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; CHECK-NEXT: DW_AT_location ({{.*}}
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; CHECK-NEXT: [{{.*}}): DW_OP_implicit_value 0x8 0x1f 0x85 0xeb 0x51 0xb8 0x1e 0x09 0x40)
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; CHECK-NEXT: DW_AT_name ("d")
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;; Generated from: clang -ggdb -O1
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;;int main() {
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;; double d = 3.14;
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;; printf("dummy\n");
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;; d *= d;
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;; return 0;
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;;}
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; ModuleID = 'implicit_value-double.c'
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source_filename = "implicit_value-double.c"
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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@str = private unnamed_addr constant [6 x i8] c"dummy\00", align 1
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; Function Attrs: nofree nounwind uwtable
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define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 {
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entry:
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call void @llvm.dbg.value(metadata double 3.140000e+00, metadata !12, metadata !DIExpression()), !dbg !14
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%puts = call i32 @puts(i8* nonnull dereferenceable(1) getelementptr inbounds ([6 x i8], [6 x i8]* @str, i64 0, i64 0)), !dbg !15
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call void @llvm.dbg.value(metadata double undef, metadata !12, metadata !DIExpression()), !dbg !14
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ret i32 0, !dbg !16
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}
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; Function Attrs: nounwind readnone speculatable willreturn
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declare void @llvm.dbg.value(metadata, metadata, metadata) #1
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; Function Attrs: nofree nounwind
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declare i32 @puts(i8* nocapture readonly) local_unnamed_addr #2
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attributes #0 = { nofree nounwind uwtable }
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attributes #1 = { nounwind readnone speculatable willreturn }
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attributes #2 = { nofree nounwind }
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!3, !4, !5}
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!llvm.ident = !{!6}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
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!1 = !DIFile(filename: "implicit_value-double.c", directory: "/home/")
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!2 = !{}
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!3 = !{i32 7, !"Dwarf Version", i32 4}
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!4 = !{i32 2, !"Debug Info Version", i32 3}
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!5 = !{i32 1, !"wchar_size", i32 4}
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!6 = !{!"clang version 11.0.0"}
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!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
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!8 = !DISubroutineType(types: !9)
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!9 = !{!10}
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!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!11 = !{!12}
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!12 = !DILocalVariable(name: "d", scope: !7, file: !1, line: 2, type: !13)
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!13 = !DIBasicType(name: "double", size: 64, encoding: DW_ATE_float)
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!14 = !DILocation(line: 0, scope: !7)
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!15 = !DILocation(line: 3, column: 2, scope: !7)
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!16 = !DILocation(line: 5, column: 2, scope: !7)
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@ -0,0 +1,65 @@
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;; This test checks for emission of DW_OP_implicit_value operation
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;; for float type.
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; RUN: llc -debugger-tune=gdb -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
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; CHECK: .debug_info contents:
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; CHECK: DW_TAG_variable
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; CHECK-NEXT: DW_AT_location ({{.*}}
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; CHECK-NEXT: [{{.*}}): DW_OP_implicit_value 0x4 0xc3 0xf5 0x48 0x40)
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; CHECK-NEXT: DW_AT_name ("f")
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;; Generated from: clang -ggdb -O1
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;;int main() {
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;; float f = 3.14f;
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;; printf("dummy\n");
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;; f *= f;
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;; return 0;
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;;}
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; ModuleID = 'implicit_value-float.c'
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source_filename = "implicit_value-float.c"
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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@str = private unnamed_addr constant [6 x i8] c"dummy\00", align 1
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; Function Attrs: nofree nounwind uwtable
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define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 {
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entry:
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call void @llvm.dbg.value(metadata float 0x40091EB860000000, metadata !12, metadata !DIExpression()), !dbg !14
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%puts = call i32 @puts(i8* nonnull dereferenceable(1) getelementptr inbounds ([6 x i8], [6 x i8]* @str, i64 0, i64 0)), !dbg !15
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call void @llvm.dbg.value(metadata float undef, metadata !12, metadata !DIExpression()), !dbg !14
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ret i32 0, !dbg !16
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}
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; Function Attrs: nounwind readnone speculatable willreturn
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declare void @llvm.dbg.value(metadata, metadata, metadata) #1
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; Function Attrs: nofree nounwind
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declare i32 @puts(i8* nocapture readonly) local_unnamed_addr #2
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attributes #0 = { nofree nounwind uwtable }
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attributes #1 = { nounwind readnone speculatable willreturn }
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attributes #2 = { nofree nounwind }
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!3, !4, !5}
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!llvm.ident = !{!6}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
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!1 = !DIFile(filename: "implicit_value-float.c", directory: "/home/")
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!2 = !{}
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!3 = !{i32 7, !"Dwarf Version", i32 4}
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!4 = !{i32 2, !"Debug Info Version", i32 3}
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!5 = !{i32 1, !"wchar_size", i32 4}
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!6 = !{!"clang version 11.0.0"}
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!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
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!8 = !DISubroutineType(types: !9)
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!9 = !{!10}
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!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!11 = !{!12}
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!12 = !DILocalVariable(name: "f", scope: !7, file: !1, line: 2, type: !13)
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!13 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
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!14 = !DILocation(line: 0, scope: !7)
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!15 = !DILocation(line: 3, column: 2, scope: !7)
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!16 = !DILocation(line: 5, column: 2, scope: !7)
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