[llvm] 15801f1 - [DebugInfo] Emit DW_OP_implicit_value for Floating point constants
Sourabh Singh Tomar via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 19 12:51:21 PDT 2020
Author: Sourabh Singh Tomar
Date: 2020-08-20T01:20:40+05:30
New Revision: 15801f16194a3da6bc9ae5b869815178993303e7
URL: https://github.com/llvm/llvm-project/commit/15801f16194a3da6bc9ae5b869815178993303e7
DIFF: https://github.com/llvm/llvm-project/commit/15801f16194a3da6bc9ae5b869815178993303e7.diff
LOG: [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
Added:
llvm/test/DebugInfo/X86/implicit_value-double.ll
llvm/test/DebugInfo/X86/implicit_value-float.ll
Modified:
llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
llvm/test/DebugInfo/X86/float_const_loclist.ll
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index cee72120accb..0730fff3bcaf 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2501,8 +2501,21 @@ void DwarfDebug::emitDebugLocValue(const AsmPrinter &AP, const DIBasicType *BT,
DwarfExpr.addExpression(std::move(ExprCursor));
return;
} else if (Value.isConstantFP()) {
- APInt RawBytes = Value.getConstantFP()->getValueAPF().bitcastToAPInt();
- DwarfExpr.addUnsignedConstant(RawBytes);
+ if (AP.getDwarfVersion() >= 4 && AP.getDwarfDebug()->tuneForGDB()) {
+ DwarfExpr.addConstantFP(Value.getConstantFP()->getValueAPF(), AP);
+ return;
+ } else if (Value.getConstantFP()
+ ->getValueAPF()
+ .bitcastToAPInt()
+ .getBitWidth() <= 64 /*bits*/)
+ DwarfExpr.addUnsignedConstant(
+ Value.getConstantFP()->getValueAPF().bitcastToAPInt());
+ else
+ LLVM_DEBUG(
+ dbgs()
+ << "Skipped DwarfExpression creation for ConstantFP of size"
+ << Value.getConstantFP()->getValueAPF().bitcastToAPInt().getBitWidth()
+ << " bits\n");
}
DwarfExpr.addExpression(std::move(ExprCursor));
}
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index d4762121d105..4455035d8910 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -17,6 +17,7 @@
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
+#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
@@ -25,6 +26,8 @@
using namespace llvm;
+#define DEBUG_TYPE "dwarfdebug"
+
void DwarfExpression::emitConstu(uint64_t Value) {
if (Value < 32)
emitOp(dwarf::DW_OP_lit0 + Value);
@@ -219,6 +222,31 @@ void DwarfExpression::addUnsignedConstant(const APInt &Value) {
}
}
+void DwarfExpression::addConstantFP(const APFloat &APF, const AsmPrinter &AP) {
+ assert(isImplicitLocation() || isUnknownLocation());
+ APInt API = APF.bitcastToAPInt();
+ int NumBytes = API.getBitWidth() / 8;
+ if (NumBytes == 4 /*float*/ || NumBytes == 8 /*double*/) {
+ // FIXME: Add support for `long double`.
+ emitOp(dwarf::DW_OP_implicit_value);
+ emitUnsigned(NumBytes /*Size of the block in bytes*/);
+
+ const uint64_t *Value = API.getRawData();
+ const bool IsLittleEndian = AP.getDataLayout().isLittleEndian();
+ uint64_t Swapped = support::endian::byte_swap(
+ *Value, IsLittleEndian ? support::little : support::big);
+
+ const char *SwappedBytes = reinterpret_cast<const char *>(&Swapped);
+ for (int i = 0; i < NumBytes; ++i)
+ emitData1(SwappedBytes[i]);
+
+ return;
+ }
+ LLVM_DEBUG(
+ dbgs() << "Skipped DW_OP_implicit_value creation for ConstantFP of size: "
+ << API.getBitWidth() << " bits\n");
+}
+
bool DwarfExpression::addMachineRegExpression(const TargetRegisterInfo &TRI,
DIExpressionCursor &ExprCursor,
unsigned MachineReg,
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
index 757b17511453..78a98a61178f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
@@ -299,6 +299,9 @@ class DwarfExpression {
/// Emit an unsigned constant.
void addUnsignedConstant(const APInt &Value);
+ /// Emit an floating point constant.
+ void addConstantFP(const APFloat &Value, const AsmPrinter &AP);
+
/// Lock this down to become a memory location description.
void setMemoryLocationKind() {
assert(isUnknownLocation());
diff --git a/llvm/test/DebugInfo/X86/float_const_loclist.ll b/llvm/test/DebugInfo/X86/float_const_loclist.ll
index f9008209e5df..24ee16444836 100644
--- a/llvm/test/DebugInfo/X86/float_const_loclist.ll
+++ b/llvm/test/DebugInfo/X86/float_const_loclist.ll
@@ -20,12 +20,10 @@
;
; CHECK: .debug_info contents:
; CHECK: DW_TAG_variable
-; CHECK-NEXT: DW_AT_location {{.*}} (
-; CHECK-NEXT: [0x[[START:.*]], 0x[[END:.*]]): DW_OP_constu 0xc8f5c28f5c28f800, DW_OP_piece 0x8, DW_OP_constu 0x4000, DW_OP_bit_piece 0x10 0x40)
; CHECK-NEXT: DW_AT_name {{.*}}"ld"
; CHECK: DW_TAG_variable
; CHECK-NEXT: DW_AT_location {{.*}} (
-; CHECK-NEXT: [0x[[START]], 0x[[END]]): DW_OP_constu 0x4048f5c3)
+; CHECK-NEXT: [0x{{.*}}, 0x{{.*}}): DW_OP_constu 0x4048f5c3)
; CHECK-NEXT: DW_AT_name {{.*}}"f"
source_filename = "test.c"
diff --git a/llvm/test/DebugInfo/X86/implicit_value-double.ll b/llvm/test/DebugInfo/X86/implicit_value-double.ll
new file mode 100644
index 000000000000..3c14c7dfefce
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/implicit_value-double.ll
@@ -0,0 +1,66 @@
+;; This test checks for emission of DW_OP_implicit_value operation
+;; for double type.
+
+; RUN: llc -debugger-tune=gdb -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
+
+; CHECK: .debug_info contents:
+; CHECK: DW_TAG_variable
+; CHECK-NEXT: DW_AT_location ({{.*}}
+; CHECK-NEXT: [{{.*}}): DW_OP_implicit_value 0x8 0x1f 0x85 0xeb 0x51 0xb8 0x1e 0x09 0x40)
+; CHECK-NEXT: DW_AT_name ("d")
+
+;; Generated from: clang -ggdb -O1
+;;int main() {
+;; double d = 3.14;
+;; printf("dummy\n");
+;; d *= d;
+;; return 0;
+;;}
+
+; ModuleID = 'implicit_value-double.c'
+source_filename = "implicit_value-double.c"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at str = private unnamed_addr constant [6 x i8] c"dummy\00", align 1
+
+; Function Attrs: nofree nounwind uwtable
+define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 {
+entry:
+ call void @llvm.dbg.value(metadata double 3.140000e+00, metadata !12, metadata !DIExpression()), !dbg !14
+ %puts = call i32 @puts(i8* nonnull dereferenceable(1) getelementptr inbounds ([6 x i8], [6 x i8]* @str, i64 0, i64 0)), !dbg !15
+ call void @llvm.dbg.value(metadata double undef, metadata !12, metadata !DIExpression()), !dbg !14
+ ret i32 0, !dbg !16
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+; Function Attrs: nofree nounwind
+declare i32 @puts(i8* nocapture readonly) local_unnamed_addr #2
+
+attributes #0 = { nofree nounwind uwtable }
+attributes #1 = { nounwind readnone speculatable willreturn }
+attributes #2 = { nofree nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!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)
+!1 = !DIFile(filename: "implicit_value-double.c", directory: "/home/")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 11.0.0"}
+!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "d", scope: !7, file: !1, line: 2, type: !13)
+!13 = !DIBasicType(name: "double", size: 64, encoding: DW_ATE_float)
+!14 = !DILocation(line: 0, scope: !7)
+!15 = !DILocation(line: 3, column: 2, scope: !7)
+!16 = !DILocation(line: 5, column: 2, scope: !7)
diff --git a/llvm/test/DebugInfo/X86/implicit_value-float.ll b/llvm/test/DebugInfo/X86/implicit_value-float.ll
new file mode 100644
index 000000000000..8c51b4948177
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/implicit_value-float.ll
@@ -0,0 +1,65 @@
+;; This test checks for emission of DW_OP_implicit_value operation
+;; for float type.
+
+; RUN: llc -debugger-tune=gdb -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
+
+; CHECK: .debug_info contents:
+; CHECK: DW_TAG_variable
+; CHECK-NEXT: DW_AT_location ({{.*}}
+; CHECK-NEXT: [{{.*}}): DW_OP_implicit_value 0x4 0xc3 0xf5 0x48 0x40)
+; CHECK-NEXT: DW_AT_name ("f")
+
+;; Generated from: clang -ggdb -O1
+;;int main() {
+;; float f = 3.14f;
+;; printf("dummy\n");
+;; f *= f;
+;; return 0;
+;;}
+; ModuleID = 'implicit_value-float.c'
+source_filename = "implicit_value-float.c"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at str = private unnamed_addr constant [6 x i8] c"dummy\00", align 1
+
+; Function Attrs: nofree nounwind uwtable
+define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 {
+entry:
+ call void @llvm.dbg.value(metadata float 0x40091EB860000000, metadata !12, metadata !DIExpression()), !dbg !14
+ %puts = call i32 @puts(i8* nonnull dereferenceable(1) getelementptr inbounds ([6 x i8], [6 x i8]* @str, i64 0, i64 0)), !dbg !15
+ call void @llvm.dbg.value(metadata float undef, metadata !12, metadata !DIExpression()), !dbg !14
+ ret i32 0, !dbg !16
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+; Function Attrs: nofree nounwind
+declare i32 @puts(i8* nocapture readonly) local_unnamed_addr #2
+
+attributes #0 = { nofree nounwind uwtable }
+attributes #1 = { nounwind readnone speculatable willreturn }
+attributes #2 = { nofree nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!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)
+!1 = !DIFile(filename: "implicit_value-float.c", directory: "/home/")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 11.0.0"}
+!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "f", scope: !7, file: !1, line: 2, type: !13)
+!13 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+!14 = !DILocation(line: 0, scope: !7)
+!15 = !DILocation(line: 3, column: 2, scope: !7)
+!16 = !DILocation(line: 5, column: 2, scope: !7)
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