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[DebugInfo] Use DW_OP_deref_size for DW_OP_LLVM_extract_bits #97609

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Merged
merged 1 commit into from
Jul 11, 2024
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[DebugInfo] Use DW_OP_deref_size for DW_OP_LLVM_extract_bits #97609

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10 changes: 7 additions & 3 deletions llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -552,9 +552,13 @@ bool DwarfExpression::addExpression(
unsigned SizeInBits = Op->getArg(1);
unsigned BitOffset = Op->getArg(0);

// If we have a memory location then dereference to get the value
if (isMemoryLocation())
emitOp(dwarf::DW_OP_deref);
// If we have a memory location then dereference to get the value, though
// we have to make sure we don't dereference any bytes past the end of the
// object.
if (isMemoryLocation()) {
emitOp(dwarf::DW_OP_deref_size);
emitUnsigned(alignTo(BitOffset + SizeInBits, 8) / 8);
}
Comment on lines +558 to +561
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I think ideally we'd only use DW_OP_deref_size if DW_OP_deref will actually dereference too many bytes, but that's a minor point.


// Extract the bits by a shift left (to shift out the bits after what we
// want to extract) followed by shift right (to shift the bits to position
Expand Down
30 changes: 28 additions & 2 deletions llvm/test/DebugInfo/X86/DW_OP_LLVM_extract_bits.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -8,10 +8,10 @@
; CHECK-LABEL: DW_TAG_subprogram
; CHECK: DW_AT_name ("test1")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_fbreg -1, DW_OP_deref, DW_OP_constu 0x3d, DW_OP_shl, DW_OP_constu 0x3d, DW_OP_shr, DW_OP_stack_value)
; CHECK: DW_AT_location (DW_OP_fbreg -1, DW_OP_deref_size 0x1, DW_OP_constu 0x3d, DW_OP_shl, DW_OP_constu 0x3d, DW_OP_shr, DW_OP_stack_value)
; CHECK: DW_AT_name ("x")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_fbreg -1, DW_OP_deref, DW_OP_constu 0x39, DW_OP_shl, DW_OP_constu 0x3c, DW_OP_shra, DW_OP_stack_value)
; CHECK: DW_AT_location (DW_OP_fbreg -1, DW_OP_deref_size 0x1, DW_OP_constu 0x39, DW_OP_shl, DW_OP_constu 0x3c, DW_OP_shra, DW_OP_stack_value)
; CHECK: DW_AT_name ("y")

define i32 @test1() !dbg !13 {
Expand Down Expand Up @@ -56,6 +56,27 @@ entry:
ret i64 %0, !dbg !26
}

; CHECK-LABEL: DW_TAG_subprogram
; CHECK: DW_AT_name ("test4")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_fbreg -4, DW_OP_deref_size 0x4, DW_OP_constu 0x20, DW_OP_shl, DW_OP_constu 0x3f, DW_OP_shr, DW_OP_stack_value)
; CHECK: DW_AT_name ("x")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_fbreg -4, DW_OP_deref_size 0x4, DW_OP_constu 0x20, DW_OP_shl, DW_OP_constu 0x21, DW_OP_shra, DW_OP_stack_value)
; CHECK: DW_AT_name ("y")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_fbreg -4, DW_OP_plus_uconst 0x3, DW_OP_deref_size 0x1, DW_OP_constu 0x38, DW_OP_shl, DW_OP_constu 0x39, DW_OP_shr, DW_OP_stack_value)
; CHECK: DW_AT_name ("z")

define i32 @test4() !dbg !28 {
entry:
%0 = alloca i32, align 4
tail call void @llvm.dbg.declare(metadata ptr %0, metadata !29, metadata !DIExpression(DW_OP_LLVM_extract_bits_zext, 31, 1)), !dbg !30
tail call void @llvm.dbg.declare(metadata ptr %0, metadata !31, metadata !DIExpression(DW_OP_LLVM_extract_bits_sext, 1, 31)), !dbg !30
tail call void @llvm.dbg.declare(metadata ptr %0, metadata !32, metadata !DIExpression(DW_OP_plus_uconst, 3, DW_OP_LLVM_extract_bits_zext, 1, 7)), !dbg !30
ret i32 0, !dbg !30
}

declare void @llvm.dbg.declare(metadata, metadata, metadata)
declare void @llvm.dbg.value(metadata, metadata, metadata)

Expand Down Expand Up @@ -90,3 +111,8 @@ declare void @llvm.dbg.value(metadata, metadata, metadata)
!25 = !DILocalVariable(name: "x", scope: !24, file: !3, type: !9)
!26 = !DILocation(line: 0, scope: !24)
!27 = !DILocalVariable(name: "y", scope: !24, file: !3, type: !19)
!28 = distinct !DISubprogram(name: "test4", linkageName: "test4", scope: !3, file: !3, type: !14, spFlags: DISPFlagDefinition, unit: !2)
!29 = !DILocalVariable(name: "x", scope: !28, file: !3, type: !9)
!30 = !DILocation(line: 0, scope: !28)
!31 = !DILocalVariable(name: "y", scope: !28, file: !3, type: !19)
!32 = !DILocalVariable(name: "z", scope: !28, file: !3, type: !9)
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