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Do not emit right shift by 0 in DWARF expressions #162738

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Merged
merged 1 commit into from
Oct 10, 2025
Merged

Do not emit right shift by 0 in DWARF expressions #162738

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10 changes: 6 additions & 4 deletions llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -587,10 +587,12 @@ bool DwarfExpression::addExpression(
emitUnsigned(LeftShift);
emitOp(dwarf::DW_OP_shl);
}
emitOp(dwarf::DW_OP_constu);
emitUnsigned(RightShift);
emitOp(OpNum == dwarf::DW_OP_LLVM_extract_bits_sext ? dwarf::DW_OP_shra
: dwarf::DW_OP_shr);
if (RightShift) {
emitOp(dwarf::DW_OP_constu);
emitUnsigned(RightShift);
emitOp(OpNum == dwarf::DW_OP_LLVM_extract_bits_sext ? dwarf::DW_OP_shra
: dwarf::DW_OP_shr);
}

// The value is now at the top of the stack, so set the location to
// implicit so that we get a stack_value at the end.
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5 changes: 5 additions & 0 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 @@ -67,13 +67,16 @@ entry:
; 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")
; CHECK: DW_AT_location (DW_OP_fbreg -4, DW_OP_deref_size 0x8, DW_OP_stack_value)
; CHECK: DW_AT_name ("q")

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
tail call void @llvm.dbg.declare(metadata ptr %0, metadata !33, metadata !DIExpression(DW_OP_LLVM_extract_bits_zext, 0, 64)), !dbg !30
ret i32 0, !dbg !30
}

Expand Down Expand Up @@ -116,3 +119,5 @@ declare void @llvm.dbg.value(metadata, metadata, metadata)
!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)
!33 = !DILocalVariable(name: "q", scope: !28, file: !3, type: !34)
!34 = !DIBasicType(name: "uint64_t", size: 64, encoding: DW_ATE_unsigned)