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[DebugInfo][LoopDistribute] Salvage debug values using dead instructions in the distributed loops #137124

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Merged
merged 4 commits into from
May 12, 2025
Merged

[DebugInfo][LoopDistribute] Salvage debug values using dead instructions in the distributed loops #137124

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9bc06df
Fix #136532: salvage debug values in the distributed loops
Apochens Apr 24, 2025
8b6aabe
add the check discription to the regression test
Apochens Apr 24, 2025
c6cd1b6
simplify the regression test
Apochens May 6, 2025
0da24af
refine test
Apochens May 6, 2025
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2 changes: 2 additions & 0 deletions llvm/lib/Transforms/Scalar/LoopDistribute.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,7 @@
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/LoopVersioning.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
Expand Down Expand Up @@ -224,6 +225,7 @@ class InstPartition {
// Delete the instructions backwards, as it has a reduced likelihood of
// having to update as many def-use and use-def chains.
for (auto *Inst : reverse(Unused)) {
salvageDebugInfo(*Inst);
if (!Inst->use_empty())
Inst->replaceAllUsesWith(PoisonValue::get(Inst->getType()));
Inst->eraseFromParent();
Expand Down
100 changes: 100 additions & 0 deletions llvm/test/Transforms/LoopDistribute/salvage-dbg-values-in-distributed-loops.ll
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@@ -0,0 +1,100 @@
; RUN: opt -passes=loop-distribute -enable-loop-distribute -S < %s | FileCheck %s

; Check that removeUnusedInsts() salvages `dbg_value`s which use dead
; instructions in the distributed loops.

define void @f(ptr noalias %a, ptr noalias %c, ptr noalias %d) !dbg !5 {
; CHECK-LABEL: define void @f(
; CHECK-SAME: ptr noalias [[A:%.*]], ptr noalias [[C:%.*]], ptr noalias [[D:%.*]])

entry:
br label %for.body, !dbg !21

for.body: ; preds = %for.body, %entry
%ind = phi i64 [ 0, %entry ], [ %add, %for.body ], !dbg !22
#dbg_value(i64 %ind, !9, !DIExpression(), !22)
%add = add nuw nsw i64 %ind, 1, !dbg !23
#dbg_value(i64 %add, !11, !DIExpression(), !23)


; CHECK-LABEL: for.body.ldist1:
; CHECK: #dbg_value(!DIArgList(ptr [[D]], i64 [[IND_LDIST1:%.*]]), [[META16:![0-9]+]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_constu, 4, DW_OP_mul, DW_OP_plus, DW_OP_stack_value), [[META28:![0-9]+]])
; CHECK: #dbg_value(!DIArgList(ptr [[C]], i64 [[IND_LDIST1]]), [[META18:![0-9]+]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_constu, 4, DW_OP_mul, DW_OP_plus, DW_OP_stack_value), [[META30:![0-9]+]])
;
%arrayidxA = getelementptr inbounds i32, ptr %a, i64 %ind, !dbg !24
#dbg_value(ptr %arrayidxA, !12, !DIExpression(), !24)
%loadA = load i32, ptr %arrayidxA, align 4, !dbg !25
#dbg_value(i32 %loadA, !13, !DIExpression(), !25)
%arrayidxA_plus_4 = getelementptr inbounds i32, ptr %a, i64 %add, !dbg !26
#dbg_value(ptr %arrayidxA_plus_4, !15, !DIExpression(), !26)
store i32 %loadA, ptr %arrayidxA_plus_4, align 4, !dbg !27

; CHECK-LABEL: for.body:
; CHECK: #dbg_value(!DIArgList(ptr [[A]], i64 [[IND:%.*]]), [[META12:![0-9]+]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_constu, 4, DW_OP_mul, DW_OP_plus, DW_OP_stack_value), [[DBG24:![0-9]+]])
; CHECK: #dbg_value(!DIArgList(ptr [[A]], i64 [[ADD:%.*]]), [[META15:![0-9]+]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_constu, 4, DW_OP_mul, DW_OP_plus, DW_OP_stack_value), [[DBG26:![0-9]+]])
;
%arrayidxD = getelementptr inbounds i32, ptr %d, i64 %ind, !dbg !28
#dbg_value(ptr %arrayidxD, !16, !DIExpression(), !28)
%loadD = load i32, ptr %arrayidxD, align 4, !dbg !29
#dbg_value(i32 %loadD, !17, !DIExpression(), !29)
%arrayidxC = getelementptr inbounds i32, ptr %c, i64 %ind, !dbg !30
#dbg_value(ptr %arrayidxC, !18, !DIExpression(), !30)
store i32 %loadD, ptr %arrayidxC, align 4, !dbg !31

%exitcond = icmp eq i64 %add, 20, !dbg !32
#dbg_value(i1 %exitcond, !19, !DIExpression(), !32)
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@OCHyams OCHyams May 6, 2025

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Do we need all the dbg_values? I feel like we probably get the same coverage (and a simpler test) if there's just one dbg_value?

nit: please can you indent the dbg_values by two spaces? that's how LLVM prints them, and it's easier to read that way.

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@Apochens Apochens May 6, 2025

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Now there are only two dbg_values left in the test. Each one is used to test the salvage in one of the distributed loops. Meanwhile, the DILocalVariables has also been shrunk, keeping the ones used in the checks.

br i1 %exitcond, label %for.end, label %for.body, !dbg !33

for.end: ; preds = %for.body
ret void, !dbg !34
}

!llvm.dbg.cu = !{!0}
!llvm.debugify = !{!2, !3}
!llvm.module.flags = !{!4}

!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
!1 = !DIFile(filename: "temp.ll", directory: "/")
!2 = !{i32 14}
!3 = !{i32 9}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = distinct !DISubprogram(name: "f", linkageName: "f", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
!6 = !DISubroutineType(types: !7)
!7 = !{}
!8 = !{!9, !11, !12, !13, !15, !16, !17, !18, !19}
!9 = !DILocalVariable(name: "1", scope: !5, file: !1, line: 2, type: !10)
!10 = !DIBasicType(name: "ty64", size: 64, encoding: DW_ATE_unsigned)
!11 = !DILocalVariable(name: "2", scope: !5, file: !1, line: 3, type: !10)
!12 = !DILocalVariable(name: "3", scope: !5, file: !1, line: 4, type: !10)
!13 = !DILocalVariable(name: "4", scope: !5, file: !1, line: 5, type: !14)
!14 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
!15 = !DILocalVariable(name: "5", scope: !5, file: !1, line: 6, type: !10)
!16 = !DILocalVariable(name: "6", scope: !5, file: !1, line: 8, type: !10)
!17 = !DILocalVariable(name: "7", scope: !5, file: !1, line: 9, type: !14)
!18 = !DILocalVariable(name: "8", scope: !5, file: !1, line: 10, type: !10)
!19 = !DILocalVariable(name: "9", scope: !5, file: !1, line: 12, type: !20)
!20 = !DIBasicType(name: "ty8", size: 8, encoding: DW_ATE_unsigned)
!21 = !DILocation(line: 1, column: 1, scope: !5)
!22 = !DILocation(line: 2, column: 1, scope: !5)
!23 = !DILocation(line: 3, column: 1, scope: !5)
!24 = !DILocation(line: 4, column: 1, scope: !5)
!25 = !DILocation(line: 5, column: 1, scope: !5)
!26 = !DILocation(line: 6, column: 1, scope: !5)
!27 = !DILocation(line: 7, column: 1, scope: !5)
!28 = !DILocation(line: 8, column: 1, scope: !5)
!29 = !DILocation(line: 9, column: 1, scope: !5)
!30 = !DILocation(line: 10, column: 1, scope: !5)
!31 = !DILocation(line: 11, column: 1, scope: !5)
!32 = !DILocation(line: 12, column: 1, scope: !5)
!33 = !DILocation(line: 13, column: 1, scope: !5)
!34 = !DILocation(line: 14, column: 1, scope: !5)
;.
; CHECK: [[META12]] = !DILocalVariable(name: "3"
; CHECK: [[META15]] = !DILocalVariable(name: "5"
; CHECK: [[META16]] = !DILocalVariable(name: "6"
; CHECK: [[META18]] = !DILocalVariable(name: "8"
; CHECK: [[DBG24]] = !DILocation(line: 4, column: 1
; CHECK: [[DBG26]] = !DILocation(line: 6, column: 1
; CHECK: [[META28]] = !DILocation(line: 8, column: 1
; CHECK: [[META30]] = !DILocation(line: 10, column: 1
;.