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

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

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Fix #136532 .

@Apochens Apochens requested review from jryans, SLTozer and OCHyams April 24, 2025 06:40
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llvmbot commented Apr 24, 2025

@llvm/pr-subscribers-llvm-transforms

Author: Shan Huang (Apochens)

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Fix #136532 .

Full diff: https://github.com/llvm/llvm-project/pull/137124.diff

2 Files Affected:

  • (modified) llvm/lib/Transforms/Scalar/LoopDistribute.cpp (+2)
  • (added) llvm/test/Transforms/LoopDistribute/salvage-dbg-values-in-distributed-loops.ll (+159)
diff --git a/llvm/lib/Transforms/Scalar/LoopDistribute.cpp b/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
index e10d0c0defd96..0ac1a15981770 100644
--- a/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
@@ -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"
@@ -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();
diff --git a/llvm/test/Transforms/LoopDistribute/salvage-dbg-values-in-distributed-loops.ll b/llvm/test/Transforms/LoopDistribute/salvage-dbg-values-in-distributed-loops.ll
new file mode 100644
index 0000000000000..9927d796a3deb
--- /dev/null
+++ b/llvm/test/Transforms/LoopDistribute/salvage-dbg-values-in-distributed-loops.ll
@@ -0,0 +1,159 @@
+; 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 %b, ptr noalias %c, ptr noalias %d, ptr noalias %e) !dbg !5 {
+; CHECK-LABEL: define void @f(
+; CHECK-SAME: ptr noalias [[A:%.*]], ptr noalias [[B:%.*]], ptr noalias [[C:%.*]], ptr noalias [[D:%.*]], ptr noalias [[E:%.*]])
+
+; CHECK:       for.body.ldist1:
+; CHECK-NEXT:    [[IND_LDIST1:%.*]] = phi i64 [ 0, %[[ENTRY_SPLIT_LDIST1:.*]] ], [ [[ADD_LDIST1:%.*]], %for.body.ldist1 ], !dbg [[DBG28:![0-9]+]]
+
+; CHECK:           store i32
+; CHECK-NEXT:      #dbg_value(!DIArgList(ptr [[D]], i64 [[IND_LDIST1]]), [[META19:![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), [[META37:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(i32 poison, [[META20:![0-9]+]], !DIExpression(), [[META38:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(!DIArgList(ptr [[E]], i64 [[IND_LDIST1]]), [[META21:![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), [[META39:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(i32 poison, [[META22:![0-9]+]], !DIExpression(), [[META40:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(!DIArgList(i32 poison, i32 poison), [[META23:![0-9]+]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_mul, DW_OP_stack_value), [[META41:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(!DIArgList(ptr [[C]], i64 [[IND_LDIST1]]), [[META24:![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), [[META42:![0-9]+]])
+; CHECK-NEXT:    [[EXITCOND_LDIST1:%.*]] = icmp eq i64 [[ADD_LDIST1]], 20, !dbg [[DBG43:![0-9]+]]
+; CHECK-NEXT:      #dbg_value(i1 [[EXITCOND_LDIST1]], [[META25:![0-9]+]], !DIExpression(), [[DBG43]])
+; CHECK-NEXT:    br i1 [[EXITCOND_LDIST1]], label %[[ENTRY_SPLIT:.*]], label %for.body.ldist1, !dbg [[DBG44:![0-9]+]]
+
+; CHECK:       for.body:
+; CHECK-NEXT:    [[IND:%.*]] = phi i64 [ 0, %[[ENTRY_SPLIT:.*]] ], [ [[ADD:%.*]], %for.body ], !dbg [[DBG28]]
+; CHECK-NEXT:      #dbg_value(i64 [[IND]], [[META9:![0-9]+]], !DIExpression(), [[DBG28]])
+; CHECK-NEXT:      #dbg_value(!DIArgList(ptr [[A]], i64 [[IND]]), [[META11:![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), [[DBG29:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(i32 poison, [[META12:![0-9]+]], !DIExpression(), [[DBG30:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(!DIArgList(ptr [[B]], i64 [[IND]]), [[META14:![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), [[DBG31:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(i32 poison, [[META15:![0-9]+]], !DIExpression(), [[DBG32:![0-9]+]])
+; CHECK-NEXT:      #dbg_value(!DIArgList(i32 poison, i32 poison), [[META16:![0-9]+]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_mul, DW_OP_stack_value), [[DBG33:![0-9]+]])
+; CHECK-NEXT:    [[ADD]] = add nuw nsw i64 [[IND]], 1, !dbg [[DBG34:![0-9]+]]
+; CHECK-NEXT:      #dbg_value(i64 [[ADD]], [[META17:![0-9]+]], !DIExpression(), [[DBG34]])
+; CHECK-NEXT:      #dbg_value(!DIArgList(ptr [[A]], i64 [[ADD]]), [[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), [[DBG35:![0-9]+]])
+;
+entry:
+  br label %for.body, !dbg !27
+
+for.body:                                         ; preds = %for.body, %entry
+  %ind = phi i64 [ 0, %entry ], [ %add, %for.body ], !dbg !28
+  #dbg_value(i64 %ind, !9, !DIExpression(), !28)
+  %arrayidxA = getelementptr inbounds i32, ptr %a, i64 %ind, !dbg !29
+  #dbg_value(ptr %arrayidxA, !11, !DIExpression(), !29)
+  %loadA = load i32, ptr %arrayidxA, align 4, !dbg !30
+  #dbg_value(i32 %loadA, !12, !DIExpression(), !30)
+  %arrayidxB = getelementptr inbounds i32, ptr %b, i64 %ind, !dbg !31
+  #dbg_value(ptr %arrayidxB, !14, !DIExpression(), !31)
+  %loadB = load i32, ptr %arrayidxB, align 4, !dbg !32
+  #dbg_value(i32 %loadB, !15, !DIExpression(), !32)
+  %mulA = mul i32 %loadB, %loadA, !dbg !33
+  #dbg_value(i32 %mulA, !16, !DIExpression(), !33)
+  %add = add nuw nsw i64 %ind, 1, !dbg !34
+  #dbg_value(i64 %add, !17, !DIExpression(), !34)
+  %arrayidxA_plus_4 = getelementptr inbounds i32, ptr %a, i64 %add, !dbg !35
+  #dbg_value(ptr %arrayidxA_plus_4, !18, !DIExpression(), !35)
+  store i32 %mulA, ptr %arrayidxA_plus_4, align 4, !dbg !36
+  %arrayidxD = getelementptr inbounds i32, ptr %d, i64 %ind, !dbg !37
+  #dbg_value(ptr %arrayidxD, !19, !DIExpression(), !37)
+  %loadD = load i32, ptr %arrayidxD, align 4, !dbg !38
+  #dbg_value(i32 %loadD, !20, !DIExpression(), !38)
+  %arrayidxE = getelementptr inbounds i32, ptr %e, i64 %ind, !dbg !39
+  #dbg_value(ptr %arrayidxE, !21, !DIExpression(), !39)
+  %loadE = load i32, ptr %arrayidxE, align 4, !dbg !40
+  #dbg_value(i32 %loadE, !22, !DIExpression(), !40)
+  %mulC = mul i32 %loadD, %loadE, !dbg !41
+  #dbg_value(i32 %mulC, !23, !DIExpression(), !41)
+  %arrayidxC = getelementptr inbounds i32, ptr %c, i64 %ind, !dbg !42
+  #dbg_value(ptr %arrayidxC, !24, !DIExpression(), !42)
+  store i32 %mulC, ptr %arrayidxC, align 4, !dbg !43
+  %exitcond = icmp eq i64 %add, 20, !dbg !44
+  #dbg_value(i1 %exitcond, !25, !DIExpression(), !44)
+  br i1 %exitcond, label %for.end, label %for.body, !dbg !45
+
+for.end:                                          ; preds = %for.body
+  ret void, !dbg !46
+}
+
+!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: "/app/example.ll", directory: "/")
+!2 = !{i32 20}
+!3 = !{i32 15}
+!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, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25}
+!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: !13)
+!13 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+!14 = !DILocalVariable(name: "4", scope: !5, file: !1, line: 5, type: !10)
+!15 = !DILocalVariable(name: "5", scope: !5, file: !1, line: 6, type: !13)
+!16 = !DILocalVariable(name: "6", scope: !5, file: !1, line: 7, type: !13)
+!17 = !DILocalVariable(name: "7", scope: !5, file: !1, line: 8, type: !10)
+!18 = !DILocalVariable(name: "8", scope: !5, file: !1, line: 9, type: !10)
+!19 = !DILocalVariable(name: "9", scope: !5, file: !1, line: 11, type: !10)
+!20 = !DILocalVariable(name: "10", scope: !5, file: !1, line: 12, type: !13)
+!21 = !DILocalVariable(name: "11", scope: !5, file: !1, line: 13, type: !10)
+!22 = !DILocalVariable(name: "12", scope: !5, file: !1, line: 14, type: !13)
+!23 = !DILocalVariable(name: "13", scope: !5, file: !1, line: 15, type: !13)
+!24 = !DILocalVariable(name: "14", scope: !5, file: !1, line: 16, type: !10)
+!25 = !DILocalVariable(name: "15", scope: !5, file: !1, line: 18, type: !26)
+!26 = !DIBasicType(name: "ty8", size: 8, encoding: DW_ATE_unsigned)
+!27 = !DILocation(line: 1, column: 1, scope: !5)
+!28 = !DILocation(line: 2, column: 1, scope: !5)
+!29 = !DILocation(line: 3, column: 1, scope: !5)
+!30 = !DILocation(line: 4, column: 1, scope: !5)
+!31 = !DILocation(line: 5, column: 1, scope: !5)
+!32 = !DILocation(line: 6, column: 1, scope: !5)
+!33 = !DILocation(line: 7, column: 1, scope: !5)
+!34 = !DILocation(line: 8, column: 1, scope: !5)
+!35 = !DILocation(line: 9, column: 1, scope: !5)
+!36 = !DILocation(line: 10, column: 1, scope: !5)
+!37 = !DILocation(line: 11, column: 1, scope: !5)
+!38 = !DILocation(line: 12, column: 1, scope: !5)
+!39 = !DILocation(line: 13, column: 1, scope: !5)
+!40 = !DILocation(line: 14, column: 1, scope: !5)
+!41 = !DILocation(line: 15, column: 1, scope: !5)
+!42 = !DILocation(line: 16, column: 1, scope: !5)
+!43 = !DILocation(line: 17, column: 1, scope: !5)
+!44 = !DILocation(line: 18, column: 1, scope: !5)
+!45 = !DILocation(line: 19, column: 1, scope: !5)
+!46 = !DILocation(line: 20, column: 1, scope: !5)
+;.
+; CHECK: [[META9]] = !DILocalVariable(name: "1",
+; CHECK: [[META11]] = !DILocalVariable(name: "2",
+; CHECK: [[META12]] = !DILocalVariable(name: "3",
+; CHECK: [[META14]] = !DILocalVariable(name: "4",
+; CHECK: [[META15]] = !DILocalVariable(name: "5",
+; CHECK: [[META16]] = !DILocalVariable(name: "6",
+; CHECK: [[META17]] = !DILocalVariable(name: "7",
+; CHECK: [[META18]] = !DILocalVariable(name: "8",
+; CHECK: [[META19]] = !DILocalVariable(name: "9",
+; CHECK: [[META20]] = !DILocalVariable(name: "10",
+; CHECK: [[META21]] = !DILocalVariable(name: "11",
+; CHECK: [[META22]] = !DILocalVariable(name: "12",
+; CHECK: [[META23]] = !DILocalVariable(name: "13",
+; CHECK: [[META24]] = !DILocalVariable(name: "14",
+; CHECK: [[META25]] = !DILocalVariable(name: "15",
+; CHECK: [[DBG28]] = !DILocation(line: 2, column: 1,
+; CHECK: [[DBG29]] = !DILocation(line: 3, column: 1,
+; CHECK: [[DBG30]] = !DILocation(line: 4, column: 1,
+; CHECK: [[DBG31]] = !DILocation(line: 5, column: 1,
+; CHECK: [[DBG33]] = !DILocation(line: 7, column: 1,
+; CHECK: [[DBG34]] = !DILocation(line: 8, column: 1,
+; CHECK: [[DBG35]] = !DILocation(line: 9, column: 1,
+; CHECK: [[META37]] = !DILocation(line: 11, column: 1,
+; CHECK: [[META39]] = !DILocation(line: 13, column: 1,
+; CHECK: [[META40]] = !DILocation(line: 14, column: 1,
+; CHECK: [[META41]] = !DILocation(line: 15, column: 1,
+; CHECK: [[META42]] = !DILocation(line: 16, column: 1,
+; CHECK: [[DBG43]] = !DILocation(line: 18, column: 1,
+; CHECK: [[DBG44]] = !DILocation(line: 19, column: 1,
+;.

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Apochens commented May 5, 2025

Hi @OCHyams , just following up on this PR. It’s been open for a few days and I’d appreciate your feedback when you get a chance. Thanks!

OCHyams
OCHyams reviewed May 6, 2025
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Sorry @Apochens, it got lost in the github notifications.

Would it be possible to reduce the test case a bit? If the dbg_value s are all testing the same code path then just one is sufficient for the test. And if we can reduce the number of instructions too, that will help future maintainers understand what's going on.

Otherwise SGTM

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Apochens commented May 6, 2025

Thanks @OCHyams ! I've refined the regression test by removing some instructions and checks in it. As a result, the test is more concise now.

OCHyams
OCHyams reviewed May 6, 2025
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llvm/test/Transforms/LoopDistribute/salvage-dbg-values-in-distributed-loops.ll Outdated
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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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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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.

OCHyams
OCHyams approved these changes May 6, 2025
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Thanks! LGTM

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@OCHyams OCHyams OCHyams approved these changes

@jryans jryans Awaiting requested review from jryans

@SLTozer SLTozer Awaiting requested review from SLTozer

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[DebugInfo][LoopDistribute] Removing instructions without salvaging the debug variable Info
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