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

Fix #136532 .

Author: Apochens

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();

llvm/test/Transforms/LoopDistribute/salvage-dbg-values-in-distributed-loops.ll

@@ -0,0 +1,77 @@
+; 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
+  %add = add nuw nsw i64 %ind, 1, !dbg !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]+]])
+;
+  %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
+  %arrayidxA_plus_4 = getelementptr inbounds i32, ptr %a, i64 %add, !dbg !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]+]])
+;
+  %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
+  %arrayidxC = getelementptr inbounds i32, ptr %c, i64 %ind, !dbg !30
+  store i32 %loadD, ptr %arrayidxC, align 4, !dbg !31
+
+  %exitcond = icmp eq i64 %add, 20, !dbg !32
+  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 = !{!12, !16}
+!10 = !DIBasicType(name: "ty64", size: 64, encoding: DW_ATE_unsigned)
+!12 = !DILocalVariable(name: "3", scope: !5, file: !1, line: 4, type: !10)
+!16 = !DILocalVariable(name: "6", scope: !5, file: !1, line: 8, type: !10)
+!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: [[META16]] = !DILocalVariable(name: "6"
+; CHECK: [[DBG24]] = !DILocation(line: 4, column: 1
+; CHECK: [[META28]] = !DILocation(line: 8, column: 1
+;.