[DebugInfo][NewGVN] Salvage debug values of trivially dead instructions (#149304)

fix #149301

Author: Apochens

llvm/lib/Transforms/Scalar/NewGVN.cpp

@@ -3045,6 +3045,7 @@ std::pair<unsigned, unsigned> NewGVN::assignDFSNumbers(BasicBlock *B,
     if (isInstructionTriviallyDead(&I, TLI)) {
       InstrDFS[&I] = 0;
       LLVM_DEBUG(dbgs() << "Skipping trivially dead instruction " << I << "\n");
+      salvageDebugInfo(I);
       markInstructionForDeletion(&I);
       continue;
     }

llvm/test/Transforms/NewGVN/salvage-trivially-dead-inst.ll

@@ -0,0 +1,33 @@
+; RUN: opt -passes=newgvn -S %s | FileCheck %s
+
+; Check that assignDFSNumbers() in NewGVN salvages the debug values of the
+; trivially dead instructions that are marked for deletion.
+
+; CHECK: #dbg_value(i8 %tmp, [[META11:![0-9]+]], !DIExpression(DW_OP_constu, 8, DW_OP_eq, DW_OP_stack_value), [[META26:![0-9]+]])
+; CHECK: [[META11]] = !DILocalVariable(name: "2"
+; CHECK: [[META26]] = !DILocation(line: 2
+
+define void @test13() !dbg !5 {
+entry:
+  %tmp = load i8, ptr null, align 1
+  %tmp2 = icmp eq i8 %tmp, 8, !dbg !13
+    #dbg_value(i1 %tmp2, !11, !DIExpression(), !13)
+  ret void
+}
+
+!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 3}
+!3 = !{i32 2}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "test13", linkageName: "test13", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+!6 = !DISubroutineType(types: !7)
+!7 = !{}
+!8 = !{!11}
+!10 = !DIBasicType(name: "ty8", size: 8, encoding: DW_ATE_unsigned)
+!11 = !DILocalVariable(name: "2", scope: !5, file: !1, line: 2, type: !10)
+!13 = !DILocation(line: 2, column: 1, scope: !5)