[InstCombine] Salvage debug info during initial DCE

InstCombine salvages debug info for every instruction it erases from its
worklist, but it wasn't doing it during its initial DCE when populating
its worklist. This fixes that.

This should help improve availability of 'this' in optimized debug info
when casts are necessary.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@318320 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index dad066a..f272f82 100644 (file)
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3113,6 +3113,7 @@ static bool AddReachableCodeToWorklist(BasicBlock *BB, const DataLayout &DL,
       if (isInstructionTriviallyDead(Inst, TLI)) {
         ++NumDeadInst;
         DEBUG(dbgs() << "IC: DCE: " << *Inst << '\n');
+        salvageDebugInfo(*Inst);
         Inst->eraseFromParent();
         MadeIRChange = true;
         continue;

diff --git a/test/Transforms/InstCombine/debuginfo-dce2.ll b/test/Transforms/InstCombine/debuginfo-dce2.ll
new file mode 100644 (file)
index 0000000..398f3c6
--- /dev/null
+++ b/test/Transforms/InstCombine/debuginfo-dce2.ll
@@ -0,0 +1,70 @@
+; RUN: opt -instcombine -S %s -o - | FileCheck %s
+
+; In this example, the cast from i8* to i32* becomes trivially dead. We should
+; salvage its debug info.
+
+; C source:
+; void use_as_void(void *);
+; void f(void *p) {
+;   int *q = (int *)p;
+;   use_as_void(q);
+; }
+
+; ModuleID = '<stdin>'
+source_filename = "t.c"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.11.25508"
+
+; Function Attrs: nounwind uwtable
+define void @f(i8* %p) !dbg !11 {
+entry:
+  call void @llvm.dbg.value(metadata i8* %p, metadata !16, metadata !DIExpression()), !dbg !18
+  %0 = bitcast i8* %p to i32*, !dbg !19
+  call void @llvm.dbg.value(metadata i32* %0, metadata !17, metadata !DIExpression()), !dbg !20
+  %1 = bitcast i32* %0 to i8*, !dbg !21
+  call void @use_as_void(i8* %1), !dbg !22
+  ret void, !dbg !23
+}
+
+; CHECK-LABEL: define void @f(i8* %p)
+; CHECK: call void @llvm.dbg.value(metadata i8* %p, metadata ![[P_VAR:[0-9]+]], metadata !DIExpression())
+; CHECK-NOT: bitcast
+; CHECK: call void @llvm.dbg.value(metadata i8* %p, metadata ![[Q_VAR:[0-9]+]], metadata !DIExpression())
+; CHECK-NOT: bitcast
+; CHECK ret void
+
+; CHECK: ![[P_VAR]] = !DILocalVariable(name: "p", {{.*}})
+; CHECK: ![[Q_VAR]] = !DILocalVariable(name: "q", {{.*}})
+
+declare void @use_as_void(i8*)
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!6, !7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 6.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3)
+!1 = !DIFile(filename: "t.c", directory: "C:\5Csrc\5Cllvm-project\5Cbuild", checksumkind: CSK_MD5, checksum: "56c40617ada23a8cccbd9a16bcec57af")
+!2 = !{}
+!3 = !{!4}
+!4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !5, size: 64)
+!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!6 = !{i32 2, !"CodeView", i32 1}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 1, !"wchar_size", i32 2}
+!9 = !{i32 7, !"PIC Level", i32 2}
+!10 = !{!"clang version 6.0.0 "}
+!11 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 2, type: !12, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !15)
+!12 = !DISubroutineType(types: !13)
+!13 = !{null, !14}
+!14 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!15 = !{!16, !17}
+!16 = !DILocalVariable(name: "p", arg: 1, scope: !11, file: !1, line: 2, type: !14)
+!17 = !DILocalVariable(name: "q", scope: !11, file: !1, line: 3, type: !4)
+!18 = !DILocation(line: 2, column: 14, scope: !11)
+!19 = !DILocation(line: 3, column: 12, scope: !11)
+!20 = !DILocation(line: 3, column: 8, scope: !11)
+!21 = !DILocation(line: 4, column: 15, scope: !11)
+!22 = !DILocation(line: 4, column: 3, scope: !11)
+!23 = !DILocation(line: 5, column: 1, scope: !11)