[DebugInfo@O2][Utils] Undef instead of delete dbg.values in helper func

Summary:
Related bug: https://bugs.llvm.org/show_bug.cgi?id=40648

Static helper function rewriteDebugUsers in Local.cpp deletes dbg.value
intrinsics when it cannot move or rewrite them, or salvage the deleted
instruction's value. It should instead undef them in this case.

This patch fixes that and I've added a test which covers the failing test
case in bz40648. I've updated the unit test Local.ReplaceAllDbgUsesWith
to check for this behaviour (and fixed a typo in the test which would
cause the old test to always pass).

Reviewers: aprantl, vsk, djtodoro, probinson

Reviewed By: vsk

Subscribers: hiraditya, llvm-commits

Tags: #debug-info, #llvm

Differential Revision: https://reviews.llvm.org/D70604

1 files changed, 76 insertions, 0 deletions

diff --git a/llvm/test/DebugInfo/X86/dbg-value-dropped-instcombine.ll b/llvm/test/DebugInfo/X86/dbg-value-dropped-instcombine.ll
new file mode 100644
index 00000000000..18e51b6fabd
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/dbg-value-dropped-instcombine.ll
@@ -0,0 +1,76 @@
+; RUN: opt -instcombine -S %s -o - | FileCheck %s
+
+; In pr40648 one of two dbg.values used to describe the variable bumble was
+; being dropped by instcombine. Test that both dbg.values survive instcombine.
+
+; $ clang -O0 -Xclang -disable-O0-optnone -g bees.c -emit-llvm -S -o - \
+;   | opt -opt-bisect-limit=10 -O2 -o -
+; $ cat bees.c
+; struct bees {
+;  int a;
+;  int b;
+; }
+
+; int global = 0;
+
+; struct bees foo(struct bees bumble)
+; {
+;   global = 1;
+;   int temp = bumble.a + bumble.b;
+;   return bumble;
+; }
+
+; CHECK: define dso_local i64 @foo
+; CHECK: @llvm.dbg.value({{.*}}, metadata ![[BEE:[0-9]+]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32)),
+; CHECK: @llvm.dbg.value(metadata i32 undef, metadata ![[BEE]], metadata !DIExpression(DW_OP_LLVM_fragment, 32, 32)),
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-unknown"
+
+@global = dso_local local_unnamed_addr global i32 0, align 4, !dbg !0
+
+define dso_local i64 @foo(i64 %bumble.coerce) local_unnamed_addr !dbg !11 {
+entry:
+  %bumble.sroa.0.0.extract.trunc = trunc i64 %bumble.coerce to i32
+  call void @llvm.dbg.value(metadata i32 %bumble.sroa.0.0.extract.trunc, metadata !18, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32)), !dbg !19
+  %bumble.sroa.3.0.extract.shift = lshr i64 %bumble.coerce, 32
+  %bumble.sroa.3.0.extract.trunc = trunc i64 %bumble.sroa.3.0.extract.shift to i32
+  call void @llvm.dbg.value(metadata i32 %bumble.sroa.3.0.extract.trunc, metadata !18, metadata !DIExpression(DW_OP_LLVM_fragment, 32, 32)), !dbg !19
+  store i32 1, i32* @global, align 4, !dbg !20
+  call void @llvm.dbg.value(metadata i32 undef, metadata !21, metadata !DIExpression()), !dbg !19
+  %retval.sroa.2.0.insert.ext = zext i32 %bumble.sroa.3.0.extract.trunc to i64, !dbg !22
+  %retval.sroa.2.0.insert.shift = shl i64 %retval.sroa.2.0.insert.ext, 32, !dbg !22
+  %retval.sroa.0.0.insert.ext = zext i32 %bumble.sroa.0.0.extract.trunc to i64, !dbg !22
+  %retval.sroa.0.0.insert.insert = or i64 %retval.sroa.2.0.insert.shift, %retval.sroa.0.0.insert.ext, !dbg !22
+  ret i64 %retval.sroa.0.0.insert.insert, !dbg !22
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "global", scope: !2, file: !3, line: 6, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 10.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None)
+!3 = !DIFile(filename: "bees.c", directory: "/")
+!4 = !{}
+!5 = !{!0}
+!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!7 = !{i32 2, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"wchar_size", i32 4}
+!10 = !{!"clang version 10.0.0"}
+!11 = distinct !DISubprogram(name: "foo", scope: !3, file: !3, line: 8, type: !12, scopeLine: 9, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !4)
+!12 = !DISubroutineType(types: !13)
+!13 = !{!14, !14}
+!14 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "bees", file: !3, line: 1, size: 64, elements: !15)
+!15 = !{!16, !17}
+!16 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !14, file: !3, line: 2, baseType: !6, size: 32)
+!17 = !DIDerivedType(tag: DW_TAG_member, name: "b", scope: !14, file: !3, line: 3, baseType: !6, size: 32, offset: 32)
+!18 = !DILocalVariable(name: "bumble", arg: 1, scope: !11, file: !3, line: 8, type: !14)
+!19 = !DILocation(line: 0, scope: !11)
+!20 = !DILocation(line: 10, column: 10, scope: !11)
+!21 = !DILocalVariable(name: "temp", scope: !11, file: !3, line: 11, type: !6)
+!22 = !DILocation(line: 12, column: 3, scope: !11)