[DebugInfo] Recover debug intrinsics when killing duplicated/empty basic blocks

When basic blocks are killed, either due to being empty or to being an if.then
or if.else block whose complement contains identical instructions, some of the
debug intrinsics in that block are lost. This patch sinks those intrinsics
into the single successor block, setting them Undef if necessary to
prevent debug info from falling out-of-date.

Differential Revision: https://reviews.llvm.org/D70318

2 files changed, 138 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue-else.ll b/llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue-else.ll
new file mode 100644
index 00000000000..32962886be5
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue-else.ll
@@ -0,0 +1,67 @@
+; RUN: opt -simplifycfg -S < %s | FileCheck %s
+; Checks that when the if.then and if.else blocks are both eliminated by
+; SimplifyCFG, as the common code is hoisted out, the variables with a
+; dbg.value in either of those blocks are set undef just before the
+; conditional branch instruction.
+
+define i32 @"?fn@@YAHH@Z"(i32 %foo) !dbg !8 {
+; CHECK-LABEL: entry:
+entry:
+  call void @llvm.dbg.value(metadata i32 %foo, metadata !13, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 0, metadata !14, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 0, metadata !15, metadata !DIExpression()), !dbg !16
+  %cmp = icmp eq i32 %foo, 4, !dbg !17
+; CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata [[BEARDS:![0-9]+]]
+; CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata [[BIRDS:![0-9]+]]
+  br i1 %cmp, label %if.then, label %if.else, !dbg !17
+
+if.then:                                          ; preds = %entry
+  call void @llvm.dbg.value(metadata i32 8, metadata !14, metadata !DIExpression()), !dbg !16
+  br label %if.end, !dbg !18
+
+if.else:                                          ; preds = %entry
+  call void @llvm.dbg.value(metadata i32 4, metadata !14, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 8, metadata !15, metadata !DIExpression()), !dbg !16
+  br label %if.end, !dbg !21
+
+if.end:                                           ; preds = %if.else, %if.then
+  %beards.0 = phi i32 [ 8, %if.then ], [ 4, %if.else ], !dbg !23
+  call void @llvm.dbg.value(metadata i32 %beards.0, metadata !14, metadata !DIExpression()), !dbg !16
+  ret i32 %beards.0, !dbg !24
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+; CHECK-LABEL: }
+; CHECK: [[BEARDS]] = !DILocalVariable(name: "beards"
+; CHECK: [[BIRDS]] = !DILocalVariable(name: "birds"
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 10.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "C:\5Cdev\5Cllvm-project", checksumkind: CSK_MD5, checksum: "64604a72fdf5b6db8aa2328236bedd6b")
+!2 = !{}
+!3 = !{i32 2, !"CodeView", i32 1}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 2}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!7 = !{!"clang version 10.0.0 "}
+!8 = distinct !DISubprogram(name: "fn", linkageName: "?fn@@YAHH@Z", scope: !1, file: !1, line: 1, type: !9, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11, !11}
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !{!13, !14, !15}
+!13 = !DILocalVariable(name: "foo", arg: 1, scope: !8, file: !1, line: 1, type: !11)
+!14 = !DILocalVariable(name: "beards", scope: !8, file: !1, line: 2, type: !11)
+!15 = !DILocalVariable(name: "birds", scope: !8, file: !1, line: 3, type: !11)
+!16 = !DILocation(line: 0, scope: !8)
+!17 = !DILocation(line: 5, scope: !8)
+!18 = !DILocation(line: 8, scope: !19)
+!19 = distinct !DILexicalBlock(scope: !20, file: !1, line: 5)
+!20 = distinct !DILexicalBlock(scope: !8, file: !1, line: 5)
+!21 = !DILocation(line: 11, scope: !22)
+!22 = distinct !DILexicalBlock(scope: !20, file: !1, line: 8)
+!23 = !DILocation(line: 0, scope: !20)
+!24 = !DILocation(line: 13, scope: !8)
diff --git a/llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue-empty.ll b/llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue-empty.ll
new file mode 100644
index 00000000000..7d5e32a2d65
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue-empty.ll
@@ -0,0 +1,71 @@
+; RUN: opt -simplifycfg -S < %s | FileCheck %s
+; Checks that when the if.then block is eliminated due to containing no
+; instructions, the debug intrinsics are hoisted out of the block before its
+; deletion. The hoisted intrinsics should have undef values as the branch
+; behaviour is unknown to the intrinsics after hoisting.
+
+define dso_local i32 @"?fn@@YAHH@Z"(i32 %foo) local_unnamed_addr !dbg !8 {
+entry:
+  call void @llvm.dbg.value(metadata i32 %foo, metadata !13, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 0, metadata !14, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 0, metadata !15, metadata !DIExpression()), !dbg !16
+  %cmp = icmp eq i32 %foo, 4, !dbg !17
+  br i1 %cmp, label %if.then, label %if.else, !dbg !17
+
+if.then:                                          ; preds = %entry
+  call void @llvm.dbg.value(metadata i32 8, metadata !14, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 3, metadata !15, metadata !DIExpression()), !dbg !16
+  br label %if.end, !dbg !18
+
+if.else:                                          ; preds = %entry
+  call void @"?side@@YAXXZ"(), !dbg !21
+  call void @llvm.dbg.value(metadata i32 4, metadata !14, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 6, metadata !15, metadata !DIExpression()), !dbg !16
+  br label %if.end, !dbg !23
+
+; CHECK-LABEL: if.end:
+if.end:                                           ; preds = %if.else, %if.then
+; CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata [[BEARDS:![0-9]+]]
+; CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata [[BIRDS:![0-9]+]]
+  %beards.0 = phi i32 [ 8, %if.then ], [ 4, %if.else ], !dbg !24
+  call void @llvm.dbg.value(metadata i32 %beards.0, metadata !14, metadata !DIExpression()), !dbg !16
+  ret i32 %beards.0, !dbg !25
+}
+
+declare dso_local void @"?side@@YAXXZ"() local_unnamed_addr
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+; CHECK: [[BEARDS]] = !DILocalVariable(name: "beards"
+; CHECK: [[BIRDS]] = !DILocalVariable(name: "birds"
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 10.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "test2.cpp", directory: "C:\5Cdev\5Cllvm-project", checksumkind: CSK_MD5, checksum: "8ac5d40fcc9914d6479c1a770dfdc176")
+!2 = !{}
+!3 = !{i32 2, !"CodeView", i32 1}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 2}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!7 = !{!"clang version 10.0.0 "}
+!8 = distinct !DISubprogram(name: "fn", linkageName: "?fn@@YAHH@Z", scope: !1, file: !1, line: 3, type: !9, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11, !11}
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !{!13, !14, !15}
+!13 = !DILocalVariable(name: "foo", arg: 1, scope: !8, file: !1, line: 3, type: !11)
+!14 = !DILocalVariable(name: "beards", scope: !8, file: !1, line: 4, type: !11)
+!15 = !DILocalVariable(name: "birds", scope: !8, file: !1, line: 5, type: !11)
+!16 = !DILocation(line: 0, scope: !8)
+!17 = !DILocation(line: 7, scope: !8)
+!18 = !DILocation(line: 10, scope: !19)
+!19 = distinct !DILexicalBlock(scope: !20, file: !1, line: 7)
+!20 = distinct !DILexicalBlock(scope: !8, file: !1, line: 7)
+!21 = !DILocation(line: 11, scope: !22)
+!22 = distinct !DILexicalBlock(scope: !20, file: !1, line: 10)
+!23 = !DILocation(line: 14, scope: !22)
+!24 = !DILocation(line: 0, scope: !20)
+!25 = !DILocation(line: 16, scope: !8)