ADCE: Remove debug info intrinsics in dead scopes

During ADCE, track which debug info scopes still have live references
from the code, and delete debug info intrinsics for the dead ones.

These intrinsics describe the locations of variables (in registers or
stack slots).  If there's no code left corresponding to a variable's
scope, then there's no way to reference the variable in the debugger and
it doesn't matter what its value is.

I add a DEBUG printout when the described location in an SSA register,
in case it helps some trying to track down why locations get lost.
However, we still delete these; the scope itself isn't attached to any
real code, so the ship has already sailed.

llvm-svn: 264800

1 files changed, 101 insertions, 0 deletions

diff --git a/llvm/test/Transforms/ADCE/debug-info-intrinsic.ll b/llvm/test/Transforms/ADCE/debug-info-intrinsic.ll
new file mode 100644
index 00000000000..fc8011bd87a
--- /dev/null
+++ b/llvm/test/Transforms/ADCE/debug-info-intrinsic.ll
@@ -0,0 +1,101 @@
+; RUN: opt -adce -S < %s | FileCheck %s
+; Test that debug info intrinsics in dead scopes get eliminated by -adce.
+
+; Generated with 'clang -g -S -emit-llvm | opt -mem2reg -inline' at r262899
+; (before -adce was augmented) and then hand-reduced.  This was the input:
+;
+;;void sink(void);
+;;
+;;void variable_in_unused_subscope(void) {
+;;  { int i = 0; }
+;;  sink();
+;;}
+;;
+;;void variable_in_parent_scope(void) {
+;;  int i = 0;
+;;  { sink(); }
+;;}
+;;
+;;static int empty_function_with_unused_variable(void) {
+;;  { int i = 0; }
+;;  return 0;
+;;}
+;;
+;;void calls_empty_function_with_unused_variable_in_unused_subscope(void) {
+;;  { empty_function_with_unused_variable(); }
+;;  sink();
+;;}
+
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+declare void @sink()
+
+; CHECK-LABEL: define void @variable_in_unused_subscope(
+define void @variable_in_unused_subscope() !dbg !4 {
+; CHECK-NEXT: entry:
+; CHECK-NEXT:   call void @sink
+; CHECK-NEXT:   ret void
+entry:
+  call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !15, metadata !17), !dbg !18
+  call void @sink(), !dbg !19
+  ret void, !dbg !20
+}
+
+; CHECK-LABEL: define void @variable_in_parent_scope(
+define void @variable_in_parent_scope() !dbg !7 {
+; CHECK-NEXT: entry:
+; CHECK-NEXT:   call void @llvm.dbg.value
+; CHECK-NEXT:   call void @sink
+; CHECK-NEXT:   ret void
+entry:
+  call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !21, metadata !17), !dbg !22
+  call void @sink(), !dbg !23
+  ret void, !dbg !25
+}
+
+; CHECK-LABEL: define void @calls_empty_function_with_unused_variable_in_unused_subscope(
+define void @calls_empty_function_with_unused_variable_in_unused_subscope() !dbg !8 {
+; CHECK-NEXT: entry:
+; CHECK-NEXT:   call void @sink
+; CHECK-NEXT:   ret void
+entry:
+  call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !26, metadata !17), !dbg !28
+  call void @sink(), !dbg !31
+  ret void, !dbg !32
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!14}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: 1, enums: !2, subprograms: !3)
+!1 = !DIFile(filename: "t.c", directory: "/path/to/test/Transforms/ADCE")
+!2 = !{}
+!3 = !{!4, !7, !8, !10}
+!4 = distinct !DISubprogram(name: "variable_in_unused_subscope", scope: !1, file: !1, line: 3, type: !5, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: false, variables: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null}
+!7 = distinct !DISubprogram(name: "variable_in_parent_scope", scope: !1, file: !1, line: 8, type: !5, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false, variables: !2)
+!8 = distinct !DISubprogram(name: "calls_empty_function_with_unused_variable_in_unused_subscope", scope: !1, file: !1, line: 18, type: !5, isLocal: false, isDefinition: true, scopeLine: 18, flags: DIFlagPrototyped, isOptimized: false, variables: !2)
+!10 = distinct !DISubprogram(name: "empty_function_with_unused_variable", scope: !1, file: !1, line: 13, type: !11, isLocal: true, isDefinition: true, scopeLine: 13, flags: DIFlagPrototyped, isOptimized: false, variables: !2)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13}
+!13 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!14 = !{i32 2, !"Debug Info Version", i32 3}
+!15 = !DILocalVariable(name: "i", scope: !16, file: !1, line: 4, type: !13)
+!16 = distinct !DILexicalBlock(scope: !4, file: !1, line: 4, column: 3)
+!17 = !DIExpression()
+!18 = !DILocation(line: 4, column: 9, scope: !16)
+!19 = !DILocation(line: 5, column: 3, scope: !4)
+!20 = !DILocation(line: 6, column: 1, scope: !4)
+!21 = !DILocalVariable(name: "i", scope: !7, file: !1, line: 9, type: !13)
+!22 = !DILocation(line: 9, column: 7, scope: !7)
+!23 = !DILocation(line: 10, column: 5, scope: !24)
+!24 = distinct !DILexicalBlock(scope: !7, file: !1, line: 10, column: 3)
+!25 = !DILocation(line: 11, column: 1, scope: !7)
+!26 = !DILocalVariable(name: "i", scope: !27, file: !1, line: 14, type: !13)
+!27 = distinct !DILexicalBlock(scope: !10, file: !1, line: 14, column: 3)
+!28 = !DILocation(line: 14, column: 9, scope: !27, inlinedAt: !29)
+!29 = distinct !DILocation(line: 19, column: 5, scope: !30)
+!30 = distinct !DILexicalBlock(scope: !8, file: !1, line: 19, column: 3)
+!31 = !DILocation(line: 20, column: 3, scope: !8)
+!32 = !DILocation(line: 21, column: 1, scope: !8)