[Debuginfo] Prevent CodeGenPrepare from dropping debuginfo references.

This fixes PR39845. CodeGenPrepare employs a transactional model when 
performing optimizations, i.e. it changes the IR to attempt an optimization
and rolls back the change when it finds the change inadequate. It is during
the rollback that references to locals were dropped from debug value 
intrinsics. This patch reinstates debuginfo references during rollbacks.

Reviewers: aprantl, vsk

Differential Revision: https://reviews.llvm.org/D55396 

llvm-svn: 348896

1 files changed, 75 insertions, 0 deletions

diff --git a/llvm/test/DebugInfo/Generic/codegenprep-value.ll b/llvm/test/DebugInfo/Generic/codegenprep-value.ll
new file mode 100644
index 00000000000..cf394383b10
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/codegenprep-value.ll
@@ -0,0 +1,75 @@
+; RUN: opt -codegenprepare -S %s | FileCheck %s
+;
+; Generated from the following source with:
+; clang -O2 -g -S -emit-llvm -mllvm -stop-after=indirectbr-expand test.cpp
+;
+; extern void use(int);
+; extern int foo(long long);
+; 
+; void test(int p)
+; {
+;   int i = p + 4;
+;   (void)foo(i);  // sign extension of i
+;   if (p)
+;     return;
+;   use(i);        // use of original i
+; }
+;
+; PR39845: Check that CodeGenPrepare does not drop the reference to a local when it is
+;          sign-extended and used later.
+;
+; CHECK: define{{.*}}test
+; CHECK: call{{.*}}dbg.value(metadata i32 %p
+; CHECK: call{{.*}}dbg.value(metadata i32 %add
+;
+define dso_local void @_Z4testi(i32 %p) local_unnamed_addr !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata i32 %p, metadata !12, metadata !DIExpression()), !dbg !14
+  %add = add nsw i32 %p, 4, !dbg !15
+  call void @llvm.dbg.value(metadata i32 %add, metadata !13, metadata !DIExpression()), !dbg !16
+  %conv = sext i32 %add to i64, !dbg !17
+  %call = tail call i32 @_Z3foox(i64 %conv), !dbg !18
+  %tobool = icmp eq i32 %p, 0, !dbg !19
+  br i1 %tobool, label %if.end, label %cleanup, !dbg !21
+
+if.end:
+  tail call void @_Z3usei(i32 %add), !dbg !22
+  br label %cleanup, !dbg !23
+
+cleanup:
+  ret void, !dbg !23
+}
+
+declare dso_local i32 @_Z3foox(i64) local_unnamed_addr
+declare dso_local void @_Z3usei(i32) local_unnamed_addr
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 8.0.0 (trunk 348209)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/home/test/src")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 8.0.0 (trunk 348209)"}
+!7 = distinct !DISubprogram(name: "test", linkageName: "_Z4testi", scope: !1, file: !1, line: 4, type: !8, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12, !13}
+!12 = !DILocalVariable(name: "p", arg: 1, scope: !7, file: !1, line: 4, type: !10)
+!13 = !DILocalVariable(name: "i", scope: !7, file: !1, line: 6, type: !10)
+!14 = !DILocation(line: 4, column: 15, scope: !7)
+!15 = !DILocation(line: 6, column: 13, scope: !7)
+!16 = !DILocation(line: 6, column: 7, scope: !7)
+!17 = !DILocation(line: 7, column: 13, scope: !7)
+!18 = !DILocation(line: 7, column: 9, scope: !7)
+!19 = !DILocation(line: 8, column: 7, scope: !20)
+!20 = distinct !DILexicalBlock(scope: !7, file: !1, line: 8, column: 7)
+!21 = !DILocation(line: 8, column: 7, scope: !7)
+!22 = !DILocation(line: 10, column: 3, scope: !7)
+!23 = !DILocation(line: 11, column: 1, scope: !7)