From 9c2463622dd58b6b3987fe80509c22f5df02b88c Mon Sep 17 00:00:00 2001
From: Hsiangkai Wang <hsiangkai@gmail.com>
Date: Tue, 25 Sep 2018 06:09:50 +0000
Subject: [PATCH] [DebugInfo] Do not generate address info for removed debug
 labels.

In some senario, LLVM will remove llvm.dbg.labels in IR. For example,
when the labels are in unreachable blocks, these labels will not
be generated in LLVM IR. In the case, these debug labels will have
address zero as their address. It is not legal address for debugger to
set breakpoints or query sources. So, the patch inhibits the address info
(DW_AT_low_pc) of removed labels.

Differential Revision: https://reviews.llvm.org/D51908

llvm-svn: 342943
---
 llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp   |  7 ++--
 .../DebugInfo/Generic/debug-label-unreached.ll     | 39 ++++++++++++++++++++++
 2 files changed, 42 insertions(+), 4 deletions(-)
 create mode 100644 llvm/test/DebugInfo/Generic/debug-label-unreached.ll

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index ee68219..496c80a 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -865,10 +865,9 @@ void DwarfCompileUnit::finishEntityDefinition(const DbgEntity *Entity) {
       llvm_unreachable("DbgEntity must be DbgVariable or DbgLabel.");
   }
 
-  if (Label) {
-    const MCSymbol *Sym = Label->getSymbol();
-    addLabelAddress(*Die, dwarf::DW_AT_low_pc, Sym);
-  }
+  if (Label)
+    if (const auto *Sym = Label->getSymbol())
+      addLabelAddress(*Die, dwarf::DW_AT_low_pc, Sym);
 }
 
 DbgEntity *DwarfCompileUnit::getExistingAbstractEntity(const DINode *Node) {
diff --git a/llvm/test/DebugInfo/Generic/debug-label-unreached.ll b/llvm/test/DebugInfo/Generic/debug-label-unreached.ll
new file mode 100644
index 0000000..3c56fe7
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/debug-label-unreached.ll
@@ -0,0 +1,39 @@
+; Test unreachable llvm.dbg.label
+;
+; RUN: llc -filetype=obj -split-dwarf-file debug.dwo -o - %s | llvm-dwarfdump -v - | FileCheck %s
+;
+; CHECK: .debug_info.dwo contents:
+; CHECK: DW_TAG_label
+; CHECK-NEXT: DW_AT_name {{.*}}"done"
+; CHECK-NOT: {{DW_TAG|NULL}}
+; CHECK: DW_AT_low_pc
+; CHECK: DW_TAG_label
+; CHECK-NEXT: DW_AT_name {{.*}}"removed"
+; CHECK-NOT: DW_AT_low_pc
+source_filename = "debug-label-unreached.c"
+
+define dso_local i32 @foo(i32 %a, i32 %b) !dbg !8 {
+entry:
+  %sum = add nsw i32 %a, %b, !dbg !12
+  call void @llvm.dbg.label(metadata !11), !dbg !12
+  ret i32 %sum, !dbg !13
+}
+
+declare void @llvm.dbg.label(metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: true, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "debug-label-unreached.c", directory: "./")
+!2 = !{}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7}
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 8, type: !5, isLocal: false, isDefinition: true, scopeLine: 9, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !9)
+!9 = !{!10, !11}
+!10 = !DILabel(scope: !8, name: "removed", file: !1, line: 11)
+!11 = !DILabel(scope: !8, name: "done", file: !1, line: 13)
+!12 = !DILocation(line: 13, column: 1, scope: !8)
+!13 = !DILocation(line: 14, column: 5, scope: !8)
-- 
2.7.4