[llvm] r342943 - [DebugInfo] Do not generate address info for removed debug labels.

[Justin Bogner via llvm-commits]

The test that this adds is crashing on the macOS bots:

  http://green.lab.llvm.org/green/job/clang-stage1-cmake-RA-incremental/53550/

I've gone ahead and reverted the commit for now in r342993. Let me know
if you need any help investigating this.

Hsiangkai Wang via llvm-commits <llvm-commits at lists.llvm.org> writes:
> Author: hsiangkai
> Date: Mon Sep 24 23:09:50 2018
> New Revision: 342943
>
> URL: http://llvm.org/viewvc/llvm-project?rev=342943&view=rev
> Log:
> [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
>
> Added:
>     llvm/trunk/test/DebugInfo/Generic/debug-label-unreached.ll
> Modified:
>     llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp?rev=342943&r1=342942&r2=342943&view=diff
> ==============================================================================
>
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp Mon Sep 24 23:09:50 2018
> @@ -865,10 +865,9 @@ void DwarfCompileUnit::finishEntityDefin
>        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) {
>
> Added: llvm/trunk/test/DebugInfo/Generic/debug-label-unreached.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/Generic/debug-label-unreached.ll?rev=342943&view=auto
> ==============================================================================
> --- llvm/trunk/test/DebugInfo/Generic/debug-label-unreached.ll (added)
> +++ llvm/trunk/test/DebugInfo/Generic/debug-label-unreached.ll Mon Sep 24 23:09:50 2018
> @@ -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)
>
>
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