[llvm] c6286b3 - [llvm][DebugInfo] Support DW_AT_linkage_names that are different between declaration and definition (#154137)

[via llvm-commits]

Author: Michael Buch
Date: 2025-09-01T15:24:06+01:00
New Revision: c6286b30bd6eaa55a53891bde77a5e82879d01f0

URL: https://github.com/llvm/llvm-project/commit/c6286b30bd6eaa55a53891bde77a5e82879d01f0
DIFF: https://github.com/llvm/llvm-project/commit/c6286b30bd6eaa55a53891bde77a5e82879d01f0.diff

LOG: [llvm][DebugInfo] Support DW_AT_linkage_names that are different between declaration and definition (#154137)

This patch is motivated by
https://github.com/llvm/llvm-project/pull/149827, where we plan on using
mangled names on structor declarations to find the exact structor
definition that LLDB's expression evaluator should call.

So far LLVM expects the declaration and definition linkage names to be
identical (or the declaration to just not have a linkage name). But we
plan on attaching the GCC-style "unified" mangled name to declarations,
which will be different to linkage name on the definition. This patch
relaxes this restriction.

Added: 
    llvm/test/DebugInfo/Generic/structor-declaration-linkage-names.ll

Modified: 
    llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index 477b66484c20c..d76fd0c010209 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -1410,11 +1410,8 @@ bool DwarfUnit::applySubprogramDefinitionAttributes(const DISubprogram *SP,
 
   // Add the linkage name if we have one and it isn't in the Decl.
   StringRef LinkageName = SP->getLinkageName();
-  assert(((LinkageName.empty() || DeclLinkageName.empty()) ||
-          LinkageName == DeclLinkageName) &&
-         "decl has a linkage name and it is 
diff erent");
-  if (DeclLinkageName.empty() &&
-      // Always emit it for abstract subprograms.
+  // Always emit linkage name for abstract subprograms.
+  if (DeclLinkageName != LinkageName &&
       (DD->useAllLinkageNames() || DU->getAbstractScopeDIEs().lookup(SP)))
     addLinkageName(SPDie, LinkageName);
 

diff  --git a/llvm/test/DebugInfo/Generic/structor-declaration-linkage-names.ll b/llvm/test/DebugInfo/Generic/structor-declaration-linkage-names.ll
new file mode 100644
index 0000000000000..9b1f2a5b2a186
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/structor-declaration-linkage-names.ll
@@ -0,0 +1,68 @@
+; RUN: %llc_dwarf < %s -filetype=obj | llvm-dwarfdump -debug-info - | FileCheck %s
+
+; Make sure we attach DW_AT_linkage_name on function declarations but only
+; attach it on definitions if the value is 
diff erent than on the declaration.
+
+target triple = "arm64-apple-macosx"
+
+define void @_Z11SameLinkagev() !dbg !4 {
+entry:
+  ret void
+}
+
+; CHECK:     DW_AT_linkage_name ("_Z11SameLinkagev")
+; CHECK:     DW_AT_declaration (true)
+; CHECK-NOT: DW_AT_linkage_name ("_Z11SameLinkagev")
+
+define void @_Z11DiffLinkagev() !dbg !8 {
+entry:
+  ret void
+}
+
+; CHECK: DW_AT_linkage_name ("SomeName")
+; CHECK: DW_AT_declaration (true)
+; CHECK: DW_AT_linkage_name ("_Z11DiffLinkagev")
+
+define void @_Z15EmptyDefLinkagev() !dbg !10 {
+entry:
+  ret void
+}
+
+; CHECK:     DW_AT_linkage_name ("_Z15EmptyDefLinkagev")
+; CHECK:     DW_AT_declaration (true)
+; CHECK-NOT: DW_AT_linkage_name
+
+define void @_Z16EmptyDeclLinkagev() !dbg !12 {
+entry:
+  ret void
+}
+
+; CHECK: DW_AT_declaration (true)
+; CHECK: DW_AT_linkage_name ("_Z16EmptyDeclLinkagev")
+
+define void @_Z13EmptyLinkagesv() !dbg !14 {
+entry:
+  ret void
+}
+
+; CHECK-NOT: DW_AT_linkage_name
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: Apple, sysroot: "/")
+!1 = !DIFile(filename: "foo.cpp", directory: "/tmp")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = distinct !DISubprogram(name: "SameLinkage", linkageName: "_Z11SameLinkagev", scope: !1, file: !1, line: 3, type: !5, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, declaration: !7)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null}
+!7 = !DISubprogram(name: "SameLinkage", linkageName: "_Z11SameLinkagev", scope: !1, file: !1, line: 3, type: !5, scopeLine: 3, flags: DIFlagPrototyped, spFlags: 0)
+!8 = distinct !DISubprogram(name: "DiffLinkage", linkageName: "_Z11DiffLinkagev", scope: !1, file: !1, line: 5, type: !5, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, declaration: !9)
+!9 = !DISubprogram(name: "DiffLinkage", linkageName: "SomeName", scope: !1, file: !1, line: 3, type: !5, scopeLine: 3, flags: DIFlagPrototyped, spFlags: 0)
+!10 = distinct !DISubprogram(name: "EmptyDefLinkage", linkageName: "", scope: !1, file: !1, line: 5, type: !5, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, declaration: !11)
+!11 = !DISubprogram(name: "EmptyDefLinkage", linkageName: "_Z15EmptyDefLinkagev", scope: !1, file: !1, line: 3, type: !5, scopeLine: 3, flags: DIFlagPrototyped, spFlags: 0)
+!12 = distinct !DISubprogram(name: "EmptyDeclLinkage", linkageName: "_Z16EmptyDeclLinkagev", scope: !1, file: !1, line: 5, type: !5, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, declaration: !13)
+!13 = !DISubprogram(name: "EmptyDeclLinkage", linkageName: "", scope: !1, file: !1, line: 3, type: !5, scopeLine: 3, flags: DIFlagPrototyped, spFlags: 0)
+!14 = distinct !DISubprogram(name: "EmptyLinkages", linkageName: "", scope: !1, file: !1, line: 5, type: !5, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, declaration: !15)
+!15 = !DISubprogram(name: "EmptyLinkages", linkageName: "", scope: !1, file: !1, line: 3, type: !5, scopeLine: 3, flags: DIFlagPrototyped, spFlags: 0)