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This patch is motivated by #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.

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llvmbot commented Aug 18, 2025

@llvm/pr-subscribers-debuginfo

Author: Michael Buch (Michael137)

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This patch is motivated by #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.


Full diff: https://github.com/llvm/llvm-project/pull/154137.diff

2 Files Affected:

  • (modified) llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp (+2-5)
  • (added) llvm/test/DebugInfo/Generic/structor-declaration-linkage-names.ll (+68)
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index b03fac2d22a52..4904ad03199c7 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -1403,11 +1403,8 @@ 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 different");
-  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 different 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)

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That looks good!

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