[DWARF] Put linkage-name on abstract origin even when there's a declaration

[probinson]

Summary

In r266692, we made it possible to emit linkage-names only for inlined subroutines, putting the attribute
on the abstract origin DIE (which counts as the definition DIE). However, this fails when we emit a
declaration DIE prior to the definition DIE, because (a) when we process the declaration, we don't emit
the linkage name, because it's not an abstract origin; and (b) when we process the definition, we look at
the declaration metadata and see it has a linkage name, so we think it has already been emitted.

Look at the actual DIE, rather than the metadata, to see whether we've already emitted the linkage name.

[aprantl]

test/DebugInfo/Generic/linkage-name-abstract.ll

118 ↗

(On Diff #79977)

We typically strip out all non-essential attributes.

[dblaikie]

If possible it'd be nice to avoid having to search through the DIE's attributes to make this determination - any way we can make the right determination more directly/without that information channel?

[probinson]

lib/CodeGen/AsmPrinter/DwarfUnit.cpp

1162 ↗

(On Diff #79977)

I had thought about making this

if (DD->useAllLinkageNames())
  DeclLinkageName = SPDecl->getLinkageName();

and so not needing the extra static function, but actually looking into the DIE itself seemed more robust.

[probinson]

In D27320#611044, @dblaikie wrote:

If possible it'd be nice to avoid having to search through the DIE's attributes to make this determination - any way we can make the right determination more directly/without that information channel?

See the inline comment. It's depending on the way the condition works for actually emitting the linkage name, but as it's all inside the same method I suppose it's okay.

[probinson]

Simpler cheaper check. Remove noisy attributes from test.

[dblaikie]

Ah, I get it - sorry.

A comment's probably a good idea.

Also - if you make the member function static it might simplify the test case a fair bit.

[probinson]

In D27320#611096, @dblaikie wrote:

Ah, I get it - sorry.

A comment's probably a good idea.

Also - if you make the member function static it might simplify the test case a fair bit.

Added a comment. Making the member function static did tighten up the IR and metadata a bit.
Thanks!

llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

bool DwarfUnit::applySubprogramDefinitionAttributes(const DISubprogram *SP,
                                                     DIE &SPDie) {
   DIE *DeclDie = nullptr;
   StringRef DeclLinkageName;
   if (auto *SPDecl = SP->getDeclaration()) {
     DeclDie = getDIE(SPDecl);
     assert(DeclDie && "This DIE should've already been constructed when the "
                       "definition DIE was created in "
                       "getOrCreateSubprogramDIE");
+    // Look at the Decl's linkage name only if we emitted it.
+    if (DD->useAllLinkageNames())
       DeclLinkageName = SPDecl->getLinkageName();
     unsigned DeclID =
         getOrCreateSourceID(SPDecl->getFilename(), SPDecl->getDirectory());
     unsigned DefID = getOrCreateSourceID(SP->getFilename(), SP->getDirectory());
     if (DeclID != DefID)
       addUInt(SPDie, dwarf::DW_AT_decl_file, None, DefID);
 
     if (SP->getLine() != SPDecl->getLine())
       addUInt(SPDie, dwarf::DW_AT_decl_line, None, SP->getLine());

llvm/trunk/test/DebugInfo/Generic/linkage-name-abstract.ll

 ; IR generated from clang -O0 with:
 ; void f1();
 ; __attribute__((always_inline)) void f2() { 
 ;   f1();
 ; }
 ; void f3() {
 ;   f2();
 ; }
+;
+; struct F4 {
+;   __attribute__((always_inline)) void f5();
+; };
+; void F4::f5() {
+;   f1();
+; }
+; void f6() {
+;   F4::f5();
+; }
 
-; Show that there's only one linkage_name.
-; ONENAME:     {{DW_AT(_MIPS)?_linkage_name}}
+; Show that the only linkage names are for the inlined functions,
+; because those are the ones with an abstract origin.
+; ONENAME-NOT: {{DW_AT(_MIPS)?_linkage_name}}
+; ONENAME:     {{DW_AT(_MIPS)?_linkage_name}} {{.*}} "_Z2f2v"
+; ONENAME-NOT: {{DW_AT(_MIPS)?_linkage_name}}
+; ONENAME:     {{DW_AT(_MIPS)?_linkage_name}} {{.*}} "_ZN2F42f5Ev"
 ; ONENAME-NOT: {{DW_AT(_MIPS)?_linkage_name}}
 
-; Locate the subprogram DIE with the linkage name.
-; Show that the inlined_subroutine refers to it.
-; REF:     DW_TAG_subprogram
-; REF:     [[FOO:0x.*]]: DW_TAG_subprogram
-; REF-NOT: {{DW_TAG|NULL}}
-; REF:     {{DW_AT(_MIPS)?_linkage_name}}
-; REF:     DW_TAG_inlined_subroutine
-; REF-NOT: {{DW_TAG|NULL}}
-; REF:     DW_AT_abstract_origin {{.*}} {[[FOO]]}
+; For f2() we see the definition pointing to an abstract origin DIE,
+; which in turn is where the linkage_name is; and then there's
+; an inlined_subroutine pointing back to the abstract origin.
+; The order of these DIEs is not important of course, just the links.
+; REF:      DW_TAG_subprogram
+; REF-NOT:  {{DW_TAG|NULL}}
+; REF:      DW_AT_abstract_origin {{.*}} {[[F2:0x.*]]} "_Z2f2v"
+; REF:      [[F2]]: DW_TAG_subprogram
+; REF-NEXT: linkage_name {{.*}} "_Z2f2v"
+; REF:      DW_TAG_inlined_subroutine
+; REF-NOT:  {{DW_TAG|NULL}}
+; REF:      DW_AT_abstract_origin {{.*}} {[[F2]]}
+
+; For F4::f5(), first we see the in-class declaration,
+; then the definition, abstract origin, and the inlined_subroutine.
+; REF:      DW_TAG_structure_type
+; REF-NEXT: DW_AT_name {{.*}} "F4"
+; REF-NOT:  {{DW_TAG|NULL}}
+; REF:      [[F5_DECL:0x.*]]: DW_TAG_subprogram
+; REF-NEXT: DW_AT_name {{.*}} "f5"
+; REF:      DW_TAG_subprogram
+; REF-NOT:  {{DW_TAG|NULL}}
+; REF:      DW_AT_abstract_origin {{.*}} {[[F5_ABS:0x.*]]} "_ZN2F42f5Ev"
+; REF:      [[F5_ABS]]: DW_TAG_subprogram
+; REF-NOT:  {{DW_TAG|NULL}}
+; REF:      linkage_name {{.*}} "_ZN2F42f5Ev"
+; REF-NEXT: DW_AT_specification {{.*}} {[[F5_DECL]]}
+; REF:      DW_TAG_inlined_subroutine
+; REF-NOT:  {{DW_TAG|NULL}}
+; REF:      DW_AT_abstract_origin {{.*}} {[[F5_ABS]]}
+
 
 ; Function Attrs: alwaysinline uwtable
-define void @_Z2f2v() #0 !dbg !4 {
+define void @_Z2f2v() #0 !dbg !6 {
 entry:
-  call void @_Z2f1v(), !dbg !11
-  ret void, !dbg !12
+  call void @_Z2f1v(), !dbg !9
+  ret void, !dbg !10
 }
 
 declare void @_Z2f1v()
 
 ; Function Attrs: uwtable
-define void @_Z2f3v() #2 !dbg !7 {
+define void @_Z2f3v() !dbg !11 {
+entry:
+  call void @_Z2f1v(), !dbg !12
+  ret void, !dbg !14
+}
+
+; Function Attrs: alwaysinline uwtable
+define void @_ZN2F42f5Ev() #0 align 2 !dbg !15 {
+entry:
+  call void @_Z2f1v(), !dbg !19
+  ret void, !dbg !20
+}
+
+; Function Attrs: uwtable
+define void @_Z2f6v() !dbg !21 {
 entry:
-  call void @_Z2f1v(), !dbg !13
-  ret void, !dbg !15
+  call void @_Z2f1v(), !dbg !22
+  ret void, !dbg !24
 }
 
-attributes #0 = { alwaysinline uwtable }
-attributes #2 = { uwtable }
+attributes #0 = { alwaysinline }
 
 !llvm.dbg.cu = !{!0}
-!llvm.module.flags = !{!8, !9}
-!llvm.ident = !{!10}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
 
-!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.9.0 (trunk 265282)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
-!1 = !DIFile(filename: "linkage-name-abstract.cpp", directory: "/home/probinson/projects/scratch")
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 4.0.0 (trunk 288231)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "linkage-name-abstract-static.cpp", directory: "/home/probinson/projects/scratch")
 !2 = !{}
-!4 = distinct !DISubprogram(name: "f2", linkageName: "_Z2f2v", scope: !1, file: !1, line: 2, type: !5, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
-!5 = !DISubroutineType(types: !6)
-!6 = !{null}
-!7 = distinct !DISubprogram(name: "f3", linkageName: "_Z2f3v", scope: !1, file: !1, line: 5, type: !5, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
-!8 = !{i32 2, !"Dwarf Version", i32 4}
-!9 = !{i32 2, !"Debug Info Version", i32 3}
-!10 = !{!"clang version 3.9.0 (trunk 265282)"}
-!11 = !DILocation(line: 3, column: 3, scope: !4)
-!12 = !DILocation(line: 4, column: 1, scope: !4)
-!13 = !DILocation(line: 3, column: 3, scope: !4, inlinedAt: !14)
-!14 = distinct !DILocation(line: 6, column: 3, scope: !7)
-!15 = !DILocation(line: 7, column: 1, scope: !7)
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 4.0.0 (trunk 288231)"}
+!6 = distinct !DISubprogram(name: "f2", linkageName: "_Z2f2v", scope: !1, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!7 = !DISubroutineType(types: !8)
+!8 = !{null}
+!9 = !DILocation(line: 3, column: 3, scope: !6)
+!10 = !DILocation(line: 4, column: 1, scope: !6)
+!11 = distinct !DISubprogram(name: "f3", linkageName: "_Z2f3v", scope: !1, file: !1, line: 5, type: !7, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!12 = !DILocation(line: 3, column: 3, scope: !6, inlinedAt: !13)
+!13 = distinct !DILocation(line: 6, column: 3, scope: !11)
+!14 = !DILocation(line: 7, column: 1, scope: !11)
+!15 = distinct !DISubprogram(name: "f5", linkageName: "_ZN2F42f5Ev", scope: !16, file: !1, line: 12, type: !7, isLocal: false, isDefinition: true, scopeLine: 12, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !18, variables: !2)
+!16 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "F4", file: !1, line: 9, size: 8, elements: !17, identifier: "_ZTS2F4")
+!17 = !{!18}
+!18 = !DISubprogram(name: "f5", linkageName: "_ZN2F42f5Ev", scope: !16, file: !1, line: 10, type: !7, isLocal: false, isDefinition: false, scopeLine: 10, flags: DIFlagPrototyped, isOptimized: false)
+!19 = !DILocation(line: 13, column: 3, scope: !15)
+!20 = !DILocation(line: 14, column: 1, scope: !15)
+!21 = distinct !DISubprogram(name: "f6", linkageName: "_Z2f6v", scope: !1, file: !1, line: 15, type: !7, isLocal: false, isDefinition: true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!22 = !DILocation(line: 13, column: 3, scope: !15, inlinedAt: !23)
+!23 = distinct !DILocation(line: 16, column: 3, scope: !21)
+!24 = !DILocation(line: 17, column: 1, scope: !21)