[DebugInfo] Construct nested types on behalf of owner CU

[evgeny777]

Summary

This was originally suggested in D58538

[dblaikie]

Would it be possible/practical/reasonable to split getOrCreateTypeDIE at 643, before the createAndAddDIE? And at that point do the switch to the appropriate CU (basically as soon as we get the context DIE and can determine which unit is the appropriate one to build the type DIE in)

[evgeny777]

Would it be possible/practical/reasonable to split getOrCreateTypeDIE

I think so, but I thought it's easier to do things this way, because AFAIK:

• DIBaseType and DISubroutineType can't introduce the problem because they're either bound to variable or typedef (DIDerivedType)
• Using type units also isn't problematic because in such case DINodes are not shareable across CUs

Ok, I'll try splitting and see how it goes

[evgeny777]

Split getOrCreateTypeDIE

[dblaikie]

Looks great - thanks!

lib/CodeGen/AsmPrinter/DwarfUnit.cpp

else if (auto *STy = dyn_cast<DISubroutineType>(Ty))
     constructTypeDIE(TyDIE, STy);
   else if (auto *CTy = dyn_cast<DICompositeType>(Ty)) {
     if (DD->generateTypeUnits() && !Ty->isForwardDecl())
       if (MDString *TypeId = CTy->getRawIdentifier()) {
         DD->addDwarfTypeUnitType(getCU(), TypeId->getString(), TyDIE, CTy);
         // Skip updating the accelerator tables since this is not the full type.
         return &TyDIE;
       }
-    constructTypeDIE(TyDIE, CTy);
+    static_cast<DwarfUnit *>(TyDIE.getUnit())->constructTypeDIE(TyDIE, CTy);
   } else {
-    constructTypeDIE(TyDIE, cast<DIDerivedType>(Ty));
+    static_cast<DwarfUnit *>(TyDIE.getUnit())
+        ->constructTypeDIE(TyDIE, cast<DIDerivedType>(Ty));
   }
 
   return &TyDIE;
 }
 
 void DwarfUnit::updateAcceleratorTables(const DIScope *Context,
                                         const DIType *Ty, const DIE &TyDIE) {
   if (!Ty->getName().empty() && !Ty->isForwardDecl()) {

test/DebugInfo/X86/nested_types.ll

+; Check that debug info for nested types is generated correctly.
+; With full LTO we may end up in several compilation units sharing
+; single object file. In such case it's possible that nested type DIE
+; is created on behalf of CU#1 and parent type DIE is created on 
+; behalf of CU#2. In such case we may end up with broken source line
+; attributes, because file ids don't coincide in CU#1 and CU#2
+
+; Sources used to generate this sample (C++)
+; // File: inc1.h
+; struct S {
+;   struct Nested {};
+;   typedef int NestedTypedef;
+; };
+;
+; // File inc2.h
+; extern int x;
+; int x;
+; 
+; // File foo.cpp
+; #include "inc1.h"
+; S s;
+;
+; // File bar.cpp
+; #include "inc1.h"
+; #include "inc2.h"
+; void f3() {
+;   S::Nested n;
+;   S::NestedTypedef n2;
+; }
+
+; RUN: llc -filetype=obj %s -o %t
+; RUN: llvm-dwarfdump %t | FileCheck %s
+
+; CHECK:             DW_AT_name ("Nested")
+; CHECK-NEXT:        DW_AT_byte_size (0x01)
+; CHECK-NEXT:        DW_AT_decl_file ("{{.*}}inc1.h")
+; CHECK-NEXT:        DW_AT_decl_line (2)
+
+; CHECK:             DW_AT_name ("NestedTypedef")
+; CHECK-NEXT:        DW_AT_decl_file ("{{.*}}inc1.h")
+; CHECK-NEXT:        DW_AT_decl_line (3)
+
+source_filename = "llvm-link"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.S = type { i8 }
+
+@s = dso_local global %struct.S zeroinitializer, align 1, !dbg !0
+@x = dso_local global i32 0, align 4, !dbg !8
+
+; Function Attrs: noinline nounwind optnone uwtable
+define dso_local void @_Z2f3v() !dbg !19 {
+entry:
+  %n = alloca %struct.S, align 1
+  %n2 = alloca i32, align 4
+  call void @llvm.dbg.declare(metadata %struct.S* %n, metadata !22, metadata !DIExpression()), !dbg !24
+  call void @llvm.dbg.declare(metadata i32* %n2, metadata !25, metadata !DIExpression()), !dbg !27
+  ret void, !dbg !28
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!2, !10}
+!llvm.ident = !{!15, !15}
+!llvm.module.flags = !{!16, !17, !18}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "s", scope: !2, file: !3, line: 2, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 9.0.0 (trunk 354767)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None)
+!3 = !DIFile(filename: "foo.cpp", directory: "/home/evgeny/work/cpp_lexer/sample3")
+!4 = !{}
+!5 = !{!0}
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !7, line: 1, size: 8, flags: DIFlagTypePassByValue | DIFlagTrivial, elements: !4, identifier: "_ZTS1S")
+!7 = !DIFile(filename: "./inc1.h", directory: "/home/evgeny/work/cpp_lexer/sample3")
+!8 = !DIGlobalVariableExpression(var: !9, expr: !DIExpression())
+!9 = distinct !DIGlobalVariable(name: "x", scope: !10, file: !13, line: 2, type: !14, isLocal: false, isDefinition: true)
+!10 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !11, producer: "clang version 9.0.0 (trunk 354767)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !12, nameTableKind: None)
+!11 = !DIFile(filename: "bar.cpp", directory: "/home/evgeny/work/cpp_lexer/sample3")
+!12 = !{!8}
+!13 = !DIFile(filename: "./inc2.h", directory: "/home/evgeny/work/cpp_lexer/sample3")
+!14 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!15 = !{!"clang version 9.0.0 (trunk 354767)"}
+!16 = !{i32 2, !"Dwarf Version", i32 4}
+!17 = !{i32 2, !"Debug Info Version", i32 3}
+!18 = !{i32 1, !"wchar_size", i32 4}
+!19 = distinct !DISubprogram(name: "f3", linkageName: "_Z2f3v", scope: !11, file: !11, line: 3, type: !20, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !10, retainedNodes: !4)
+!20 = !DISubroutineType(types: !21)
+!21 = !{null}
+!22 = !DILocalVariable(name: "n", scope: !19, file: !11, line: 4, type: !23)
+!23 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Nested", scope: !6, file: !7, line: 2, size: 8, flags: DIFlagTypePassByValue | DIFlagTrivial, elements: !4, identifier: "_ZTSN1S6NestedE")
+!24 = !DILocation(line: 4, column: 13, scope: !19)
+!25 = !DILocalVariable(name: "n2", scope: !19, file: !11, line: 5, type: !26)
+!26 = !DIDerivedType(tag: DW_TAG_typedef, name: "NestedTypedef", scope: !6, file: !7, line: 3, baseType: !14)
+!27 = !DILocation(line: 5, column: 20, scope: !19)
+!28 = !DILocation(line: 6, column: 1, scope: !19)
+