[DWARF5][DebugInfo]: Added support for DebugInfo generation for auto return type for C++ member functions.

Summary:
This patch will provide support for auto return type for the C++ member
functions. Before this return type of the member function is deduced and
stored in the DIE.
This patch includes llvm side implementation of this feature.

Patch by: Awanish Pandey <[email protected]>

Reviewers: dblaikie, aprantl, shafik, alok, SouraVX, jini.susan.george

Reviewed by: dblaikie

Differential Revision: https://reviews.llvm.org/D70524

Author: Awanish Pandey

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -1165,6 +1165,14 @@ bool DwarfUnit::applySubprogramDefinitionAttributes(const DISubprogram *SP,
   DIE *DeclDie = nullptr;
   StringRef DeclLinkageName;
   if (auto *SPDecl = SP->getDeclaration()) {
+    DITypeRefArray DeclArgs, DefinationArgs;
+    DeclArgs = SPDecl->getType()->getTypeArray();
+    DefinationArgs = SP->getType()->getTypeArray();
+
+    if (DeclArgs.size() && DefinationArgs.size())
+      if (DeclArgs[0] != DefinationArgs[0])
+        addType(SPDie, DefinationArgs[0]);
+
     DeclDie = getDIE(SPDecl);
     assert(DeclDie && "This DIE should've already been constructed when the "
                       "definition DIE was created in "

llvm/test/DebugInfo/X86/debug-info-auto-return.ll

@@ -0,0 +1,70 @@
+; RUN: llc %s -filetype=obj -o - | llvm-dwarfdump -v - | FileCheck %s
+
+; CHECK: .debug_info contents:
+
+; CHECK: DW_TAG_subprogram 
+; CHECK-NEXT: DW_AT_linkage_name [DW_FORM_strx1]    (indexed {{.*}} string = "_ZN7myClass7findMaxEv")
+; CHECK: DW_AT_type [DW_FORM_ref4]     (cu + {{.*}} "auto")
+; CHECK-NEXT: DW_AT_declaration [DW_FORM_flag_present]      (true)
+
+; CHECK: DW_TAG_subprogram 
+; CHECK: DW_AT_type [DW_FORM_ref4]       (cu + {{.*}} "double")
+; CHECK: DW_AT_specification [DW_FORM_ref4]      (cu + {{.*}} "_ZN7myClass7findMaxEv")
+
+; C++ source to regenerate:
+; struct myClass {
+;    auto findMax();
+; };
+;
+; auto myClass::findMax() {
+;    return 0.0;
+; }
+
+; $ clang++ -O0 -g -gdwarf-5 debug-info-template-align.cpp -c
+
+; ModuleID = '/dir/test.cpp'
+source_filename = "/dir/test.cpp"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.myClass = type { i8 }
+; Function Attrs: noinline nounwind optnone uwtable
+define dso_local double @_ZN7myClass7findMaxEv(%struct.myClass* %this) #0 align 2 !dbg !7 {
+entry:
+  %this.addr = alloca %struct.myClass*, align 8
+  store %struct.myClass* %this, %struct.myClass** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %struct.myClass** %this.addr, metadata !17, metadata !DIExpression()), !dbg !19
+  %this1 = load %struct.myClass*, %struct.myClass** %this.addr, align 8
+  ret double 0.000000e+00, !dbg !20
+}
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+attributes #0 = { noinline nounwind optnone uwtable }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 10.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "/dir/test.cpp", directory: "/dir/", checksumkind: CSK_MD5, checksum: "4bed8955bd441e3129c12f557ed53962")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 5}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 10.0.0"}
+!7 = distinct !DISubprogram(name: "findMax", linkageName: "_ZN7myClass7findMaxEv", scope: !8, file: !1, line: 20, type: !9, scopeLine: 20, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, declaration: !13, retainedNodes: !2)
+!8 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "myClass", file: !1, line: 16, size: 8, flags: DIFlagTypePassByValue, elements: !2, identifier: "_ZTS7myClass")
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11, !12}
+!11 = !DIBasicType(name: "double", size: 64, encoding: DW_ATE_float)
+!12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!13 = !DISubprogram(name: "findMax", linkageName: "_ZN7myClass7findMaxEv", scope: !8, file: !1, line: 17, type: !14, scopeLine: 17, flags: DIFlagPrototyped, spFlags: 0)
+!14 = !DISubroutineType(types: !15)
+!15 = !{!16, !12}
+!16 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "auto")
+!17 = !DILocalVariable(name: "this", arg: 1, scope: !7, type: !18, flags: DIFlagArtificial | DIFlagObjectPointer)
+!18 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 64)
+!19 = !DILocation(line: 0, scope: !7)
+!20 = !DILocation(line: 21, column: 3, scope: !7)