[CodeView] Emit function types in -gline-tables-only.

[akhuang]

Summary

This change adds function types to further differentiate between
FUNC_IDs in -gline-tables-only.

Size increase of object files in clang are
Before: 917990 kb
After: 999312 kb

Bug: https://bugs.llvm.org/show_bug.cgi?id=48432

[rnk]

clang/lib/CodeGen/CGDebugInfo.cpp

1051–1052

We discussed giving lambdas display names as an alternative to doing this.

[akhuang]

Remove lambda change

[dblaikie]

clang/lib/CodeGen/CGDebugInfo.cpp

1051–1052

Should this be only for CodeView (due to CV's need for functions to be distinct in some way)? Adding the linkage name could increase debug info size for DWARF consumers unnecessarily

3740–3743

And here

[akhuang]

Add check for CodeView

clang/lib/CodeGen/CGDebugInfo.cpp

1051–1052

I think the CodeView change is elsewhere - here it just makes sure we only emit linkage names if it's not line tables only. (Now I'm remembering me creating the hasReducedDebugInfo function and the naming is pretty confusing...)

[dblaikie]

clang/test/CodeGenCXX/debug-info-gline-tables-only-codeview.cpp

31–33

This test doesn't seem related to the code change. Perhaps it's meant to test the "type:" parameter of the DISubprogram (like the type parameter of the DISubprogram for "m" is tested).

[akhuang]

clang/test/CodeGenCXX/debug-info-gline-tables-only-codeview.cpp

31–33

ah, yeah, it's not. I originally had a change for lambdas but took it out. I think I'll remove this part of the test for now.

[akhuang]

Update test

[dblaikie]

Looks good!

Might be worth some comments explaining why it's being done this way (probably good to have some details wherever we're making these changes to cope with CV's need for distinct functions by name/type/etc).

[akhuang]

Add comments describing reason for emitting types

[MaskRay]

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clang/lib/CodeGen/CGDebugInfo.cpp

CGDebugInfo::getOrCreateRecordFwdDecl(const RecordType *Ty,
   if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD))
     if (!CXXRD->hasDefinition() ||
         (CXXRD->hasDefinition() && !CXXRD->isTrivial()))
       Flags |= llvm::DINode::FlagNonTrivial;
 
   // Create the type.
   SmallString<256> Identifier;
   // Don't include a linkage name in line tables only.
   if (CGM.getCodeGenOpts().hasReducedDebugInfo())
     Identifier = getTypeIdentifier(Ty, CGM, TheCU);
   llvm::DICompositeType *RetTy = DBuilder.createReplaceableCompositeType(
       getTagForRecord(RD), RDName, Ctx, DefUnit, Line, 0, Size, Align, Flags,
       Identifier);
   if (CGM.getCodeGenOpts().DebugFwdTemplateParams)
     if (auto *TSpecial = dyn_cast<ClassTemplateSpecializationDecl>(RD))
       DBuilder.replaceArrays(RetTy, llvm::DINodeArray(),
                              CollectCXXTemplateParams(TSpecial, DefUnit));
   ReplaceMap.emplace_back(
static bool shouldOmitDefinition(codegenoptions::DebugInfoKind DebugKind,
                                  const LangOptions &LangOpts) {
   if (DebugTypeExtRefs && isDefinedInClangModule(RD->getDefinition()))
     return true;
 
   if (auto *ES = RD->getASTContext().getExternalSource())
     if (ES->hasExternalDefinitions(RD) == ExternalASTSource::EK_Always)
       return true;
 
+  // Only emit forward declarations in line tables only to keep debug info size
+  // small. This only applies to CodeView, since we don't emit types in DWARF
+  // line tables only.
   if (DebugKind == codegenoptions::DebugLineTablesOnly)
     return true;
 
   if (DebugKind > codegenoptions::LimitedDebugInfo)
     return false;
 
   if (!LangOpts.CPlusPlus)
     return false;
llvm::DISubprogram *CGDebugInfo::getObjCMethodDeclaration(
   return FD;
 }
 
 // getOrCreateFunctionType - Construct type. If it is a c++ method, include
 // implicit parameter "this".
 llvm::DISubroutineType *CGDebugInfo::getOrCreateFunctionType(const Decl *D,
                                                              QualType FnType,
                                                              llvm::DIFile *F) {
-  if (!D || DebugKind <= codegenoptions::DebugLineTablesOnly)
+  // In CodeView, we emit the function types in line tables only because the
+  // only way to distinguish between functions is by display name and type.
+  if (!D || (DebugKind <= codegenoptions::DebugLineTablesOnly &&
+             !CGM.getCodeGenOpts().EmitCodeView))
     // Create fake but valid subroutine type. Otherwise -verify would fail, and
     // subprogram DIE will miss DW_AT_decl_file and DW_AT_decl_line fields.
     return DBuilder.createSubroutineType(DBuilder.getOrCreateTypeArray(None));
 
   if (const auto *Method = dyn_cast<CXXMethodDecl>(D))
     return getOrCreateMethodType(Method, F, false);
 
   const auto *FTy = FnType->getAs<FunctionType>();

clang/test/CodeGenCXX/debug-info-gline-tables-only-codeview.cpp

 // RUN: %clang_cc1 %s -gcodeview -debug-info-kind=line-tables-only -S \
 // RUN:   -emit-llvm -o - | FileCheck %s
 // Checks that clang with "-gline-tables-only" with CodeView emits some debug
 // info for variables and types when they appear in function scopes.
 
 namespace NS {
 struct C {
-public:
   void m() {}
 };
 void f() {}
 }
 
 NS::C c;
 
 void test() {
-  // CHECK: ![[EMPTY:[0-9]+]] = !{}
   // CHECK: !DISubprogram(name: "f", scope: ![[NS:[0-9]+]],
   // CHECK-SAME:          type: ![[F:[0-9]+]]
   // CHECK: ![[NS]] = !DINamespace(name: "NS", scope: null)
-  // CHECK: ![[F]] = !DISubroutineType(types: ![[EMPTY]])
+  // CHECK: ![[F]] = !DISubroutineType(types: ![[FTYPE:[0-9]+]])
+  // CHECK: ![[FTYPE]] = !{null}
   NS::f();
 
-  // CHECK: !DISubprogram(name: "m", scope: ![[C:[0-9]+]],
-  // CHECK-SAME:          type: ![[F]]
+  // CHECK: ![[M:[0-9]+]] = distinct !DISubprogram(name: "m", scope: ![[C:[0-9]+]],
+  // CHECK-SAME:                                   type: ![[MTYPE:[0-9]+]]
   // CHECK: ![[C]] = !DICompositeType(tag: DW_TAG_structure_type, name: "C",
   // CHECK-SAME:                      flags: DIFlagFwdDecl
   // CHECK-NOT: identifier
+  // CHECK: ![[MTYPE]] = !DISubroutineType(types: !{{.*}})
   c.m();
 }