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

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

Differential Revision: https://reviews.llvm.org/D95001

Author: amykhuang

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -2317,6 +2317,9 @@ static bool shouldOmitDefinition(codegenoptions::DebugInfoKind DebugKind,
     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;
 
@@ -3726,7 +3729,10 @@ llvm::DISubprogram *CGDebugInfo::getObjCMethodDeclaration(
 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));

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

@@ -5,7 +5,6 @@
 
 namespace NS {
 struct C {
-public:
   void m() {}
 };
 void f() {}
@@ -14,17 +13,18 @@ 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();
 }