make -fmodules-codegen and -fmodules-debuginfo work also with PCHs

Allow to build PCH's (with -building-pch-with-obj and the extra .o file)
with -fmodules-codegen -fmodules-debuginfo to allow emitting shared code
into the extra .o file, similarly to how it works with modules. A bit of
a misnomer, but the underlying functionality is the same. This saves up
to 20% of build time here. The patch is fairly simple, it basically just
duplicates -fmodules checks to also alternatively check
-building-pch-with-obj.

This already got committed as cbc9d22e49,
but then got reverted in 7ea9a6e022
because of PR44953, as discussed in D74846. This is a corrected version
which does not include two places for the PCH case that aren't included
in the modules -fmodules-codegen path either.

Differential Revision: https://reviews.llvm.org/D69778

clang/lib/Serialization/ASTReader.cpp

@@ -3234,7 +3234,8 @@ ASTReader::ReadASTBlock(ModuleFile &F, unsigned ClientLoadCapabilities) {
     case MODULAR_CODEGEN_DECLS:
       // FIXME: Skip reading this record if our ASTConsumer doesn't care about
       // them (ie: if we're not codegenerating this module).
-      if (F.Kind == MK_MainFile)
+      if (F.Kind == MK_MainFile ||
+          getContext().getLangOpts().BuildingPCHWithObjectFile)
         for (unsigned I = 0, N = Record.size(); I != N; ++I)
           EagerlyDeserializedDecls.push_back(getGlobalDeclID(F, Record[I]));
       break;

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -503,8 +503,12 @@ uint64_t ASTDeclReader::GetCurrentCursorOffset() {
 }
 
 void ASTDeclReader::ReadFunctionDefinition(FunctionDecl *FD) {
-  if (Record.readInt())
+  if (Record.readInt()) {
     Reader.DefinitionSource[FD] = Loc.F->Kind == ModuleKind::MK_MainFile;
+    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
+        Reader.DeclIsFromPCHWithObjectFile(FD))
+      Reader.DefinitionSource[FD] = true;
+  }
   if (auto *CD = dyn_cast<CXXConstructorDecl>(FD)) {
     CD->setNumCtorInitializers(Record.readInt());
     if (CD->getNumCtorInitializers())
@@ -1431,8 +1435,12 @@ ASTDeclReader::RedeclarableResult ASTDeclReader::VisitVarDeclImpl(VarDecl *VD) {
       Reader.getContext().setBlockVarCopyInit(VD, CopyExpr, Record.readInt());
   }
 
-  if (VD->getStorageDuration() == SD_Static && Record.readInt())
+  if (VD->getStorageDuration() == SD_Static && Record.readInt()) {
     Reader.DefinitionSource[VD] = Loc.F->Kind == ModuleKind::MK_MainFile;
+    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
+        Reader.DeclIsFromPCHWithObjectFile(VD))
+      Reader.DefinitionSource[VD] = true;
+  }
 
   enum VarKind {
     VarNotTemplate = 0, VarTemplate, StaticDataMemberSpecialization
@@ -1691,8 +1699,12 @@ void ASTDeclReader::ReadCXXDefinitionData(
   Data.ODRHash = Record.readInt();
   Data.HasODRHash = true;
 
-  if (Record.readInt())
+  if (Record.readInt()) {
     Reader.DefinitionSource[D] = Loc.F->Kind == ModuleKind::MK_MainFile;
+    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
+        Reader.DeclIsFromPCHWithObjectFile(D))
+      Reader.DefinitionSource[D] = true;
+  }
 
   Data.NumBases = Record.readInt();
   if (Data.NumBases)

clang/lib/Serialization/ASTWriter.cpp

@@ -5688,8 +5688,8 @@ void ASTRecordWriter::AddCXXDefinitionData(const CXXRecordDecl *D) {
 
   // getODRHash will compute the ODRHash if it has not been previously computed.
   Record->push_back(D->getODRHash());
-  bool ModulesDebugInfo = Writer->Context->getLangOpts().ModulesDebugInfo &&
-                          Writer->WritingModule && !D->isDependentType();
+  bool ModulesDebugInfo =
+      Writer->Context->getLangOpts().ModulesDebugInfo && !D->isDependentType();
   Record->push_back(ModulesDebugInfo);
   if (ModulesDebugInfo)
     Writer->ModularCodegenDecls.push_back(Writer->GetDeclRef(D));

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -2458,9 +2458,10 @@ void ASTRecordWriter::AddFunctionDefinition(const FunctionDecl *FD) {
 
   assert(FD->doesThisDeclarationHaveABody());
   bool ModulesCodegen = false;
-  if (Writer->WritingModule && !FD->isDependentContext()) {
+  if (!FD->isDependentContext()) {
     Optional<GVALinkage> Linkage;
-    if (Writer->WritingModule->Kind == Module::ModuleInterfaceUnit) {
+    if (Writer->WritingModule &&
+        Writer->WritingModule->Kind == Module::ModuleInterfaceUnit) {
       // When building a C++ Modules TS module interface unit, a strong
       // definition in the module interface is provided by the compilation of
       // that module interface unit, not by its users. (Inline functions are

clang/test/Modules/Inputs/codegen-flags/foo.h

@@ -1,4 +1,7 @@
+#ifndef FOO_H
+#define FOO_H
 struct foo {
 };
 inline void f1() {
 }
+#endif

clang/test/PCH/codegen.cpp

@@ -0,0 +1,42 @@
+// This test is the PCH version of Modules/codegen-flags.test . It uses its inputs.
+// The purpose of this test is just verify that the codegen options work with PCH as well.
+// All the codegen functionality should be tested in Modules/.
+
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// REQUIRES: x86-registered-target
+
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -fmodules-codegen -x c++-header -building-pch-with-obj -emit-pch %S/../Modules/Inputs/codegen-flags/foo.h -o %t/foo-cg.pch
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -fmodules-debuginfo -x c++-header -building-pch-with-obj -emit-pch %S/../Modules/Inputs/codegen-flags/foo.h -o %t/foo-di.pch
+
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -debug-info-kind=limited -o - %s -include-pch %t/foo-cg.pch -building-pch-with-obj -fmodules-codegen | FileCheck --check-prefix=CG %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -debug-info-kind=limited -o - %s -include-pch %t/foo-di.pch -building-pch-with-obj -fmodules-debuginfo | FileCheck --check-prefix=DI %s
+
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -debug-info-kind=limited -o - -include-pch %t/foo-cg.pch %S/../Modules/Inputs/codegen-flags/use.cpp | FileCheck --check-prefix=CG-USE %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -debug-info-kind=limited -o - -include-pch %t/foo-di.pch %S/../Modules/Inputs/codegen-flags/use.cpp | FileCheck --check-prefix=DI-USE %s
+
+// Test with template instantiation in the pch.
+
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -fmodules-codegen -x c++-header -building-pch-with-obj -emit-pch -fpch-instantiate-templates %S/../Modules/Inputs/codegen-flags/foo.h -o %t/foo-cg.pch
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -fmodules-debuginfo -x c++-header -building-pch-with-obj -emit-pch -fpch-instantiate-templates %S/../Modules/Inputs/codegen-flags/foo.h -o %t/foo-di.pch
+
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -debug-info-kind=limited -o - %s -include-pch %t/foo-cg.pch -building-pch-with-obj -fmodules-codegen | FileCheck --check-prefix=CG %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -debug-info-kind=limited -o - %s -include-pch %t/foo-di.pch -building-pch-with-obj -fmodules-debuginfo | FileCheck --check-prefix=DI %s
+
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -debug-info-kind=limited -o - -include-pch %t/foo-cg.pch %S/../Modules/Inputs/codegen-flags/use.cpp | FileCheck --check-prefix=CG-USE %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -debug-info-kind=limited -o - -include-pch %t/foo-di.pch %S/../Modules/Inputs/codegen-flags/use.cpp | FileCheck --check-prefix=DI-USE %s
+
+
+// CG: define weak_odr void @_Z2f1v
+// CG: DICompileUnit
+// CG-NOT: DICompositeType
+
+// CG-USE: declare void @_Z2f1v
+// CG-USE: DICompileUnit
+// CG-USE: distinct !DICompositeType(tag: DW_TAG_structure_type, name: "foo"
+
+// DI-NOT: define
+// DI: distinct !DICompositeType(tag: DW_TAG_structure_type, name: "foo"
+
+// DI-USE: define linkonce_odr void @_Z2f1v
+// DI-USE: = !DICompositeType(tag: DW_TAG_structure_type, name: "foo", {{.*}}, flags: DIFlagFwdDecl