Re-apply r292662, "IRGen: Start using the WriteThinLTOBitcode pass."

The internal build issue has been resolved.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@293231 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/BackendUtil.cpp

@@ -684,9 +684,11 @@ void EmitAssemblyHelper::EmitAssembly(BackendAction Action,
     break;
 
   case Backend_EmitBC:
-    PerModulePasses.add(createBitcodeWriterPass(
-        *OS, CodeGenOpts.EmitLLVMUseLists, CodeGenOpts.EmitSummaryIndex,
-        CodeGenOpts.EmitSummaryIndex));
+    if (CodeGenOpts.EmitSummaryIndex)
+      PerModulePasses.add(createWriteThinLTOBitcodePass(*OS));
+    else
+      PerModulePasses.add(
+          createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists));
     break;
 
   case Backend_EmitLL:

test/CMakeLists.txt

@@ -88,6 +88,7 @@ if( NOT CLANG_BUILT_STANDALONE )
     llvm-bcanalyzer
     llvm-cat
     llvm-dis
+    llvm-modextract
     llvm-nm
     llvm-objdump
     llvm-profdata

test/CodeGenCXX/type-metadata-thinlto.cpp

@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -flto=thin -flto-unit -triple x86_64-unknown-linux -fvisibility hidden -emit-llvm-bc -o %t %s
+// RUN: llvm-modextract -o - -n 1 %t | llvm-dis | FileCheck %s
+
+// CHECK: @_ZTV1A = linkonce_odr
+class A {
+  virtual void f() {}
+};
+
+A *f() {
+  return new A;
+}