[ThinLTO] Wire up ThinLTO and new PM

[timshen]

Summary

This patch teaches clang to use and propagate new PM in ThinLTO

[timshen]

Rebase the patch onto D33799.

[chandlerc]

This patch LGTM whenever the underlying LLVM change lands, thanks!!!!

[davide]

LGTM once the other patch lands.

clang/lib/CodeGen/BackendUtil.cpp

 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetOptions.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include "llvm/Transforms/Coroutines.h"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/IPO/AlwaysInliner.h"
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
+#include "llvm/Transforms/IPO/ThinLTOBitcodeWriter.h"
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/ObjCARC.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Scalar/GVN.h"
 #include "llvm/Transforms/Utils/SymbolRewriter.h"
 #include <memory>
 using namespace clang;
 using namespace llvm;
if (CodeGenOpts.OptimizationLevel == 0) {
       MPM = PB.buildPerModuleDefaultPipeline(Level);
     }
   }
 
   // FIXME: We still use the legacy pass manager to do code generation. We
   // create that pass manager here and use it as needed below.
   legacy::PassManager CodeGenPasses;
   bool NeedCodeGen = false;
+  Optional<raw_fd_ostream> ThinLinkOS;
 
   // Append any output we need to the pass manager.
   switch (Action) {
   case Backend_EmitNothing:
     break;
 
   case Backend_EmitBC:
+    if (CodeGenOpts.EmitSummaryIndex) {
+      if (!CodeGenOpts.ThinLinkBitcodeFile.empty()) {
+        std::error_code EC;
+        ThinLinkOS.reset(raw_fd_ostream(CodeGenOpts.ThinLinkBitcodeFile, EC,
+                                        llvm::sys::fs::F_None));
+        if (EC) {
+          Diags.Report(diag::err_fe_unable_to_open_output)
+              << CodeGenOpts.ThinLinkBitcodeFile << EC.message();
+          return;
+        }
+      }
+      MPM.addPass(
+          ThinLTOBitcodeWriterPass(*OS, ThinLinkOS ? &*ThinLinkOS : nullptr));
+    } else {
       MPM.addPass(BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
                                     CodeGenOpts.EmitSummaryIndex,
                                     CodeGenOpts.EmitSummaryIndex));
+    }
     break;
 
   case Backend_EmitLL:
     MPM.addPass(PrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists));
     break;
 
   case Backend_EmitAssembly:
   case Backend_EmitMCNull:

clang/test/CodeGen/thin_link_bitcode.c

 // RUN: %clang_cc1 -o %t -flto=thin -fthin-link-bitcode=%t.nodebug -triple x86_64-unknown-linux-gnu -emit-llvm-bc -debug-info-kind=limited %s
 // RUN: llvm-bcanalyzer -dump %t | FileCheck %s
 // RUN: llvm-bcanalyzer -dump %t.nodebug | FileCheck %s --check-prefix=NO_DEBUG
+// RUN: %clang_cc1 -o %t.newpm -flto=thin -fexperimental-new-pass-manager -fthin-link-bitcode=%t.newpm.nodebug -triple x86_64-unknown-linux-gnu -emit-llvm-bc -debug-info-kind=limited  %s
+// RUN: llvm-bcanalyzer -dump %t.newpm | FileCheck %s
+// RUN: llvm-bcanalyzer -dump %t.newpm.nodebug | FileCheck %s --check-prefix=NO_DEBUG
 int main (void) {
   return 0;
 }
 
 // CHECK: COMPILE_UNIT
 // NO_DEBUG-NOT: COMPILE_UNIT