Support for function summary index bitcode sections and files.

Summary:
The bitcode format is described in this document:
  https://drive.google.com/file/d/0B036uwnWM6RWdnBLakxmeDdOeXc/view
For more info on ThinLTO see:
  https://sites.google.com/site/llvmthinlto

The first customer is ThinLTO, however the data structures are designed
and named more generally based on prior feedback. There are a few
comments regarding how certain interfaces are used by ThinLTO, and the
options added here to gold currently have ThinLTO-specific names as the
behavior they provoke is currently ThinLTO-specific.

This patch includes support for generating per-module function indexes,
the combined index file via the gold plugin, and several tests
(more are included with the associated clang patch D11908).

Reviewers: dexonsmith, davidxl, joker.eph

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13107

llvm-svn: 249270

llvm/lib/Bitcode/Writer/BitcodeWriterPass.cpp

@@ -19,7 +19,7 @@
 using namespace llvm;
 
 PreservedAnalyses BitcodeWriterPass::run(Module &M) {
-  WriteBitcodeToFile(&M, OS, ShouldPreserveUseListOrder);
+  WriteBitcodeToFile(&M, OS, ShouldPreserveUseListOrder, EmitFunctionSummary);
   return PreservedAnalyses::all();
 }
 
@@ -27,17 +27,21 @@ namespace {
   class WriteBitcodePass : public ModulePass {
     raw_ostream &OS; // raw_ostream to print on
     bool ShouldPreserveUseListOrder;
+    bool EmitFunctionSummary;
 
   public:
     static char ID; // Pass identification, replacement for typeid
-    explicit WriteBitcodePass(raw_ostream &o, bool ShouldPreserveUseListOrder)
+    explicit WriteBitcodePass(raw_ostream &o, bool ShouldPreserveUseListOrder,
+                              bool EmitFunctionSummary)
         : ModulePass(ID), OS(o),
-          ShouldPreserveUseListOrder(ShouldPreserveUseListOrder) {}
+          ShouldPreserveUseListOrder(ShouldPreserveUseListOrder),
+          EmitFunctionSummary(EmitFunctionSummary) {}
 
     const char *getPassName() const override { return "Bitcode Writer"; }
 
     bool runOnModule(Module &M) override {
-      WriteBitcodeToFile(&M, OS, ShouldPreserveUseListOrder);
+      WriteBitcodeToFile(&M, OS, ShouldPreserveUseListOrder,
+                         EmitFunctionSummary);
       return false;
     }
   };
@@ -46,6 +50,8 @@ namespace {
 char WriteBitcodePass::ID = 0;
 
 ModulePass *llvm::createBitcodeWriterPass(raw_ostream &Str,
-                                          bool ShouldPreserveUseListOrder) {
-  return new WriteBitcodePass(Str, ShouldPreserveUseListOrder);
+                                          bool ShouldPreserveUseListOrder,
+                                          bool EmitFunctionSummary) {
+  return new WriteBitcodePass(Str, ShouldPreserveUseListOrder,
+                              EmitFunctionSummary);
 }