[BOLT][NFC] Add post-CFG processing to MetadataRewriter interface

[maksfb]

Summary

Add MetadataRewriter::postCFGInitializer().

Depends on D154815

bolt/include/bolt/Rewrite/MetadataManager.h

 public:
   /// Register a new \p Rewriter.
   void registerRewriter(std::unique_ptr<MetadataRewriter> Rewriter);
 
   /// Execute initialization of rewriters while functions are disassembled, but
   /// CFG is not yet built.
   void runInitializersPreCFG();
 
+  /// Execute metadata initializers after CFG was constructed for functions.
+  void runInitializersPostCFG();
+
   /// Run finalization step of rewriters after code has been emitted.
   void runFinalizersAfterEmit();
 };
 
 } // namespace bolt
 } // namespace llvm
 
 #endif // BOLT_REWRITE_METADATA_MANAGER_H

bolt/include/bolt/Rewrite/MetadataRewriter.h

public:
 
   /// Return name for the rewriter.
   StringRef getName() const { return Name; }
 
   /// Interface for modifying/annotating functions in the binary based on the
   /// contents of the section. Functions are in pre-cfg state.
   virtual Error preCFGInitializer() { return Error::success(); }
 
+  /// Run the rewriter once the functions are in CFG state.
+  virtual Error postCFGInitializer() { return Error::success(); }
+
   /// Finalize section contents based on the new context after the new code is
   /// emitted.
   virtual Error postEmitFinalizer() { return Error::success(); }
 };
 
 } // namespace bolt
 } // namespace llvm
 
 #endif // BOLT_REWRITE_METADATA_REWRITER_H

bolt/include/bolt/Rewrite/RewriteInstance.h

private:
   void emitAndLink();
 
   /// Link additional runtime code to support instrumentation.
   void linkRuntime();
 
   /// Process metadata in special sections before CFG is built for functions.
   void processMetadataPreCFG();
 
+  /// Process metadata in special sections after CFG is built for functions.
+  void processMetadataPostCFG();
+
   /// Update debug and other auxiliary information in the file.
   void updateMetadata();
 
   /// Return the list of code sections in the output order.
   std::vector<BinarySection *> getCodeSections();
 
   /// Map all sections to their final addresses.
   void mapFileSections(BOLTLinker::SectionMapper MapSection);

bolt/lib/Rewrite/MetadataManager.cpp

for (auto &Rewriter : Rewriters) {
     if (Error E = Rewriter->preCFGInitializer()) {
       errs() << "BOLT-ERROR: while running " << Rewriter->getName()
              << " in pre-CFG state: " << toString(std::move(E)) << '\n';
       exit(1);
     }
   }
 }
 
+void MetadataManager::runInitializersPostCFG() {
+  for (auto &Rewriter : Rewriters) {
+    LLVM_DEBUG(dbgs() << "BOLT-DEBUG: invoking " << Rewriter->getName()
+                      << " after CFG construction\n");
+    if (Error E = Rewriter->postCFGInitializer()) {
+      errs() << "BOLT-ERROR: while running " << Rewriter->getName()
+             << " in CFG state: " << toString(std::move(E)) << '\n';
+      exit(1);
+    }
+  }
+}
+
 void MetadataManager::runFinalizersAfterEmit() {
   for (auto &Rewriter : Rewriters) {
     LLVM_DEBUG(dbgs() << "BOLT-DEBUG: invoking " << Rewriter->getName()
                       << " after emit\n");
     if (Error E = Rewriter->postEmitFinalizer()) {
       errs() << "BOLT-ERROR: while running " << Rewriter->getName()
              << " after emit: " << toString(std::move(E)) << '\n';
       exit(1);
     }
   }
 }

bolt/lib/Rewrite/RewriteInstance.cpp

Error RewriteInstance::run() {
   processMetadataPreCFG();
 
   buildFunctionsCFG();
 
   processProfileData();
 
   postProcessFunctions();
 
+  processMetadataPostCFG();
+
   if (opts::DiffOnly)
     return Error::success();
 
   preregisterSections();
 
   runOptimizationPasses();
 
   emitAndLink();

 void RewriteInstance::processMetadataPreCFG() {
   initializeMetadataManager();
 
   MetadataManager.runInitializersPreCFG();
 
   processProfileDataPreCFG();
 }
 
+void RewriteInstance::processMetadataPostCFG() {
+  MetadataManager.runInitializersPostCFG();
+}
+
 void RewriteInstance::processProfileDataPreCFG() {
   if (!ProfileReader)
     return;
 
   NamedRegionTimer T("processprofile-precfg", "process profile data pre-CFG",
                      TimerGroupName, TimerGroupDesc, opts::TimeRewrite);
 
   if (Error E = ProfileReader->readProfilePreCFG(*BC.get()))