Add LoopSink pass for PGO.

[danielcdh]

Summary

PGO has accurate profile info that can be used to enable LoopSink pass

[davidxl]

lib/CodeGen/BackendUtil.cpp

156

Is this pass strictly needed?

[danielcdh]

add comment why we need inst simplify

[danielcdh]

We need this pass to remove LCSSA nodes because this will be the last loop pass.

Another question is: shall we pin this pass to PGO only? If not, we can simply add it to lib/Transforms/IPO/PassManagerBuilder.cpp

[danielcdh]

Close this revision and a new patch has be sent: https://reviews.llvm.org/D26155

lib/CodeGen/BackendUtil.cpp

if (Builder.OptLevel > 0)
     PM.add(createObjCARCOptPass());
 }
 
 static void addAddDiscriminatorsPass(const PassManagerBuilder &Builder,
                                      legacy::PassManagerBase &PM) {
   PM.add(createAddDiscriminatorsPass());
 }
 
+static void addPGOOnlyOptimizations(
+    const PassManagerBuilder &Builder, legacy::PassManagerBase &PM) {
+  PM.add(createLoopSinkPass());
+  // Get rid of LCSSA nodes.
+  PM.add(createInstructionSimplifierPass());
+}
+
 static void addBoundsCheckingPass(const PassManagerBuilder &Builder,
                                   legacy::PassManagerBase &PM) {
   PM.add(createBoundsCheckingPass());
 }
 
 static void addSanitizerCoveragePass(const PassManagerBuilder &Builder,
                                      legacy::PassManagerBase &PM) {
   const PassManagerBuilderWrapper &BuilderWrapper =
void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
   if (CodeGenOpts.hasProfileIRUse())
     PMBuilder.PGOInstrUse = CodeGenOpts.ProfileInstrumentUsePath;
 
   if (!CodeGenOpts.SampleProfileFile.empty()) {
     MPM.add(createPruneEHPass());
     MPM.add(createSampleProfileLoaderPass(CodeGenOpts.SampleProfileFile));
   }
 
+  if (!CodeGenOpts.SampleProfileFile.empty() || CodeGenOpts.hasProfileIRUse())
+    PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
+                           addPGOOnlyOptimizations);
+
   PMBuilder.populateFunctionPassManager(FPM);
   PMBuilder.populateModulePassManager(MPM);
 }
 
 void EmitAssemblyHelper::setCommandLineOpts() {
   SmallVector<const char *, 16> BackendArgs;
   BackendArgs.push_back("clang"); // Fake program name.
   if (!CodeGenOpts.DebugPass.empty()) {