Call TargetMachine::addEarlyAsPossiblePasses from BackendUtil.

[jlebar]

Summary

As of D18614, TargetMachine exposes a hook to add a set of passes that should
be run as early as possible. Invoke this hook from clang when setting up the
pass manager.

[chandlerc]

Minor tweak, but with that LGTM once the LLVM side is in place.

lib/CodeGen/BackendUtil.cpp

347

Why capture this? Capturing TM would seem narrower. If you don't want a narrow capture, I'd just use [&]...

[jlebar]

lib/CodeGen/BackendUtil.cpp

347

TM is a member variable; you can't explicitly capture member variables? https://godbolt.org/g/T4kl3G

I can change it to [&] if you like that better.

[jlebar]

Switch [this] to [&].

[chandlerc]

lib/CodeGen/BackendUtil.cpp

347

Wow, C++ is silly here. You can't capture it *by value*. You have to use an init capture (which we can't use yet). How silly. Anyways, thanks for the explanation.

lib/CodeGen/BackendUtil.cpp

void EmitAssemblyHelper::CreatePasses(ModuleSummaryIndex *ModuleSummary) {
   // If we are performing a ThinLTO importing compile, invoke the LTO
   // pipeline and pass down the in-memory module summary index.
   if (ModuleSummary) {
     PMBuilder.ModuleSummary = ModuleSummary;
     PMBuilder.populateThinLTOPassManager(*MPM);
     return;
   }
 
+  // Add target-specific passes that need to run as early as possible.
+  if (TM)
+    PMBuilder.addExtension(
+        PassManagerBuilder::EP_EarlyAsPossible,
+        [this](const PassManagerBuilder &, legacy::PassManagerBase &PM) {
+          TM->addEarlyAsPossiblePasses(PM);
+        });
+
   PMBuilder.addExtension(PassManagerBuilder::EP_EarlyAsPossible,
                          addAddDiscriminatorsPass);
 
   // In ObjC ARC mode, add the main ARC optimization passes.
   if (LangOpts.ObjCAutoRefCount) {
     PMBuilder.addExtension(PassManagerBuilder::EP_EarlyAsPossible,
                            addObjCARCExpandPass);
     PMBuilder.addExtension(PassManagerBuilder::EP_ModuleOptimizerEarly,