[PM] Add support for instrumented PGO in the new pass manager (clang-side)

[davide]

Summary

This implements the clang bits of https://reviews.llvm.org/D29308
I'm planning to use this to test the PGO inliner changes available only in the new pass manager.
I'm not very familiar with the clang driver so I'm not sure if this change is correct. PTAL (also suggestions on how to best test this are welcome).

[davidxl]

lib/CodeGen/BackendUtil.cpp

823

can you define a macro for the default profile file name to be shared?

[davide]

lib/CodeGen/BackendUtil.cpp

823

Sure thing. I generally prefer a global const std::string (trying to avoid macros), is that the same to you?

[davide]

Thanks. I'll update a new version shortly. The llvm side of the patch is slightly more interesting as I made some assumptions (and I still am learning about PGO so I'm not entirely sure I put in the correct place in the pipeline)

[chandlerc]

lib/CodeGen/BackendUtil.cpp

823

Global std::string objects are problematic due to the destructor.

But we just recently added a handy string literal type to LLVM. =]

[davide]

Addressed comments. Thanks!

[davide]

lib/CodeGen/BackendUtil.cpp

63–65

FWIW, this was part of AssemblyHelper initially.
I thought that worked, instead I got a linker error (undefined reference to etc..)
I can't claim to be a C++ expert so I asked @Bigcheese and he pointed out this could actually be a bug in clang.

[davide]

lib/CodeGen/BackendUtil.cpp

63–65

Just for the records, not a clang bug, it's missing an out-of-line def (thanks zygoloid for pointing out)

[chandlerc]

FWIW, this all looks good on my end. David, does this address your concern?

lib/CodeGen/BackendUtil.cpp

63–65

As discussed in IRC, looks like we know how to sink this into the class now.

lib/CodeGen/BackendUtil.cpp

 #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;
 
 namespace {
 
+// Default filename used for profile generation.
+static constexpr StringLiteral DefaultProfileGenName = "default_%m.profraw";
+
 class EmitAssemblyHelper {
   DiagnosticsEngine &Diags;
   const HeaderSearchOptions &HSOpts;
   const CodeGenOptions &CodeGenOpts;
   const clang::TargetOptions &TargetOpts;
   const LangOptions &LangOpts;
   Module *TheModule;
 
if (CodeGenOpts.hasProfileClangInstr()) {
     Options.InstrProfileOutput = CodeGenOpts.InstrProfileOutput;
     MPM.add(createInstrProfilingLegacyPass(Options));
   }
   if (CodeGenOpts.hasProfileIRInstr()) {
     PMBuilder.EnablePGOInstrGen = true;
     if (!CodeGenOpts.InstrProfileOutput.empty())
       PMBuilder.PGOInstrGen = CodeGenOpts.InstrProfileOutput;
     else
-      PMBuilder.PGOInstrGen = "default_%m.profraw";
+      PMBuilder.PGOInstrGen = DefaultProfileGenName;
   }
   if (CodeGenOpts.hasProfileIRUse())
     PMBuilder.PGOInstrUse = CodeGenOpts.ProfileInstrumentUsePath;
 
   if (!CodeGenOpts.SampleProfileFile.empty())
     PMBuilder.PGOSampleUse = CodeGenOpts.SampleProfileFile;
 
   PMBuilder.populateFunctionPassManager(FPM);
void EmitAssemblyHelper::EmitAssemblyWithNewPassManager(
   // The new pass manager always makes a target machine available to passes
   // during construction.
   CreateTargetMachine(/*MustCreateTM*/ true);
   if (!TM)
     // This will already be diagnosed, just bail.
     return;
   TheModule->setDataLayout(TM->createDataLayout());
 
-  PassBuilder PB(TM.get());
+  PGOOptions PGOOpt;
+
+  // -fprofile-generate.
+  PGOOpt.RunProfileGen = CodeGenOpts.hasProfileIRInstr();
+  if (PGOOpt.RunProfileGen)
+    PGOOpt.ProfileGenFile = CodeGenOpts.InstrProfileOutput.empty() ?
+      DefaultProfileGenName : CodeGenOpts.InstrProfileOutput;
+
+  // -fprofile-use.
+  if (CodeGenOpts.hasProfileIRUse())
+    PGOOpt.ProfileUseFile = CodeGenOpts.ProfileInstrumentUsePath;
+
+  // Only pass a PGO options struct if -fprofile-generate or
+  // -fprofile-use were passed on the cmdline.
+  PassBuilder PB(TM.get(),
+    (PGOOpt.RunProfileGen ||
+      !PGOOpt.ProfileUseFile.empty()) ? &PGOOpt : nullptr);
 
   LoopAnalysisManager LAM;
   FunctionAnalysisManager FAM;
   CGSCCAnalysisManager CGAM;
   ModuleAnalysisManager MAM;
 
   // Register the AA manager first so that our version is the one used.
   FAM.registerPass([&] { return PB.buildDefaultAAPipeline(); });
 
   // Register all the basic analyses with the managers.
   PB.registerModuleAnalyses(MAM);
   PB.registerCGSCCAnalyses(CGAM);
   PB.registerFunctionAnalyses(FAM);
   PB.registerLoopAnalyses(LAM);
   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
 
   ModulePassManager MPM;
 
   if (!CodeGenOpts.DisableLLVMPasses) {
     if (CodeGenOpts.OptimizationLevel == 0) {
       // Build a minimal pipeline based on the semantics required by Clang,
       // which is just that always inlining occurs.
       MPM.addPass(AlwaysInlinerPass());
     } else {
       // Otherwise, use the default pass pipeline. We also have to map our
       // optimization levels into one of the distinct levels used to configure
       // the pipeline.
       PassBuilder::OptimizationLevel Level = mapToLevel(CodeGenOpts);
 
       MPM = PB.buildPerModuleDefaultPipeline(Level);
     }
   }