[CodeView] Add CodeView support for PGO debug information

[Holman]

Summary

This change adds debug information about whether PGO is being used or not.

Microsoft performance tooling (e.g. xperf, WPA) uses this information to show whether functions are optimized with PGO or not, as well as whether PGO information is invalid.

This information is useful for validating whether training scenarios are providing good coverage of real world scenarios, showing if profile data is out of date, etc.

[akhuang]

think this looks good overall; maybe it should also have an IR to codeview test?

[rnk]

IMO it's best to avoid adding fields to DICompileUnit if at all possible. It's the "god object" / "katamari damacy" of module debug info. Is there something about the IR module that indicates if PGO data is present or not? We could check that instead. I looked, but I wasn't able to find anything quickly.

[Holman]

In D99994#2677566, @rnk wrote:

IMO it's best to avoid adding fields to DICompileUnit if at all possible. It's the "god object" / "katamari damacy" of module debug info. Is there something about the IR module that indicates if PGO data is present or not? We could check that instead. I looked, but I wasn't able to find anything quickly.

Got it. It looks like MMI->getModule()->getProfileSummary() should have the info I need. I'll update to use that instead.

[Holman]

Get PGO info from Module instead of adding new field to debug info.

[rnk]

Seems reasonable, but we still need a small IR test.

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

807

nit, the more common style to name parameters looks like getProfileSummary(/*IsCS=*/false). Sort of more Python-y.

1434

I think the preferred spelling is GV.hasProfileData(), I think that's functionally equivalent.

[Holman]

Add a test

[Holman]

Fix clang-format issue.

[rnk]

lgtm, thanks!

[Holman]

Can someone help me get this checked in?

[rnk]

In D99994#2706515, @Holman wrote:

Can someone help me get this checked in?

Sure, I went ahead and pushed it.

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

void CodeViewDebug::emitCompilerInformation() {
 
   NamedMDNode *CUs = MMI->getModule()->getNamedMetadata("llvm.dbg.cu");
   const MDNode *Node = *CUs->operands().begin();
   const auto *CU = cast<DICompileUnit>(Node);
 
   // The low byte of the flags indicates the source language.
   Flags = MapDWLangToCVLang(CU->getSourceLanguage());
   // TODO:  Figure out which other flags need to be set.
+  if (MMI->getModule()->getProfileSummary(/* IsCS */ false) != nullptr) {
+    Flags |= static_cast<uint32_t>(CompileSym3Flags::PGO);
+  }
 
   OS.AddComment("Flags and language");
   OS.emitInt32(Flags);
 
   OS.AddComment("CPUType");
   OS.emitInt16(static_cast<uint64_t>(TheCPU));
 
   StringRef CompilerVersion = CU->getProducer();
if (GV.hasFnAttribute(Attribute::Naked))
     FPO |= FrameProcedureOptions::Naked;
   if (MFI.hasStackProtectorIndex())
     FPO |= FrameProcedureOptions::SecurityChecks;
   FPO |= FrameProcedureOptions(uint32_t(CurFn->EncodedLocalFramePtrReg) << 14U);
   FPO |= FrameProcedureOptions(uint32_t(CurFn->EncodedParamFramePtrReg) << 16U);
   if (Asm->TM.getOptLevel() != CodeGenOpt::None &&
       !GV.hasOptSize() && !GV.hasOptNone())
     FPO |= FrameProcedureOptions::OptimizedForSpeed;
+  if (GV.getEntryCount().hasValue()) {
+    FPO |= FrameProcedureOptions::ValidProfileCounts;
+    FPO |= FrameProcedureOptions::ProfileGuidedOptimization;
+  }
   // FIXME: Set GuardCfg when it is implemented.
   CurFn->FrameProcOpts = FPO;
 
   OS.EmitCVFuncIdDirective(CurFn->FuncId);
 
   // Find the end of the function prolog.  First known non-DBG_VALUE and
   // non-frame setup location marks the beginning of the function body.
   // FIXME: is there a simpler a way to do this? Can we just search