[CSSPGO] Turn on iterative-BFI for CSSPGO

[wenlei]

Summary

Iterative-BFI produces better count quality and performance when evaluated on internal benchmarks. Turning it on by default now for CSSPGO. We can consider turn it on by default for AutoFDO as well in the future.

[wlei]

LGTM, thanks!

llvm/lib/Transforms/IPO/SampleProfile.cpp

1808

Nit: default

[wenlei]

fix typo

[hoy]

lgtm, thx.

llvm/lib/Transforms/IPO/SampleProfile.cpp

 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
 #include "llvm/Analysis/CallGraph.h"
 #include "llvm/Analysis/CallGraphSCCPass.h"
 #include "llvm/Analysis/InlineAdvisor.h"
 #include "llvm/Analysis/InlineCost.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/PostDominators.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
if (Reader->profileIsCS()) {
     FunctionSamples::ProfileIsCS = true;
 
     // Enable priority-base inliner and size inline by default for CSSPGO.
     if (!ProfileSizeInline.getNumOccurrences())
       ProfileSizeInline = true;
     if (!CallsitePrioritizedInline.getNumOccurrences())
       CallsitePrioritizedInline = true;
 
+    // Enable iterative-BFI by default for CSSPGO.
+    if (!UseIterativeBFIInference.getNumOccurrences())
+      UseIterativeBFIInference = true;
+
     // Tracker for profiles under different context
     ContextTracker =
         std::make_unique<SampleContextTracker>(Reader->getProfiles());
   }
 
   // Load pseudo probe descriptors for probe-based function samples.
   if (Reader->profileIsProbeBased()) {
     ProbeManager = std::make_unique<PseudoProbeManager>(M);