Add isHotBB helper function to ProfileSummaryInfo

[danielcdh]

Summary

This will unify all BB hotness checks.

[danielcdh]

update

[davidxl]

lib/Analysis/ProfileSummaryInfo.cpp

134

I think it is better to document the behavior this way:

The query currently has false positives as branch instruction cloning does not update/scale branch weights. Unlike false negatives, this won't cause performance problem.

[danielcdh]

update

[davidxl]

lgtm

include/llvm/Analysis/ProfileSummaryInfo.h

 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/ProfileSummary.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Pass.h"
 #include <memory>
 
 namespace llvm {
+class BasicBlock;
+class BlockFrequencyInfo;
 class ProfileSummary;
 /// \brief Analysis providing profile information.
 ///
 /// This is an immutable analysis pass that provides ability to query global
 /// (program-level) profile information. The main APIs are isHotCount and
 /// isColdCount that tells whether a given profile count is considered hot/cold
 /// based on the profile summary. This also provides convenience methods to
 /// check whether a function is hot or cold.
public:
   /// \brief Returns true if \p F has hot function entry.
   bool isFunctionEntryHot(const Function *F);
   /// \brief Returns true if \p F has cold function entry.
   bool isFunctionEntryCold(const Function *F);
   /// \brief Returns true if \p F is a hot function.
   bool isHotCount(uint64_t C);
   /// \brief Returns true if count \p C is considered cold.
   bool isColdCount(uint64_t C);
+  /// \brief Returns true if BasicBlock \p B is considered hot.
+  bool isHotBB(const BasicBlock *B, BlockFrequencyInfo *BFI);
 };
 
 /// An analysis pass based on legacy pass manager to deliver ProfileSummaryInfo.
 class ProfileSummaryInfoWrapperPass : public ImmutablePass {
   std::unique_ptr<ProfileSummaryInfo> PSI;
 
 public:
   static char ID;

lib/Analysis/ProfileSummaryInfo.cpp

 //===- ProfileSummaryInfo.cpp - Global profile summary information --------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains a pass that provides access to the global profile summary
 // information.
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/Analysis/BlockFrequencyInfo.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/ProfileSummary.h"
 using namespace llvm;
 
 // The following two parameters determine the threshold for a count to be
 // considered hot/cold. These two parameters are percentile values (multiplied
 // by 10000). If the counts are sorted in descending order, the minimum count to

 }
 
 bool ProfileSummaryInfo::isColdCount(uint64_t C) {
   if (!ColdCountThreshold)
     computeThresholds();
   return ColdCountThreshold && C <= ColdCountThreshold.getValue();
 }
 
+bool ProfileSummaryInfo::isHotBB(const BasicBlock *B, BlockFrequencyInfo *BFI) {
+  auto Count = BFI->getBlockProfileCount(B);
+  if (Count && isHotCount(*Count))
+    return true;
+  // Use extractProfTotalWeight to get BB count.
+  // For Sample PGO, BFI may not provide accurate BB count due to errors
+  // magnified during sample count propagation. This serves as a backup plan
+  // to ensure all hot BB will not be missed. Optimizations that clones code
+  // (e.g. inlining) need to update branch_probability to ensure
+  // extractProfTotalWeight is up-to-date. Otherwise, cold BB may be mis-labeled
+  // as hot by this function.
+  uint64_t TotalCount;
+  if (B->getTerminator()->extractProfTotalWeight(TotalCount) &&
+      isHotCount(TotalCount))
+    return true;
+  return false;
+}
+
 INITIALIZE_PASS(ProfileSummaryInfoWrapperPass, "profile-summary-info",
                 "Profile summary info", false, true)
 
 ProfileSummaryInfoWrapperPass::ProfileSummaryInfoWrapperPass()
     : ImmutablePass(ID) {
   initializeProfileSummaryInfoWrapperPassPass(*PassRegistry::getPassRegistry());
 }