Add isHotBB helper function to ProfileSummaryInfo

Summary: This will unify all BB hotness checks.

Reviewers: eraman, davidxl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D26353

llvm-svn: 286415

include/llvm/Analysis/ProfileSummaryInfo.h

@@ -27,6 +27,8 @@
 #include <memory>
 
 namespace llvm {
+class BasicBlock;
+class BlockFrequencyInfo;
 class ProfileSummary;
 /// \brief Analysis providing profile information.
 ///
@@ -59,6 +61,8 @@ public:
   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.

lib/Analysis/ProfileSummaryInfo.cpp

@@ -12,7 +12,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#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"
@@ -121,6 +123,24 @@ bool ProfileSummaryInfo::isColdCount(uint64_t C) {
   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.
+  // The query currently has false positives as branch instruction cloning does
+  // not update/scale branch weights. Unlike false negatives, this will not cause
+  // performance problem.
+  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)