[PATCH] D30800: Do not use branch metadata to check if a basic block is hot.

[Dehao Chen via Phabricator via llvm-commits]

danielcdh created this revision.

We should not use that to check basic block hotness as optimization may mess it up.


https://reviews.llvm.org/D30800

Files:
  lib/Analysis/ProfileSummaryInfo.cpp
  unittests/Analysis/ProfileSummaryInfoTest.cpp


Index: unittests/Analysis/ProfileSummaryInfoTest.cpp
===================================================================
--- unittests/Analysis/ProfileSummaryInfoTest.cpp
+++ unittests/Analysis/ProfileSummaryInfoTest.cpp
@@ -162,12 +162,6 @@
 
   EXPECT_TRUE(PSI.isHotCallSite(CS1, &BFI));
   EXPECT_FALSE(PSI.isHotCallSite(CS2, &BFI));
-
-  // Test that adding an MD_prof metadata with a hot count on CS2 does not
-  // change itas hotness as it has no effect in instrumented profiling.
-  MDBuilder MDB(M->getContext());
-  CI2->setMetadata(llvm::LLVMContext::MD_prof, MDB.createBranchWeights({400}));
-  EXPECT_FALSE(PSI.isHotCallSite(CS2, &BFI));
 }
 
 TEST_F(ProfileSummaryInfoTest, SampleProf) {
Index: lib/Analysis/ProfileSummaryInfo.cpp
===================================================================
--- lib/Analysis/ProfileSummaryInfo.cpp
+++ lib/Analysis/ProfileSummaryInfo.cpp
@@ -124,18 +124,7 @@
 
 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;
-  auto *TI = B->getTerminator();
-  return extractProfTotalWeight(TI, TotalCount) && isHotCount(TotalCount);
+  return Count && isHotCount(*Count);
 }
 
 bool ProfileSummaryInfo::isColdBB(const BasicBlock *B,


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