Do not use branch metadata to check if a basic block is hot.

[danielcdh]

Summary

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

[eraman]

LGTM after removing the changes to the ProfileSummaryInfoTest.cpp.

unittests/Analysis/ProfileSummaryInfoTest.cpp

165

This test is still relevant even after the change. I think you meant to remove it in the other patch - https://reviews.llvm.org/D30799

lib/Analysis/ProfileSummaryInfo.cpp

 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.
-  // 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,
                                   BlockFrequencyInfo *BFI) {
   auto Count = BFI->getBlockProfileCount(B);
   return Count && isColdCount(*Count);
 }
 

unittests/Analysis/ProfileSummaryInfoTest.cpp

TEST_F(ProfileSummaryInfoTest, InstrProf) {
   EXPECT_TRUE(PSI.isHotBB(BB3, &BFI));
 
   CallSite CS1(BB1->getFirstNonPHI());
   auto *CI2 = BB2->getFirstNonPHI();
   CallSite CS2(CI2);
 
   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) {
   auto M = makeLLVMModule("SampleProfile");
   Function *F = M->getFunction("f");
   ProfileSummaryInfo PSI = buildPSI(M.get());
 
   BasicBlock &BB0 = F->getEntryBlock();