Avoid BlockFrequency overflow problems (#66280)

Multiplying raw block frequency with an integer carries a high risk
of overflow.

- Add `BlockFrequency::mul` return an std::optional with the product
  or `nullopt` to indicate an overflow.
- Fix two instances where overflow was likely.

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index f07fc4f..faee623 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -198,7 +198,7 @@ static cl::opt<bool> BBSectionsGuidedSectionPrefix(
              "impacted, i.e., their prefixes will be decided by FDO/sampleFDO "
              "profiles."));
 
-static cl::opt<unsigned> FreqRatioToSkipMerge(
+static cl::opt<uint64_t> FreqRatioToSkipMerge(
     "cgp-freq-ratio-to-skip-merge", cl::Hidden, cl::init(2),
     cl::desc("Skip merging empty blocks if (frequency of empty block) / "
              "(frequency of destination block) is greater than this ratio"));
@@ -986,8 +986,8 @@ bool CodeGenPrepare::isMergingEmptyBlockProfitable(BasicBlock *BB,
         DestBB == findDestBlockOfMergeableEmptyBlock(SameValueBB))
       BBFreq += BFI->getBlockFreq(SameValueBB);
 
-  return PredFreq.getFrequency() <=
-         BBFreq.getFrequency() * FreqRatioToSkipMerge;
+  std::optional<BlockFrequency> Limit = BBFreq.mul(FreqRatioToSkipMerge);
+  return !Limit || PredFreq <= *Limit;
 }
 
 /// Return true if we can merge BB into DestBB if there is a single