[LoopUtils] Saturate at INT_MAX when estimating TC (#129683)

getLoopEstimatedTripCount returns std::nullopt when the trip count would
overflow the return type, but since it is an estimate anyway, we might
as well saturate at UINT_MAX, improving results.

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index ec1692a..42c70d2 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -843,9 +843,9 @@ static std::optional<unsigned> getEstimatedTripCount(BranchInst *ExitingBranch,
   // edge exiting the loop, rounded to nearest.
   uint64_t ExitCount = llvm::divideNearest(LoopWeight, ExitWeight);
 
-  // When ExitCount + 1 would wrap in unsigned, return std::nullopt instead.
+  // When ExitCount + 1 would wrap in unsigned, saturate at UINT_MAX.
   if (ExitCount >= std::numeric_limits<unsigned>::max())
-    return std::nullopt;
+    return std::numeric_limits<unsigned>::max();
 
   // Estimated trip count is one plus estimated exit count.
   return ExitCount + 1;