[llvm] [PGO] Fix zeroed estimated trip count (PR #167792)

[Joel E. Denny via llvm-commits]

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@@ -912,12 +912,14 @@ llvm::getLoopEstimatedTripCount(Loop *L,
   }
 
   // Return the estimated trip count from metadata unless the metadata is
-  // missing or has no value.
+  // missing or has no value.  Return std::nullopt if it's zero.
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jdenny-ornl wrote:

Done.  Thanks for the review.

https://github.com/llvm/llvm-project/pull/167792