[llvm] [LoopIdiom] Select llvm.experimental.memset.pattern intrinsic rather than memset_pattern16 libcall (PR #126736)

[Craig Topper via llvm-commits]

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@@ -1064,53 +1073,95 @@ bool LoopIdiomRecognize::processLoopStridedStore(
     return Changed;
 
   // Okay, everything looks good, insert the memset.
+  // MemsetArg is the number of bytes for the memset libcall, and the number
+  // of pattern repetitions if the memset.pattern intrinsic is being used.
+  Value *MemsetArg;
+  std::optional<int64_t> BytesWritten = std::nullopt;
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topperc wrote:

Do we need `= std::nullopt`?

https://github.com/llvm/llvm-project/pull/126736