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

[Philip Reames via llvm-commits]

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@@ -1083,53 +1092,92 @@ 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;
+
+  if (PatternValue && (HasMemsetPattern || ForceMemsetPatternIntrinsic)) {
+    const SCEV *TripCountS =
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preames wrote:

There's a bunch of complexity in this section of the change that I'm not getting.  Since we need the NumBytes (in the original code) for the AAInfo, why not just leave that alone?  Isn't count (for memset.pattern intrinsic)  just the trip count of the loop by definition?

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