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

[Matt Arsenault via llvm-commits]

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@@ -1154,7 +1154,7 @@ bool LoopIdiomRecognize::processLoopStridedStore(
                                               PatternValue, ".memset_pattern");
       GV->setUnnamedAddr(
           GlobalValue::UnnamedAddr::Global); // Ok to merge these.
-      GV->setAlignment(Align(PatternArgTy->getPrimitiveSizeInBits()));
+      GV->setAlignment(Align(PatternArgTy->getPrimitiveSizeInBits() / 8));
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arsenm wrote:

Just above you already queried the getTypeSizeInBits for PatternArgTy, avoid repeating it? Every getPrimitiveSizeInBits makes me nervous 

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