[llvm] [LoopIdiomRecognize] Enable clmul optimization for CRC loops (PR #203405)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -669,6 +669,18 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
            TLI->isOperationLegalOrCustom(ISD::FSQRT, VT);
   }
 
+  bool haveFastClmul(IntegerType *Ty) const override {
+    // FIXME: clmul should really be Promote for any bitwidth under the largest
+    // legal bitwidth for clmul. This is a hack to get around that shortcoming.
+    if (auto *PromoteTy = dyn_cast_if_present<IntegerType>(
+            DL.getSmallestLegalIntType(Ty->getContext(), Ty->getBitWidth())))
----------------
artagnon wrote:

Hm, I suppose getLargestLegalIntType gives you worse results?

https://github.com/llvm/llvm-project/pull/203405