[llvm] [LoopVectorizer] Add support for partial reductions (PR #92418)

[via llvm-commits]

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@@ -512,6 +512,16 @@ class VectorType : public Type {
                            EltCnt.divideCoefficientBy(2));
   }
 
+  /// This static method returns a VectorType with quarter as many elements as the
+  /// input type and the same element type.
+  static VectorType *getQuarterElementsVectorType(VectorType *VTy) {
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NickGuy-Arm wrote:

I've removed the restriction of only being 4x, opting instead for any vector type being valid and having the restrictions be defined by whatever emits the intrinsic (In this case, the Loop Vectorizer)

https://github.com/llvm/llvm-project/pull/92418