[llvm] [AArch64] Lower partial add reduction to udot or svdot (PR #101010)

[Sam Tebbs via llvm-commits]

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@@ -3533,6 +3533,36 @@ AArch64TTIImpl::getCostOfKeepingLiveOverCall(ArrayRef<Type *> Tys) {
   return Cost;
 }
 
+bool AArch64TTIImpl::isPartialReductionSupported(
+    const Instruction *ReductionInstr, Type *InputType, unsigned ScaleFactor,
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SamTebbs33 wrote:

It's the scaling difference between the element size of the inputs and the size of the resulting scalar from the entire reduction. In the tests you'll see that the input types are extended and the resulting scalar is 4 times the size, which mirrors how the dot product instructions work.

https://github.com/llvm/llvm-project/pull/101010