[llvm] Add target hook for automatic histogram vectorization (PR #128414)

[Graham Hunter via llvm-commits]

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@@ -310,6 +310,22 @@ class TargetTransformInfoImplBase {
     return false;
   }
 
+  bool isLegalForHistogramVectorization(const LoadInst *LI,
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huntergr-arm wrote:

I'm wondering if you could add the load and store to the parameters in IntrinsicCostAttributes when asking for the cost of a histogram intrinsic, and return Invalid if the target doesn't support it instead of introducing a new method.

I guess this is a fast way of rejecting something in a different address space though, without going through the rest of the analysis.

https://github.com/llvm/llvm-project/pull/128414