[llvm] clastb representation in existing IR, and AArch64 codegen (PR #112738)

[Sam Tebbs via llvm-commits]

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@@ -490,6 +490,11 @@ class TargetLoweringBase {
     return true;
   }
 
+  virtual bool
+  shouldExpandVectorExtractLastActive(const IntrinsicInst *I) const {
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SamTebbs33 wrote:

I think we;ll want a doc comment here.

https://github.com/llvm/llvm-project/pull/112738