[llvm] [DAGCombiner] Add support for scalarising extracts of a vector setcc (PR #116031)

[David Sherwood via llvm-commits]

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@@ -3334,6 +3334,10 @@ class TargetLoweringBase {
     return false;
   }
 
+  /// Try to convert an extract element of a vector setcc operation into an
+  /// extract element followed by a scalar operation.
+  virtual bool shouldScalarizeSetCC(SDValue VecOp) const { return false; }
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david-arm wrote:

I could just reuse the existing `shouldScalarizeBinOp` hook, but the setcc op feels like a special case because the result type is often different to the input (e.g. v4i1 output, v4i32 input, etc.) and may set condition registers.

https://github.com/llvm/llvm-project/pull/116031