[llvm] [DAG] Fixing the non-optimal code with the following: `select i1 %0, float 1.0, float 0.0`. (PR #107732)

[Simon Pilgrim via llvm-commits]

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@@ -24150,6 +24150,13 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) const {
                                           DAG.getBitcast(NVT, Op2)));
   }
 
+  // (select cc, 1.0, 0.0) -> (sint_to_fp (zext cc))
+  const ConstantFPSDNode *FPTV = dyn_cast<ConstantFPSDNode>(Op1);
+  const ConstantFPSDNode *FPFV = dyn_cast<ConstantFPSDNode>(Op2);
+  if (FPTV && FPFV && FPTV->isExactlyValue(1.0) && FPFV->isExactlyValue(0.0)) {
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RKSimon wrote:

This could either be added to combineSelectOfTwoConstants (which is currently integer-only), or we start a similar combineSelectOfTwoFPConstants

https://github.com/llvm/llvm-project/pull/107732