[llvm] [ExpandVectorPredication] Expand vp_merge and vp_select in expandPredication. (PR #157777)

[Craig Topper via llvm-commits]

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@@ -581,6 +581,14 @@ bool CachingVPExpander::expandPredication(VPIntrinsic &VPI) {
     replaceOperation(*NewNegOp, VPI);
     return NewNegOp;
   }
+  case Intrinsic::vp_select:
+  case Intrinsic::vp_merge: {
+    assert(maySpeculateLanes(VPI) || VPI.canIgnoreVectorLengthParam());
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topperc wrote:

I think the code here https://github.com/llvm/llvm-project/blob/27719745e3b0f7bed738a67498e751ca6d45bcdd/llvm/lib/CodeGen/ExpandVectorPredication.cpp#L642 forces the EVLStrategy to Convert if the intrinsic is to be converted.  That causes this code https://github.com/llvm/llvm-project/blob/27719745e3b0f7bed738a67498e751ca6d45bcdd/llvm/lib/CodeGen/ExpandVectorPredication.cpp#L679 to fold the EVL into the mask.

https://github.com/llvm/llvm-project/pull/157777