[llvm] [DAG] computeKnownFPClass - add ISD::EXTRACT_VECTOR_ELT handling (PR #190307)

[Simon Pilgrim via llvm-commits]

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@@ -16060,6 +16056,14 @@ SDValue DAGCombiner::visitIS_FPCLASS(SDNode *N) {
 
   KnownFPClass Known = DAG.computeKnownFPClass(Src, Mask);
 
+  // All possible classes ruled out: result is always false.
+  if ((Mask & Known.KnownFPClasses) == fcNone)
+    return DAG.getBoolConstant(false, DL, VT, Src.getValueType());
+
+  // All possible classes are within the mask: result is always true.
+  if ((~Mask & Known.KnownFPClasses) == fcNone)
+    return DAG.getBoolConstant(true, DL, VT, Src.getValueType());
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RKSimon wrote:

drop it - you shouldn't need it for ISD::EXTRACT_VECTOR_ELT handling

https://github.com/llvm/llvm-project/pull/190307