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

[Simon Pilgrim via llvm-commits]

================
@@ -8379,12 +8398,12 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     if (N1.isUndef() || N2.isUndef())
       return getUNDEF(VT);
 
-    // EXTRACT_VECTOR_ELT of out-of-bounds element is an UNDEF for fixed length
+    // EXTRACT_VECTOR_ELT of out-of-bounds element is an POISON for fixed length
     // vectors. For scalable vectors we will provide appropriate support for
     // dealing with arbitrary indices.
     if (N2C && N1.getValueType().isFixedLengthVector() &&
         N2C->getAPIntValue().uge(N1.getValueType().getVectorNumElements()))
-      return getUNDEF(VT);
+      return getPOISON(VT);
----------------
RKSimon wrote:

this needs pulling out into its own PR

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