[llvm] [AArch64][SVE] - Fix crash Possible incorrect use of EVT::getVectorNumElements(). (PR #218733)

[David Sherwood via llvm-commits]

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@@ -4712,7 +4712,7 @@ SDValue DAGCombiner::visitSUBSAT(SDNode *N) {
   // Narrow a vXiN USUBSAT to a smaller type when both operands are known
   // to fit in fewer bits. This allows targets with native narrow USUBSAT
   // (e.g. vpsubusb/vpsubusw) to avoid emulation with vpmaxu + vsub.
-  if (!IsSigned && VT.isVector() && VT.isSimple()) {
+  if (!IsSigned && VT.isFixedLengthVector() && VT.isSimple()) {
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david-arm wrote:

It's a shame this has to bail out for scalable vectors, but looking at the `computeKnownBits` call below it's unlikely to work I think.

https://github.com/llvm/llvm-project/pull/218733