[VPlan] Handle invariant GEPs in isUniformAfterVectorization.

This fixes a crash caused by legal treating a scalable GEP as invariant,
but isUniformAfterVectorization does not handle GEPs.

Partially fixes #60831.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D144434

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -2979,6 +2979,8 @@ inline bool isUniformAfterVectorization(VPValue *VPV) {
   assert(Def && "Must have definition for value defined inside vector region");
   if (auto Rep = dyn_cast<VPReplicateRecipe>(Def))
     return Rep->isUniform();
+  if (auto *GEP = dyn_cast<VPWidenGEPRecipe>(Def))
+    return all_of(GEP->operands(), isUniformAfterVectorization);
   return false;
 }
 } // end namespace vputils