[SVE] Remove calls to getBitWidth from AArch64

[efriedma]

LGTM

[ctetreau]

rebase

[ctetreau]

change some misleading names

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

bool AArch64TargetLowering::isExtFreeImpl(const Instruction *Ext) const {
   }
   return true;
 }
 
 /// Check if both Op1 and Op2 are shufflevector extracts of either the lower
 /// or upper half of the vector elements.
 static bool areExtractShuffleVectors(Value *Op1, Value *Op2) {
   auto areTypesHalfed = [](Value *FullV, Value *HalfV) {
-    auto *FullVT = cast<VectorType>(FullV->getType());
-    auto *HalfVT = cast<VectorType>(HalfV->getType());
-    return FullVT->getBitWidth() == 2 * HalfVT->getBitWidth();
+    auto *FullVT = FullV->getType();
+    auto *HalfVT = HalfV->getType();
+    return FullVT->getPrimitiveSizeInBits().getFixedSize() ==
+           2 * HalfVT->getPrimitiveSizeInBits().getFixedSize();
   };
 
   auto extractHalf = [](Value *FullV, Value *HalfV) {
     auto *FullVT = cast<VectorType>(FullV->getType());
     auto *HalfVT = cast<VectorType>(HalfV->getType());
     return FullVT->getNumElements() == 2 * HalfVT->getNumElements();
   };