[AArch64] Fix assertion failure in getCastInstrCost

We should not call `getVectorElementType` on the result MVT from
`getTypeLegalizationCost` when we don't if the legal type is a
vector. This is the case when the type needs to be legalized
using scalarization.

Author: sdesmalen-arm

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -2785,7 +2785,7 @@ InstructionCost AArch64TTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
     std::pair<InstructionCost, MVT> LT =
         getTypeLegalizationCost(WiderTy.getTypeForEVT(Dst->getContext()));
     unsigned NumElements = AArch64::SVEBitsPerBlock /
-                           LT.second.getVectorElementType().getSizeInBits();
+                           LT.second.getScalarSizeInBits();
     return AdjustCost(
         LT.first *
         getCastInstrCost(

llvm/test/Analysis/CostModel/AArch64/no-sve-no-neon.ll

@@ -1,16 +1,15 @@
 ; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 2
-; RUN: opt < %s -passes="print<cost-model>" 2>&1 -disable-output | FileCheck %s
+; RUN: opt -mattr=-neon < %s -passes="print<cost-model>" 2>&1 -disable-output | FileCheck %s
+; RUN: opt -mattr=+sve,-neon < %s -passes="print<cost-model>" 2>&1 -disable-output | FileCheck %s
 
 target triple = "aarch64-unknown-linux-gnu"
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 
-define void @uitofp() #0 {
+define void @uitofp() {
 ; CHECK-LABEL: 'uitofp'
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 16 for instruction: %conv = uitofp <16 x i64> undef to <16 x float>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
   %conv = uitofp <16 x i64> undef to <16 x float>
   ret void
 }
-
-attributes #0 = { "target-features"="-neon" }