Clean up usages of asserting vector getters in Type

[ctetreau]

Summary

Remove usages of asserting vector getters in Type in preparation for the
VectorType refactor. The existence of these functions complicates the
refactor while adding little value.

[ctetreau]

Update to mention that this is NFC

[ctetreau]

rebase, mention powerpc in commit message

[efriedma]

LGTM

llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp

int PPCTTIImpl::getMemoryOpCost(unsigned Opcode, Type *Src,
   // Add the cost of each scalar load or store.
   assert(Alignment);
   Cost += LT.first * ((SrcBytes / Alignment->value()) - 1);
 
   // For a vector type, there is also scalarization overhead (only for
   // stores, loads are expanded using the vector-load + permutation sequence,
   // which is much less expensive).
   if (Src->isVectorTy() && Opcode == Instruction::Store)
-    for (int i = 0, e = Src->getVectorNumElements(); i < e; ++i)
+    for (int i = 0, e = cast<VectorType>(Src)->getNumElements(); i < e; ++i)
       Cost += getVectorInstrCost(Instruction::ExtractElement, Src, i);
 
   return Cost;
 }
 
 int PPCTTIImpl::getInterleavedMemoryOpCost(unsigned Opcode, Type *VecTy,
                                            unsigned Factor,
                                            ArrayRef<unsigned> Indices,