[BasicTTI] Account for vector of pointers in getMemoryOpCost

[reames]

Summary

By using getPrimitiveSizeInBits, we were getting 0 for every pointer type. This code is trying to account for the cost of truncating a store or extending a load to convert from the source vector element type to the legal vector element type.

I'd originally seen this as a crash when trying to scalarize a <vscale x 1 x ptr> type coming from the vectorizer. Here's a minimum reproducer to exercise the code in question.

void e(int *argv[], int *p) {
  for (int i = 0; i < 1024; i++)
    argv[i] = p;
}

This was checked in as the splat_ptr test in 2cf320d. After bbf3fd, this no longer crashes since we correctly return invalid if the extending load/truncating store isn't legal.

[reames]

Rebase over newly added tests - after thinking about this a bit more, I realized this was exerciseable through CostModel.

[craig.topper]

LGTM

llvm/include/llvm/CodeGen/BasicTTIImpl.h

InstructionCost getMemoryOpCost(unsigned Opcode, Type *Src,
     InstructionCost Cost = LT.first;
     if (CostKind != TTI::TCK_RecipThroughput)
       return Cost;
 
     if (Src->isVectorTy() &&
         // In practice it's not currently possible to have a change in lane
         // length for extending loads or truncating stores so both types should
         // have the same scalable property.
-        TypeSize::isKnownLT(Src->getPrimitiveSizeInBits(),
+        TypeSize::isKnownLT(DL.getTypeStoreSizeInBits(Src),
                             LT.second.getSizeInBits())) {
       // This is a vector load that legalizes to a larger type than the vector
       // itself. Unless the corresponding extending load or truncating store is
       // legal, then this will scalarize.
       TargetLowering::LegalizeAction LA = TargetLowering::Expand;
       EVT MemVT = getTLI()->getValueType(DL, Src);
       if (Opcode == Instruction::Store)
         LA = getTLI()->getTruncStoreAction(LT.second, MemVT);