[GlobalISel] (fix) Use pointer type size for offset constant when lowering stores

[gargaroff]

Summary

Commit 9965b12fd1b was supposed to change the offset constant when lowering load/stores, but only introduced this change for loads. This patch adds the same fix for stores.

[gargaroff]

Ping

[gargaroff]

Thanks. Would you merge this for me?

[arsenm]

dc141af7553871b94f0d7cb4b1f2096578a923be

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

case TargetOpcode::G_STORE: {
     // Obtain the smaller value by shifting away the larger value.
     uint64_t LargeSplitSize = PowerOf2Floor(SrcTy.getSizeInBits());
     uint64_t SmallSplitSize = SrcTy.getSizeInBits() - LargeSplitSize;
     auto ShiftAmt = MIRBuilder.buildConstant(ExtendTy, LargeSplitSize);
     auto SmallVal = MIRBuilder.buildLShr(ExtendTy, ExtVal, ShiftAmt);
 
     // Generate the PtrAdd and truncating stores.
     LLT PtrTy = MRI.getType(PtrReg);
-    auto OffsetCst =
-        MIRBuilder.buildConstant(LLT::scalar(64), LargeSplitSize / 8);
+    auto OffsetCst = MIRBuilder.buildConstant(
+            LLT::scalar(PtrTy.getSizeInBits()), LargeSplitSize / 8);
     Register PtrAddReg = MRI.createGenericVirtualRegister(PtrTy);
     auto SmallPtr =
         MIRBuilder.buildPtrAdd(PtrAddReg, PtrReg, OffsetCst.getReg(0));
 
     MachineFunction &MF = MIRBuilder.getMF();
     MachineMemOperand *LargeMMO =
         MF.getMachineMemOperand(&MMO, 0, LargeSplitSize / 8);
     MachineMemOperand *SmallMMO =