[llvm] [RISCV][GlobalISel] Legalize Scalable Vector Loads and Stores (PR #84965)

[Michael Maitland via llvm-commits]

================
@@ -651,6 +687,62 @@ bool RISCVLegalizerInfo::legalizeExt(MachineInstr &MI,
   return true;
 }
 
+bool RISCVLegalizerInfo::legalizeLoadStore(MachineInstr &MI,
+                                           LegalizerHelper &Helper,
+                                           MachineIRBuilder &MIB) const {
+  MachineRegisterInfo &MRI = *MIB.getMRI();
+  MachineFunction *MF = MI.getMF();
+  const DataLayout &DL = MIB.getDataLayout();
+  LLVMContext &Ctx = MF->getFunction().getContext();
+
+  Register DstReg = MI.getOperand(0).getReg();
+  Register PtrReg = MI.getOperand(1).getReg();
+  LLT DataTy = MRI.getType(DstReg);
+  if (!DataTy.isVector())
+    return false;
+
+  if (!(STI.hasVInstructions() &&
+        (DataTy.getScalarSizeInBits() != 64 || STI.hasVInstructionsI64()) &&
+        (DataTy.getElementCount().getKnownMinValue() != 1 ||
+         STI.getELen() == 64)))
+    return false;
+
+  if (!MI.hasOneMemOperand())
+    return false;
+
+  MachineMemOperand *MMO = *MI.memoperands_begin();
+  Align Alignment = MMO->getAlign();
+
+  const auto *TLI = STI.getTargetLowering();
+  EVT VT = EVT::getEVT(getTypeForLLT(DataTy, Ctx));
+
+  if (TLI->allowsMemoryAccessForAlignment(Ctx, DL, VT, *MMO))
+    return true;
+
+  unsigned EltSizeBits = DataTy.getScalarSizeInBits();
+  assert((EltSizeBits == 16 || EltSizeBits == 32 || EltSizeBits == 64) &&
+         "Unexpected unaligned RVV load type");
+
+  // Calculate the new vector type with i8 elements
+  unsigned NumElements =
+      DataTy.getElementCount().getKnownMinValue() * (EltSizeBits / 8);
+  LLT NewDataTy = LLT::scalable_vector(NumElements, 8);
+
+  MachinePointerInfo PI = MMO->getPointerInfo();
+  MachineMemOperand *NewMMO =
+      MF->getMachineMemOperand(PI, MMO->getFlags(), NewDataTy, Alignment);
+
+  if (isa<GLoad>(MI)) {
+    Helper.bitcast(MI, 0, NewDataTy);
+  } else {
+    assert(isa<GStore>(MI) && "Machine instructions must be Load/Store.");
----------------
michaelmaitland wrote:

Can we assert at the top of the function that this is a load or store instead?

https://github.com/llvm/llvm-project/pull/84965