[llvm] [AArch64][SME2] Add FORM_STRIDED_TUPLE pseudo nodes (PR #116399)

[Sander de Smalen via llvm-commits]

================
@@ -8641,6 +8641,57 @@ static bool checkZExtBool(SDValue Arg, const SelectionDAG &DAG) {
   return ZExtBool;
 }
 
+// The FORM_TRANSPOSED_REG_TUPLE pseudo should only be used if the
+// input operands are copy nodes where the source register is in a
+// StridedOrContiguous class. For example:
+//
+//   %3:zpr2stridedorcontiguous = LD1B_2Z_IMM_PSEUDO ..
+//   %4:zpr = COPY %3.zsub1:zpr2stridedorcontiguous
+//   %5:zpr = COPY %3.zsub0:zpr2stridedorcontiguous
+//   %6:zpr2stridedorcontiguous = LD1B_2Z_PSEUDO ..
+//   %7:zpr = COPY %6.zsub1:zpr2stridedorcontiguous
+//   %8:zpr = COPY %6.zsub0:zpr2stridedorcontiguous
+//   %9:zpr2mul2 = FORM_TRANSPOSED_REG_TUPLE_X2_PSEUDO %5:zpr, %8:zpr
+//
+bool shouldUseFormStridedPseudo(MachineInstr &MI) {
+  MachineRegisterInfo &MRI = MI.getMF()->getRegInfo();
+
+  MCRegister SubReg = MCRegister::NoRegister;
+  for (unsigned I = 1; I < MI.getNumOperands(); ++I) {
+    MachineOperand &MO = MI.getOperand(I);
+    assert(MO.isReg() && "Unexpected operand to FORM_TRANSPOSED_REG_TUPLE");
+
+    MachineOperand *Def = MRI.getOneDef(MO.getReg());
+    if (!Def || !Def->getParent()->isCopy())
+      return false;
+
+    const MachineOperand &CpySrc = Def->getParent()->getOperand(1);
----------------
sdesmalen-arm wrote:

nit: 
```suggestion
    const MachineOperand &CopySrc = Def->getParent()->getOperand(1);
```
(to be consistent with the 'o' in Copy you've added to the other variable name)

https://github.com/llvm/llvm-project/pull/116399