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

[Sander de Smalen via llvm-commits]

================
@@ -8666,6 +8718,30 @@ void AArch64TargetLowering::AdjustInstrPostInstrSelection(MachineInstr &MI,
     }
   }
 
+  if (MI.getOpcode() == AArch64::FORM_TRANSPOSED_REG_TUPLE_X2_PSEUDO ||
+      MI.getOpcode() == AArch64::FORM_TRANSPOSED_REG_TUPLE_X4_PSEUDO) {
+    // If input values to the FORM_TRANSPOSED_REG_TUPLE pseudo aren't copies
+    // from a StridedOrContiguous class, fall back on REG_SEQUENCE node.
+    if (shouldUseFormStridedPseudo(MI))
+      return;
+
+    static const unsigned SubRegs[] = {AArch64::zsub0, AArch64::zsub1,
+                                       AArch64::zsub2, AArch64::zsub3};
+
+    const TargetInstrInfo *TII = Subtarget->getInstrInfo();
+    MachineInstrBuilder MIB = BuildMI(*MI.getParent(), MI, MI.getDebugLoc(),
+                                      TII->get(TargetOpcode::REG_SEQUENCE),
+                                      MI.getOperand(0).getReg());
+
+    for (unsigned I = 1; I < MI.getNumOperands(); ++I) {
+      MIB.add(MI.getOperand(I));
+      MIB.addImm(SubRegs[I - 1]);
----------------
sdesmalen-arm wrote:

nit:
```suggestion
      MIB.addImm(AArch64::zsub0 + (I-1));
```
Then you can remove `SubRegs[]`.

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