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

[Sam Tebbs via llvm-commits]

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@@ -1142,6 +1146,30 @@ bool AArch64ExpandPseudo::expandMultiVecPseudo(
   return true;
 }
 
+bool AArch64ExpandPseudo::expandFormTuplePseudo(
+    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
+    MachineBasicBlock::iterator &NextMBBI, unsigned Size) {
+  assert(Size == 2 || Size == 4 && "Invalid Tuple Size");
+  MachineInstr &MI = *MBBI;
+  Register ReturnTuple = MI.getOperand(0).getReg();
+
+  const TargetRegisterInfo *TRI =
+      MBB.getParent()->getSubtarget().getRegisterInfo();
+  for (unsigned i = 0; i < Size; i++) {
+    Register FormTupleOpReg = MI.getOperand(i + 1).getReg();
+    Register ReturnTupleSubReg =
+        TRI->getSubReg(ReturnTuple, AArch64::zsub0 + i);
+    if (FormTupleOpReg != ReturnTupleSubReg)
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SamTebbs33 wrote:

I think a comment about why this check is necessary would be good.

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