[llvm] [AArch64][SME] Remove unused ZA lazy-save (PR #81648)

[Sam Tebbs via llvm-commits]

================
@@ -2867,6 +2867,67 @@ AArch64TargetLowering::EmitZero(MachineInstr &MI, MachineBasicBlock *BB) const {
   return BB;
 }
 
+MachineBasicBlock *
+AArch64TargetLowering::EmitExpandZABuffer(MachineInstr &MI,
+                                          MachineBasicBlock *BB) const {
+  MachineFunction *MF = BB->getParent();
+  MachineFrameInfo &MFI = MF->getFrameInfo();
+  AArch64FunctionInfo *FuncInfo = MF->getInfo<AArch64FunctionInfo>();
+
+  std::optional<TPIDR2Object> TPIDR2 = FuncInfo->getTPIDR2Obj();
+  if (!TPIDR2)
+    llvm_unreachable("Cannot ExpandZABuffer without valid TPIDR2 object");
+
+  if (TPIDR2->Uses == 0) {
+    BB->remove_instr(&MI);
+    MFI.RemoveStackObject(TPIDR2->FrameIndex);
+    return BB;
+  }
+
+  const TargetInstrInfo *TII = Subtarget->getInstrInfo();
+  MachineRegisterInfo &MRI = MF->getRegInfo();
+
+  Register RDSVL = MRI.createVirtualRegister(&AArch64::GPR64RegClass);
+  BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(AArch64::RDSVLI_XI), RDSVL)
+      .addImm(1);
+
+  Register SP = MRI.createVirtualRegister(&AArch64::GPR64RegClass);
+  BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(TargetOpcode::COPY), SP)
+      .addReg(AArch64::SP);
+
+  Register MSub = MRI.createVirtualRegister(&AArch64::GPR64RegClass);
+  BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(AArch64::MSUBXrrr), MSub)
+      .addReg(RDSVL)
+      .addReg(RDSVL)
+      .addReg(SP);
+  BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(TargetOpcode::COPY), AArch64::SP)
+      .addReg(MSub);
+
+  unsigned TPIDR2Object = TPIDR2->FrameIndex;
+  MFI.CreateVariableSizedObject(Align(16), nullptr);
+
+  Register Zero32 = MRI.createVirtualRegister(&AArch64::GPR32RegClass);
+  MachineInstrBuilder Wzr =
+      BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(TargetOpcode::COPY), Zero32)
+          .addReg(AArch64::WZR);
+
+  BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(AArch64::STRXui))
----------------
SamTebbs33 wrote:

Good idea! Added now.

https://github.com/llvm/llvm-project/pull/81648