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

[Dinar Temirbulatov via llvm-commits]

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@@ -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)
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dtemirbulatov wrote:

Is it safe to override ISD::DYNAMIC_STACKALLOC lowering here? I noticed that Windows implementation might be different.

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