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

[Sam Tebbs via llvm-commits]

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@@ -1121,6 +1121,43 @@ bool AArch64ExpandPseudo::expandMI(MachineBasicBlock &MBB,
   default:
     break;
 
+  case AArch64::STORETPIDR2: {
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SamTebbs33 wrote:

We had an offline discussion and decided that the deallocation node can be made in the future if we find a case where the function epilogue doesn't deallocate the za buffer. We'll also pass the frame index to `ExpandZABuffer` along with the allocation size so both are in the DAG and can be optimised.

Since any time the lazy save buffer is used it will require the frame index, I will also investigate if the uses of the frame index can be queried to know if the buffer is required, rather than doing usage tracking in `TPIDR2Obj`.

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