[llvm] [AArch64][SME2] Extend SMEABIPass to handle functions with new ZT0 state (PR #78848)

[Sander de Smalen via llvm-commits]

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@@ -153,3 +153,118 @@ define void @zt0_in_caller_zt0_new_callee() "aarch64_in_zt0" nounwind {
   call void @callee() "aarch64_new_zt0";
   ret void;
 }
+
+;
+; New-ZA Caller
+;
+
+; Expect commit of lazy-save if ZA is dormant
+; Expect smstart ZA & clear ZT0
+; Before return, expect smstop ZA
+define void @zt0_new_caller() "aarch64_new_zt0" nounwind {
+; CHECK-LABEL: zt0_new_caller:
+; CHECK:       // %bb.0: // %prelude
+; CHECK-NEXT:    sub sp, sp, #80
+; CHECK-NEXT:    str x30, [sp, #64] // 8-byte Folded Spill
+; CHECK-NEXT:    mrs x8, TPIDR2_EL0
+; CHECK-NEXT:    cbz x8, .LBB6_2
+; CHECK-NEXT:  // %bb.1: // %save.za
+; CHECK-NEXT:    mov x8, sp
+; CHECK-NEXT:    str zt0, [x8]
+; CHECK-NEXT:    bl __arm_tpidr2_save
----------------
sdesmalen-arm wrote:

strictly speaking we could remove the spill/fill of ZT0 here, because ZT0 is overwritten below by the `zero { zt0 }`, but I guess that's an optimisation for a future patch.

https://github.com/llvm/llvm-project/pull/78848