[compiler-rt] [AArch64][SME] Rewrite __arm_get_current_vg to preserve required registers (PR #100143)

[Sander de Smalen via llvm-commits]

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@@ -180,6 +184,48 @@ DEFINE_COMPILERRT_OUTLINE_FUNCTION_UNMANGLED(__arm_za_disable)
   ret
 END_COMPILERRT_OUTLINE_FUNCTION(__arm_za_disable)
 
+DEFINE_COMPILERRT_OUTLINE_FUNCTION_UNMANGLED(__arm_get_current_vg)
+  .variant_pcs __arm_get_current_vg
+  BTI_C
+  mov x0, xzr
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sdesmalen-arm wrote:

Is this necessary? I'd expect it to be overwritten by the call to `__arm_sme_state`.

https://github.com/llvm/llvm-project/pull/100143