[compiler-rt] [Compiler-rt] Add AArch64 routines for __arm_agnostic("sme_za_state") (PR #120059)

[Paul Walker via llvm-commits]

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@@ -204,6 +206,163 @@ DEFINE_COMPILERRT_FUNCTION(__arm_get_current_vg)
   ret
 END_COMPILERRT_FUNCTION(__arm_get_current_vg)
 
+DEFINE_COMPILERRT_FUNCTION(__arm_sme_state_size)
+  .variant_pcs __arm_sme_state_size
+  BTI_C
+
+  // Test if SME is available and ZA state is 'active'.
+  adrp    x16, CPU_FEATS_SYMBOL
+  ldr     x16, [x16, CPU_FEATS_SYMBOL_OFFSET]
+  tbz     x16, #FEAT_SME_BIT, 0f
+  mrs     x16, SVCR
+  tbz     x16, #1, 0f
+  mrs     x16, TPIDR2_EL0
+  cbnz    x16, 0f
+
+  // Size = HAS_FEAT_SME2 ? 96 : 32
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paulwalker-arm wrote:

Whilst the specification wants to be vague about to the format of the buffer I think an implementation (i.e. these functions) should include some kind of header documentation that details the implemented layout.

https://github.com/llvm/llvm-project/pull/120059