[compiler-rt] [AArch64][compiler-rt] Add a function returning the current vector length (PR #92921)

[Kerry McLaughlin via llvm-commits]

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@@ -50,3 +52,35 @@ __attribute__((constructor(90)))
 static void init_aarch64_has_sme(void) {
   __aarch64_has_sme_and_tpidr2_el0 = has_sme();
 }
+
+#if __GNUC__ >= 9
+#pragma GCC diagnostic ignored "-Wprio-ctor-dtor"
+#endif
+__attribute__((constructor(90))) static void get_aarch64_cpu_features(void) {
+  if (!__get_aarch64_features())
+    __init_cpu_features();
+}
+
+struct SME_STATE {
+  long PSTATE;
+  long TPIDR2_EL0;
+};
+
+extern struct SME_STATE __arm_sme_state(void) __arm_streaming_compatible;
+
+__attribute__((target("sve"))) long
+__arm_get_current_vg(void) __arm_streaming_compatible {
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kmclaughlin-arm wrote:

I've split this into a separate file and replaced the use of `has_sme()` with `__aarch64_has_sme_and_tpidr2_el0`.

https://github.com/llvm/llvm-project/pull/92921