[compiler-rt][builtins][FMV] Early exit in the Apple __init_cpu_features_resolver(). NFC

Author: jroelofs

compiler-rt/lib/builtins/cpu_model/aarch64/fmv/apple.inc

@@ -17,55 +17,56 @@ void __init_cpu_features_resolver(void) {
   // ELF platforms, where IFuncs are resolved serially at load time). This
   // function's effect on __aarch64_cpu_features must be idempotent.
 
-  if (!__atomic_load_n(&__aarch64_cpu_features.features, __ATOMIC_RELAXED)) {
-    uint64_t features = 0;
+  if (__atomic_load_n(&__aarch64_cpu_features.features, __ATOMIC_RELAXED))
+    return;
 
-    // https://developer.apple.com/documentation/kernel/1387446-sysctlbyname/determining_instruction_set_characteristics
-    static const struct {
-      const char *sysctl_name;
-      enum CPUFeatures feature;
-    } feature_checks[] = {
-        {"hw.optional.arm.FEAT_FlagM", FEAT_FLAGM},
-        {"hw.optional.arm.FEAT_FlagM2", FEAT_FLAGM2},
-        {"hw.optional.arm.FEAT_FHM", FEAT_FP16FML},
-        {"hw.optional.arm.FEAT_DotProd", FEAT_DOTPROD},
-        {"hw.optional.arm.FEAT_RDM", FEAT_RDM},
-        {"hw.optional.arm.FEAT_LSE", FEAT_LSE},
-        {"hw.optional.floatingpoint", FEAT_FP},
-        {"hw.optional.AdvSIMD", FEAT_SIMD},
-        {"hw.optional.armv8_crc32", FEAT_CRC},
-        {"hw.optional.arm.FEAT_SHA1", FEAT_SHA1},
-        {"hw.optional.arm.FEAT_SHA256", FEAT_SHA2},
-        {"hw.optional.arm.FEAT_SHA3", FEAT_SHA3},
-        {"hw.optional.arm.FEAT_AES", FEAT_AES},
-        {"hw.optional.arm.FEAT_PMULL", FEAT_PMULL},
-        {"hw.optional.arm.FEAT_FP16", FEAT_FP16},
-        {"hw.optional.arm.FEAT_DIT", FEAT_DIT},
-        {"hw.optional.arm.FEAT_DPB", FEAT_DPB},
-        {"hw.optional.arm.FEAT_DPB2", FEAT_DPB2},
-        {"hw.optional.arm.FEAT_JSCVT", FEAT_JSCVT},
-        {"hw.optional.arm.FEAT_FCMA", FEAT_FCMA},
-        {"hw.optional.arm.FEAT_LRCPC", FEAT_RCPC},
-        {"hw.optional.arm.FEAT_LRCPC2", FEAT_RCPC2},
-        {"hw.optional.arm.FEAT_FRINTTS", FEAT_FRINTTS},
-        {"hw.optional.arm.FEAT_I8MM", FEAT_I8MM},
-        {"hw.optional.arm.FEAT_BF16", FEAT_BF16},
-        {"hw.optional.arm.FEAT_SB", FEAT_SB},
-        {"hw.optional.arm.FEAT_SPECRES", FEAT_PREDRES},
-        {"hw.optional.arm.FEAT_SSBS", FEAT_SSBS2},
-        {"hw.optional.arm.FEAT_BTI", FEAT_BTI},
-    };
+  uint64_t features = 0;
 
-    for (size_t I = 0, E = sizeof(feature_checks) / sizeof(feature_checks[0]);
-         I != E; ++I)
-      if (isKnownAndSupported(feature_checks[I].sysctl_name))
-        features |= (1ULL << feature_checks[I].feature);
+  // https://developer.apple.com/documentation/kernel/1387446-sysctlbyname/determining_instruction_set_characteristics
+  static const struct {
+    const char *sysctl_name;
+    enum CPUFeatures feature;
+  } feature_checks[] = {
+      {"hw.optional.arm.FEAT_FlagM", FEAT_FLAGM},
+      {"hw.optional.arm.FEAT_FlagM2", FEAT_FLAGM2},
+      {"hw.optional.arm.FEAT_FHM", FEAT_FP16FML},
+      {"hw.optional.arm.FEAT_DotProd", FEAT_DOTPROD},
+      {"hw.optional.arm.FEAT_RDM", FEAT_RDM},
+      {"hw.optional.arm.FEAT_LSE", FEAT_LSE},
+      {"hw.optional.floatingpoint", FEAT_FP},
+      {"hw.optional.AdvSIMD", FEAT_SIMD},
+      {"hw.optional.armv8_crc32", FEAT_CRC},
+      {"hw.optional.arm.FEAT_SHA1", FEAT_SHA1},
+      {"hw.optional.arm.FEAT_SHA256", FEAT_SHA2},
+      {"hw.optional.arm.FEAT_SHA3", FEAT_SHA3},
+      {"hw.optional.arm.FEAT_AES", FEAT_AES},
+      {"hw.optional.arm.FEAT_PMULL", FEAT_PMULL},
+      {"hw.optional.arm.FEAT_FP16", FEAT_FP16},
+      {"hw.optional.arm.FEAT_DIT", FEAT_DIT},
+      {"hw.optional.arm.FEAT_DPB", FEAT_DPB},
+      {"hw.optional.arm.FEAT_DPB2", FEAT_DPB2},
+      {"hw.optional.arm.FEAT_JSCVT", FEAT_JSCVT},
+      {"hw.optional.arm.FEAT_FCMA", FEAT_FCMA},
+      {"hw.optional.arm.FEAT_LRCPC", FEAT_RCPC},
+      {"hw.optional.arm.FEAT_LRCPC2", FEAT_RCPC2},
+      {"hw.optional.arm.FEAT_FRINTTS", FEAT_FRINTTS},
+      {"hw.optional.arm.FEAT_I8MM", FEAT_I8MM},
+      {"hw.optional.arm.FEAT_BF16", FEAT_BF16},
+      {"hw.optional.arm.FEAT_SB", FEAT_SB},
+      {"hw.optional.arm.FEAT_SPECRES", FEAT_PREDRES},
+      {"hw.optional.arm.FEAT_SSBS", FEAT_SSBS2},
+      {"hw.optional.arm.FEAT_BTI", FEAT_BTI},
+  };
 
-    features |= (1ULL << FEAT_INIT);
+  for (size_t I = 0, E = sizeof(feature_checks) / sizeof(feature_checks[0]);
+        I != E; ++I)
+    if (isKnownAndSupported(feature_checks[I].sysctl_name))
+      features |= (1ULL << feature_checks[I].feature);
 
-    __atomic_store(&__aarch64_cpu_features.features, &features,
-                   __ATOMIC_RELAXED);
-  }
+  features |= (1ULL << FEAT_INIT);
+
+  __atomic_store(&__aarch64_cpu_features.features, &features,
+                  __ATOMIC_RELAXED);
 }
 
 #endif // TARGET_OS_OSX || TARGET_OS_IPHONE