[WIP] support arm_neon_optional flag in blink.

Source/wtf/CPU.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007-2009 Torch Mobile, Inc.
  * Copyright (C) 2010, 2011 Research In Motion Limited. All rights reserved.
  * Copyright (C) 2013 Samsung Electronics. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 137 matching lines @@
 #  if defined(thumb2) || defined(__thumb2__) \
     || ((defined(__thumb) || defined(__thumb__)) && WTF_THUMB_ARCH_VERSION == 4)
 #    define WTF_CPU_ARM_THUMB2 1
 #  elif WTF_ARM_ARCH_AT_LEAST(4)
 #    define WTF_CPU_ARM_THUMB2 0
 #  else
 #    error "Unsupported ARM architecture"
 #  endif
 #endif /* !defined(WTF_CPU_ARM_THUMB2) */
 
-#if defined(__ARM_NEON__) && !defined(WTF_CPU_ARM_NEON)
-#define WTF_CPU_ARM_NEON 1
+// The isSupportedNEON() function returns true if the target device
+// is higher than ARMv7-A and supports Neon instructions.
+// In OPTIONAL mode, this actually probes the CPU at runtime (and caches the result).
+#if CPU(ARM_NEON)
+static inline bool isSupportedNEON(void) { return true; }
+#elif CPU(ARM_NEON_OPTIONAL)
+extern bool isSupportedNEON(void) WTF_PURE_FUNCTION;
+#else
+static inline bool isSupportedNEON(void) { return false; }
 #endif
 
-#if CPU(ARM_NEON) && (!COMPILER(GCC) || GCC_VERSION_AT_LEAST(4, 7, 0))
-// All NEON intrinsics usage can be disabled by this macro.
-#define HAVE_ARM_NEON_INTRINSICS 1
+// Helper macro
+#define WTF_CPU_ARM_HAS_NEON() isSupportedNEON()
+
+// Use WTF_CPU_ARM_NEON_WRAP(symbol) to map 'symbol' to a NEON-specific symbol
+// when applicable. This will transform 'symbol' differently depending on
+// the current NEON configuration, i.e.:
+//
+//    NONE                             -> 'symbol'
+//    WTF_CPU_ARM_NEON                 -> 'symbolNEON'
+//    WTF_CPU_ARM_NEON_OPTIONAL        -> 'symbol' or 'symbolNEON' depending on runtime check.
+#if CPU(ARM_NEON)
+#  define WTF_CPU_ARM_NEON_WRAP(x) (x ## NEON)
+#elif CPU(ARM_NEON_OPTIONAL)
+#  define WTF_CPU_ARM_NEON_WRAP(x) (WTF_CPU_ARM_HAS_NEON() ? x ## NEON : x)
+#else
+#  define WTF_CPU_ARM_NEON_WRAP(x) (x)
 #endif
 
 #if defined(__ARM_ARCH_7S__)
 #define WTF_CPU_APPLE_ARMV7S 1
 #endif
 
 #if !defined(WTF_CPU_64BIT)
 #define WTF_CPU_32BIT 1
 #endif
 
 #endif /* ARM */
 
 /* CPU(ARM64) - AArch64 64-bit */
 #if defined(__aarch64__)
 #define WTF_CPU_ARM64 1
 #define WTF_CPU_64BIT 1
 #endif
 
 #endif /* WTF_CPU_h */