mesa: Replace a priori knowledge of gcc builtins with configure tests.

Presumbly this will let clang and other compilers use the built-ins as
well.

Notice two changes specifically:
   - in _mesa_next_pow_two_64(), always use __builtin_clzll and add a
     static assertion that this is safe.
   - in macros.h, remove the clang-specific definition since it should
     be able to detect __builtin_unreachable in configure.

Reviewed-by: Jason Ekstrand <[email protected]> [C bits]
Reviewed-by: Ian Romanick <[email protected]>

1 files changed, 3 insertions, 11 deletions

diff --git a/src/util/macros.h b/src/util/macros.h
index ee05e05a4a8..2e2f90f587c 100644
--- a/src/util/macros.h
+++ b/src/util/macros.h
@@ -33,12 +33,12 @@
 /**
  * __builtin_expect macros
  */
-#if !defined(__GNUC__)
+#if !defined(HAVE___BUILTIN_EXPECT)
 #  define __builtin_expect(x, y) (x)
 #endif
 
 #ifndef likely
-#  ifdef __GNUC__
+#  ifdef HAVE___BUILTIN_EXPECT
 #    define likely(x)   __builtin_expect(!!(x), 1)
 #    define unlikely(x) __builtin_expect(!!(x), 0)
 #  else
@@ -63,20 +63,12 @@
  * Unreachable macro. Useful for suppressing "control reaches end of non-void
  * function" warnings.
  */
-#if __GNUC__ >= 4 && __GNUC_MINOR__ >= 5
+#ifdef HAVE___BUILTIN_UNREACHABLE
 #define unreachable(str)    \
 do {                        \
    assert(!str);            \
    __builtin_unreachable(); \
 } while (0)
-#elif (defined(__clang__) && defined(__has_builtin))
-# if __has_builtin(__builtin_unreachable)
-#  define unreachable(str)  \
-do {                        \
-   assert(!str);            \
-   __builtin_unreachable(); \
-} while (0)
-# endif
 #endif
 
 #ifndef unreachable