Check for __builtin_unreachable at configure time
Add a configure check for __builtin_unreachable instead of basing its
availability on the __GNUC__ version. On OS X using gcc (a real gcc, not the
bundled version that's just a gcc front-end) leads to a linker assertion:
https://github.com/jemalloc/jemalloc/issues/266
It turns out that this is caused by a gcc bug resulting from the use of
__builtin_unreachable():
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57438
To work around this bug, check that __builtin_unreachable() actually works at
configure time, and if it doesn't use abort() instead. The check is based on
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57438#c21.
With this `make check` passes with a homebrew installed gcc-5 and gcc-6.
diff --git a/configure.ac b/configure.ac
index 7f19715..6fe366c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1050,6 +1050,23 @@
fi
AC_SUBST([enable_cache_oblivious])
+
+
+JE_COMPILABLE([a program using __builtin_unreachable], [
+void foo (void) {
+ __builtin_unreachable();
+}
+], [
+ {
+ foo();
+ }
+], [je_cv_gcc_builtin_unreachable])
+if test "x${je_cv_gcc_builtin_ffsl}" = "xyes" ; then
+ AC_DEFINE([JEMALLOC_INTERNAL_UNREACHABLE], [__builtin_unreachable])
+else
+ AC_DEFINE([JEMALLOC_INTERNAL_UNREACHABLE], [abort])
+fi
+
dnl ============================================================================
dnl Check for __builtin_ffsl(), then ffsl(3), and fail if neither are found.
dnl One of those two functions should (theoretically) exist on all platforms
diff --git a/include/jemalloc/internal/jemalloc_internal_defs.h.in b/include/jemalloc/internal/jemalloc_internal_defs.h.in
index 7de0cf7..22396b7 100644
--- a/include/jemalloc/internal/jemalloc_internal_defs.h.in
+++ b/include/jemalloc/internal/jemalloc_internal_defs.h.in
@@ -189,6 +189,12 @@
#undef JEMALLOC_TLS
/*
+ * Used to mark unreachable code to quiet "end of non-void" compiler warnings.
+ * Don't use this directly; instead use unreachable() from util.h
+ */
+#undef JEMALLOC_INTERNAL_UNREACHABLE
+
+/*
* ffs*() functions to use for bitmapping. Don't use these directly; instead,
* use ffs_*() from util.h.
*/
diff --git a/include/jemalloc/internal/util.h b/include/jemalloc/internal/util.h
index a0c2203..aee00d6 100644
--- a/include/jemalloc/internal/util.h
+++ b/include/jemalloc/internal/util.h
@@ -61,30 +61,20 @@
# define JEMALLOC_CC_SILENCE_INIT(v)
#endif
-#define JEMALLOC_GNUC_PREREQ(major, minor) \
- (!defined(__clang__) && \
- (__GNUC__ > (major) || (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor))))
-#ifndef __has_builtin
-# define __has_builtin(builtin) (0)
-#endif
-#define JEMALLOC_CLANG_HAS_BUILTIN(builtin) \
- (defined(__clang__) && __has_builtin(builtin))
-
#ifdef __GNUC__
# define likely(x) __builtin_expect(!!(x), 1)
# define unlikely(x) __builtin_expect(!!(x), 0)
-# if JEMALLOC_GNUC_PREREQ(4, 6) || \
- JEMALLOC_CLANG_HAS_BUILTIN(__builtin_unreachable)
-# define unreachable() __builtin_unreachable()
-# else
-# define unreachable() abort()
-# endif
#else
# define likely(x) !!(x)
# define unlikely(x) !!(x)
-# define unreachable() abort()
#endif
+#if !defined(JEMALLOC_INTERNAL_UNREACHABLE)
+# error JEMALLOC_INTERNAL_UNREACHABLE should have been defined by configure
+#endif
+
+#define unreachable() JEMALLOC_INTERNAL_UNREACHABLE()
+
#include "jemalloc/internal/assert.h"
/* Use to assert a particular configuration, e.g., cassert(config_debug). */