From 06f0850427e26cb24950de60bbe70bc192ffce6a Mon Sep 17 00:00:00 2001
From: Qi Wang <interwq@gwu.edu>
Date: Thu, 7 Mar 2019 15:58:26 -0800
Subject: [PATCH] Detect if 8-bit atomics are available.

In some rare cases (older compiler, e.g. gcc 4.2 w/ MIPS), 8-bit atomics might
be unavailable.  Detect such cases so that we can workaround.
---
 configure.ac                                  | 25 +++++++++++++++++++
 include/jemalloc/internal/atomic.h            |  7 ++++++
 .../internal/jemalloc_internal_defs.h.in      |  7 ++++++
 3 files changed, 39 insertions(+)

diff --git a/configure.ac b/configure.ac
index afaaf5de..96f76d35 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1896,6 +1896,19 @@ JE_COMPILABLE([GCC __atomic atomics], [
 ], [je_cv_gcc_atomic_atomics])
 if test "x${je_cv_gcc_atomic_atomics}" = "xyes" ; then
   AC_DEFINE([JEMALLOC_GCC_ATOMIC_ATOMICS])
+
+  dnl check for 8-bit atomic support
+  JE_COMPILABLE([GCC 8-bit __atomic atomics], [
+  ], [
+      unsigned char x = 0;
+      int val = 1;
+      int y = __atomic_fetch_add(&x, val, __ATOMIC_RELAXED);
+      int after_add = (int)x;
+      return after_add == 1;
+  ], [je_cv_gcc_u8_atomic_atomics])
+  if test "x${je_cv_gcc_u8_atomic_atomics}" = "xyes" ; then
+    AC_DEFINE([JEMALLOC_GCC_U8_ATOMIC_ATOMICS])
+  fi
 fi
 
 dnl ============================================================================
@@ -1910,6 +1923,18 @@ JE_COMPILABLE([GCC __sync atomics], [
 ], [je_cv_gcc_sync_atomics])
 if test "x${je_cv_gcc_sync_atomics}" = "xyes" ; then
   AC_DEFINE([JEMALLOC_GCC_SYNC_ATOMICS])
+
+  dnl check for 8-bit atomic support
+  JE_COMPILABLE([GCC 8-bit __sync atomics], [
+  ], [
+      unsigned char x = 0;
+      int before_add = __sync_fetch_and_add(&x, 1);
+      int after_add = (int)x;
+      return (before_add == 0) && (after_add == 1);
+  ], [je_cv_gcc_u8_sync_atomics])
+  if test "x${je_cv_gcc_u8_sync_atomics}" = "xyes" ; then
+    AC_DEFINE([JEMALLOC_GCC_U8_SYNC_ATOMICS])
+  fi
 fi
 
 dnl ============================================================================
diff --git a/include/jemalloc/internal/atomic.h b/include/jemalloc/internal/atomic.h
index bb751cfc..a76f54ce 100644
--- a/include/jemalloc/internal/atomic.h
+++ b/include/jemalloc/internal/atomic.h
@@ -3,10 +3,17 @@
 
 #define ATOMIC_INLINE JEMALLOC_ALWAYS_INLINE
 
+#define JEMALLOC_U8_ATOMICS
 #if defined(JEMALLOC_GCC_ATOMIC_ATOMICS)
 #  include "jemalloc/internal/atomic_gcc_atomic.h"
+#  if !defined(JEMALLOC_GCC_U8_ATOMIC_ATOMICS)
+#    undef JEMALLOC_U8_ATOMICS
+#  endif
 #elif defined(JEMALLOC_GCC_SYNC_ATOMICS)
 #  include "jemalloc/internal/atomic_gcc_sync.h"
+#  if !defined(JEMALLOC_GCC_U8_SYNC_ATOMICS)
+#    undef JEMALLOC_U8_ATOMICS
+#  endif
 #elif defined(_MSC_VER)
 #  include "jemalloc/internal/atomic_msvc.h"
 #elif defined(JEMALLOC_C11_ATOMICS)
diff --git a/include/jemalloc/internal/jemalloc_internal_defs.h.in b/include/jemalloc/internal/jemalloc_internal_defs.h.in
index 7914b2f6..05016b1e 100644
--- a/include/jemalloc/internal/jemalloc_internal_defs.h.in
+++ b/include/jemalloc/internal/jemalloc_internal_defs.h.in
@@ -48,9 +48,16 @@
 
 /* Defined if GCC __atomic atomics are available. */
 #undef JEMALLOC_GCC_ATOMIC_ATOMICS
+/* and the 8-bit variant support. */
+#undef JEMALLOC_GCC_U8_ATOMIC_ATOMICS
 
 /* Defined if GCC __sync atomics are available. */
 #undef JEMALLOC_GCC_SYNC_ATOMICS
+/* and the 8-bit variant support. */
+#undef JEMALLOC_GCC_U8_SYNC_ATOMICS
+
+/* Defined if 8-bit atomics are supported. */
+
 
 /*
  * Defined if __builtin_clz() and __builtin_clzl() are available.