Merge pull request #170 from microsoft/gcc-warning

Addressing #168

CMakeLists.txt

@@ -33,6 +33,14 @@ macro(warnings_high)
       add_compile_options(-Wsign-conversion)
     endif ()
     add_compile_options(-Wall -Wextra -Werror -Wundef)
+    # There are a few places with subtle reasons for array access being correct
+    # GCC's warnings are too aggressive and incorrectly assume the code is wrong.
+    # Disabling only in Release is so the ASSUME can be mapped to assert and check
+    # at runtime in debug.  This ensures we are covering the cases of concern with 
+    # debug checks, but not incurring runtime penalties in release.
+    if ((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") AND (CMAKE_BUILD_TYPE STREQUAL "Release"))
+      add_compile_options(-Wno-array-bounds)
+    endif ()
   endif()
 endmacro()
 

src/ds/defines.h

@@ -62,6 +62,12 @@ namespace snmalloc
 #else
 #  if __has_builtin(__builtin_assume)
 #    define SNMALLOC_ASSUME(x) __builtin_assume((x))
+#  elif defined(_MSC_VER)
+#    define SNMALLOC_ASSUME(x) __assume((x));
+#  elif defined(__GNUC__)
+#    define SNMALLOC_ASSUME(x) \
+      if (!(x)) \
+        __builtin_unreachable();
 #  else
 #    define SNMALLOC_ASSUME(x) \
       do \