On 06/17/2013 06:02 PM, Sandra Loosemore wrote:
I had another thought: perhaps -fstrict-volatile-bitfields could remain
the default on targets where it currently is, but it can be overridden
by an appropriate -std= option. Perhaps also GCC could give an error if
-fstrict-volatile-bitfields is given explicitly with an incompatible
-std= option.
Like this. This patch is intended to be applied on top of the other 5
pieces in this series, although in theory it's independent of them. OK
to commit, and does this resolve the objection to part 3?
-Sandra
2013-06-19 Sandra Loosemore <san...@codesourcery.com>
gcc/c-family/
* c-opts.c (c_common_post_options): Check for conflict between
-std= and -fstrict-volatile-bitfields.
gcc/
* doc/invoke.texi (Code Gen Options): Document what happens when
-fstrict-volatile-bitfields conflicts with -std=.
Index: gcc/c-family/c-opts.c
===================================================================
--- gcc/c-family/c-opts.c (revision 199963)
+++ gcc/c-family/c-opts.c (working copy)
@@ -813,6 +813,18 @@ c_common_post_options (const char **pfil
C_COMMON_OVERRIDE_OPTIONS;
#endif
+ /* C11 and C++11 specify a memory model that is incompatible with
+ -fstrict-volatile-bitfields. Warn if that option is given explicitly
+ and prevent backends from defaulting to turning it on. */
+ if (flag_isoc11 || cxx_dialect >= cxx11)
+ {
+ if (flag_strict_volatile_bitfields > 0)
+ warning (0, "-fstrict-volatile-bitfields conflicts with the "
+ "C11 and C++11 memory model");
+ else
+ flag_strict_volatile_bitfields = 0;
+ }
+
/* Excess precision other than "fast" requires front-end
support. */
if (c_dialect_cxx ())
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi (revision 199963)
+++ gcc/doc/invoke.texi (working copy)
@@ -20899,4 +20899,12 @@
AAPCS, @option{-fstrict-volatile-bitfields} is the default.
+Note that @option{-fstrict-volatile-bitfields} is incompatible with
+the bit-field access behavior required by the ISO C11 and C++11
+standards. GCC warns if @option{-fstrict-volatile-bitfields} is given
+explicitly with an incompatible @option{-std=} option. On targets
+that otherwise default to @option{-fstrict-volatile-bitfields},
+providing an incompatible @option{-std=} option implicitly disables
+@option{-fstrict-volatile-bitfields}.
+
@item -fsync-libcalls
@opindex fsync-libcalls
