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[PATCH][RFC] Enable -fstrict-overflow by default
- From: Richard Biener <rguenther at suse dot de>
- To: gcc-patches at gcc dot gnu dot org
- Date: Mon, 24 Apr 2017 13:25:07 +0200 (CEST)
- Subject: [PATCH][RFC] Enable -fstrict-overflow by default
- Authentication-results: sourceware.org; auth=none
The following makes signed overflow undefined for all (non-)optimization
levels. The intent is to remove -fno-strict-overflow signed overflow
behavior as that is not a sensible option to the user (it ends up
with the worst of both -fwrapv and -fno-wrapv). The implementation
details need to be preserved for the forseeable future to not wreck
UBSAN with either associating (-fwrapv behavior) or optimizing
(-fno-wrapv behavior).
The other choice would be to make -fwrapv the default for -O[01].
A second patch in this series would unify -f[no-]wrapv, -f[no-]trapv
and -f[no-]strict-overflow with a
-fsigned-integer-overflow={undefined,wrapping,trapping[,sanitized]}
option, making conflicts amongst the options explicit (and reduce
the number of flag_ variables). 'sanitized' would essentially map
to todays flag_strict_overflow = 0. There's another sole user
of flag_strict_overflow, POINTER_TYPE_OVERFLOW_UNDEFINED - not sure
what to do about that, apart from exposing it as different flag
alltogether.
Further patches in the series would remove -Wstrict-overflow (and
cleanup VRP for example).
Anyway, most controversical part(?) below.
Any comments on this particular patch (and the overall proposal)?
Cleaning up the options is probably a no-brainer anyways.
Thanks,
Richard.
2017-04-24 Richard Biener <rguenther@suse.de>
* common.opt (fstrict-overflow): Enable by default.
* opts.c (default_options_table): Remove OPT_fstrict_overflow entry.
Index: gcc/common.opt
===================================================================
--- gcc/common.opt (revision 247091)
+++ gcc/common.opt (working copy)
@@ -2342,7 +2342,7 @@ Common Report Var(flag_strict_aliasing)
Assume strict aliasing rules apply.
fstrict-overflow
-Common Report Var(flag_strict_overflow) Optimization
+Common Report Var(flag_strict_overflow) Init(1) Optimization
Treat signed overflow as undefined.
fsync-libcalls
Index: gcc/opts.c
===================================================================
--- gcc/opts.c (revision 247091)
+++ gcc/opts.c (working copy)
@@ -496,7 +496,6 @@ static const struct default_options defa
{ OPT_LEVELS_2_PLUS, OPT_fschedule_insns2, NULL, 1 },
#endif
{ OPT_LEVELS_2_PLUS, OPT_fstrict_aliasing, NULL, 1 },
- { OPT_LEVELS_2_PLUS, OPT_fstrict_overflow, NULL, 1 },
{ OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_freorder_blocks_algorithm_, NULL,
REORDER_BLOCKS_ALGORITHM_STC },
{ OPT_LEVELS_2_PLUS, OPT_freorder_functions, NULL, 1 },