Hi,
In common.opt, -ffp-contract=fast is set as the default for GCC. But
then it gets disabled in c-family/c-opts.c if you are using ISO C
(e.g. with -std=c99).
The reason for this patch is that if you have also specified
-funsafe-math-optimizations (or -Ofast or -ffast-math) then it is
likely your preference to have -ffp-contract=fast on, so you can
generate fused multiply adds (fma standard pattern).
This patch works by blocking the override if you have
-funsafe-math-optimizations (directly or indirectly), causing fused
multiply add to be used in the places where we might hope to see it.
(I had considered forcing -ffp-contract=fast on in opts.c if you have
-funsafe-math-optimizations, but it is already on by default ... and
it didn't work either! The problem is that it is forced off unless
you have explicitly asked for -ffp-contract=fast at the command-line.)
Standard regressions passed.
OK for trunk or stage 1?
Cheers,
Ian
10-03-2014 Ian Bolton <ian.bol...@arm.com>
* gcc/c-family/c-opts.c (c_common_post_options): Don't override
-ffp-contract=fast if unsafe-math-optimizations is on.diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index b7478f3..92ba481 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -834,7 +834,8 @@ c_common_post_options (const char **pfilename)
if (flag_iso
&& !c_dialect_cxx ()
&& (global_options_set.x_flag_fp_contract_mode
- == (enum fp_contract_mode) 0))
+ == (enum fp_contract_mode) 0)
+ && flag_unsafe_math_optimizations == 0)
flag_fp_contract_mode = FP_CONTRACT_OFF;
/* By default we use C99 inline semantics in GNU99 or C99 mode. C99
