https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78386
Bill Schmidt <wschmidt at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #11 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
Looks like this is WAD. From the documentation:
-ffp-contract=style
‘-ffp-contract=off’ disables floating-point expression contraction. ‘-ffp-
contract=fast’ enables floating-point expression contraction such as forming of
fused multiply-add operations if the target has native support for them.
‘-ffp-contract=on’ enables floating-point expression contraction if allowed by
the language standard. This is currently not implemented and treated equal to
‘-ffp-contract=off’.
The default is ‘-ffp-contract=fast’.
Also, from internal commentary this default is associated with the default
standard, which is -std=gnu11. "In strict C standards comformance mode,
consider unpredictable excess precision to mean lack of IEEE 754 support. The
same applies to unpredictable contraction. For C++, and outside strict
conformance mode, do not consider these options to mean lack of IEEE 754
support." This is why using -std=c11, for example, solves the "problem."
Thus, looks like your best option is to use -ffp-contract=off to get the
desired results.
Thanks,
Bill
