https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68499
Bug ID: 68499
Summary: Unclear STDC FP_CONTRACT behavior in non-standard
modes
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent-gcc at vinc17 dot net
Target Milestone: ---
Created attachment 36807
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36807&action=edit
example of C program based on the STDC FP_CONTRACT pragma
The following applies to:
gcc (Debian 20151030-1) 6.0.0 20151031 (experimental) [trunk revision 229615]
When I compile a C program like the attached one with
#pragma STDC FP_CONTRACT OFF
in a standard mode, the pragma is now taken into account as expected (see
PR37845 / r204460). However, in a non-standard mode such as the default gnu99
(?), it is not taken into account (a FMA is generated for an operation like
x*y+z), but one gets no warnings either. One should have one of the following
behaviors in non-standard modes:
1. The pragma is taken into account.
2. The pragma is not taken into account, but one gets a warning (making it
unknown in non-standard modes is OK).
If possible, (1) is probably the best choice, at least in gnu99 and gnu11
modes, as the user may want to disable contraction for some floating-point
algorithms while still being able to use specific GNU extensions.
