| Summary: | FE_INVALID flag not set on comparison with NAN (unordered) | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Vincent Lefèvre <vincent-gcc> |
| Component: | c | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | normal | ||
| Priority: | P3 | ||
| Version: | 4.8.0 | ||
| Target Milestone: | --- | ||
| See Also: | https://gcc.gnu.org/bugzilla/show_bug.cgi?id=34678 | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2013-01-17 00:00:00 | |
| Bug Depends on: | |||
| Bug Blocks: | 16989 | ||
The comparison is dead. FENV_ACCESS is not implemented (side-effects on
FENV are not preserved). Use
if (d <= 0.0)
__asm("");
GCC uses ucomisd for the comparison, even with -fsignalling-nans.
|
GCC doesn't set the FE_INVALID flag on comparison with NAN (<=, >=, <, >), e.g. with: #include <stdio.h> #include <math.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON int main (void) { double d = NAN; int err; feclearexcept (FE_INVALID); d <= 0.0; err = ! fetestexcept(FE_INVALID); if (err) printf ("The FE_INVALID flag is not set\n"); return err; } $ gcc-snapshot --version gcc (Debian 20130113-1) 4.8.0 20130113 (experimental) [trunk revision 195136] [...] $ gcc-snapshot -std=c99 -Wall nancmp.c -o nancmp -lm nancmp.c:5:0: warning: ignoring #pragma STDC FENV_ACCESS [-Wunknown-pragmas] #pragma STDC FENV_ACCESS ON ^ nancmp.c: In function 'main': nancmp.c:13:3: warning: statement with no effect [-Wunused-value] d <= 0.0; ^ $ ./nancmp The FE_INVALID flag is not set The "statement with no effect" warning would also be incorrect once this bug is fixed.