Consider the following piece of code, derived from the secnds-1.f test case (with some changes I'd added to avoid the 20ms arbitrary tolerance):
C {dg-do run} character*20 dum1, dum2, dum3 real t1, t1a, t2, t2a real dat1, dat2 integer i, j, values(8) t1 = secnds (0.0) call date_and_time (dum1, dum2, dum3, values) t1a = secnds (0.0) dat1 = 0.001*real (values(8)) + real (values(7)) + & 60.0*real (values(6)) + 3600.0* real (values(5)) C The following line is critical here. C write (*,*) (((dat1 - t1) < 0.) .or. ((dat1 - t1) > (t1a - t1))) if (((dat1 - t1) < 0.) .or. ((dat1 - t1) > (t1a - t1))) then write (*,*) (((dat1 - t1) < 0.) .or. ((dat1 - t1) > (t1a - t1))) write (*,*) dat1, t1, t1a, dat1-t1, t1a-t1 call abort () end if end If I run this through the usual testsuite apparatus, it will fail on about 30% (on average) of the optimized runs, but never (so far as I've seen) with -O0. The output, though, usually looks like this: F 16806.37 16806.37 16806.37 0.000000 0.000000 Note the "F", for the exact check that just evaluated as true in the IF statement. If I uncomment the WRITE statement prior to the IF, the failures go away. -- Summary: SECNDS() or DATE_AND_TIME() intrinsic optimized incorrectly. Product: gcc Version: 4.3.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: fortran AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: brooks at gcc dot gnu dot org GCC build triplet: i686-pc-linux-gnu GCC host triplet: i686-pc-linux-gnu GCC target triplet: i686-pc-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30752