http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57343
--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 24 May 2013, rakdver at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57343 > > --- Comment #7 from Zdenek Dvorak <rakdver at gcc dot gnu.org> --- > (In reply to Richard Biener from comment #4) > > We then fall to > > > > if (multiple_of_p (TREE_TYPE (c), c, s)) > > { > > /* If C is an exact multiple of S, then its value will be reached > > before > > the induction variable overflows (unless the loop is exited in some > > other way before). Note that the actual induction variable in the > > loop (which ranges from base to final instead of from 0 to C) may > > overflow, in which case BNDS.up will not be giving a correct upper > > bound on C; thus, BNDS_U_VALID had to be computed in advance. */ > > no_overflow = true; > > exit_must_be_taken = true; > > > > which ends up with no_overflow = true and things going downhill from here. > > This is the problem -- multiple_of_p claims that (var * 100) is a multiple of > 100, which is not the case if the multiplication overflows. I am not sure > whether this is an expected behavior of multiple_of_p, or whether this could > cause problems in its other uses. > > A conservative fix here would be to replace the multiple_of_p test here by > some > safer tests -- important special cases are: > 1) both c and s are constants and c is a multiple of s > 2) s = 1 Thanks. I'll audit other uses of multiple_of_p to see whether the current behavior is desired or a bug.
