http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092
--- Comment #14 from rguenther at suse dot de <rguenther at suse dot de> --- On Thu, 6 Feb 2014, jakub at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 > > --- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > (In reply to Richard Biener from comment #12) > > (In reply to Andreas Schwab from comment #11) > > > If a function is not allowed to change errno this must be explicitly > > > documented. > > > > That means > > > > Index: gcc/tree-ssa-alias.c > > =================================================================== > > --- gcc/tree-ssa-alias.c.orig 2014-02-06 15:43:42.138266256 +0100 > > +++ gcc/tree-ssa-alias.c 2014-02-06 15:43:33.046266882 +0100 > > @@ -1847,7 +1847,9 @@ call_may_clobber_ref_p_1 (gimple call, a > > ao_ref dref; > > ao_ref_init_from_ptr_and_size (&dref, ptrptr, > > TYPE_SIZE_UNIT (ptr_type_node)); > > - return refs_may_alias_p_1 (&dref, ref, false); > > + return (refs_may_alias_p_1 (&dref, ref, false) > > + || (flag_errno_math > > + && targetm.ref_may_alias_errno (ref))); > > } > > /* Freeing memory kills the pointed-to memory. More importantly > > the call has to serve as a barrier for moving loads and stores > > > > is necessary. > > For posix_memalign? I think errno can contain any value, except that library > is not allowed to clear errno. > So, IMHO *p = 1; posix_memalign (...); return *p; can be still optimized into > return 1;, because if p = &errno; then *p after the call has undefined value > (just known not to be zero). But on allocation failure posix_memalign may set it to 2, no? So for errno = 0; posix_memalign () errno = 0; ptr = malloc (); if (!ptr) perror (); we may not DSE the 2nd errno = 0 store. Richard.
