http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50865
--- Comment #8 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-10-25 16:18:12 UTC --- On Tue, 25 Oct 2011, jaak at ristioja dot ee wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50865 > > --- Comment #7 from Jaak Ristioja <jaak at ristioja dot ee> 2011-10-25 > 16:08:19 UTC --- > (In reply to comment #6) > > /* X % -Y is the same as X % Y. */ > > (fold-const.c:fold_binary_loc) would probably be what's wrong here. > > On the other hand > https://www.securecoding.cert.org/confluence/display/seccode/INT32-C.+Ensure+that+operations+on+signed+integers+do+not+result+in+overflow#INT32-C.Ensurethatoperationsonsignedintegersdonotresultinoverflow-Modulo > also refers to C99, saying that X % Y and X % -Y are equivalent. Well, they are equivalent where they are both defined, or if you apply C99 rules to infinite-precision integers. The problem here is that INT_MIN % -1 is undefined (explicitly in C1X) and so a transformation of INT_MIN % 1 into INT_MIN % -1 is unsafe (the other way round, transforming undefined behavior to defined, is fine at least in the absence of -ftrapv).
