http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48580
--- Comment #20 from Marc Glisse <glisse at gcc dot gnu.org> --- (In reply to Zack Weinberg from comment #5) > Addendum: what would *you* describe as the correct C idiom for > ensuring that the product of two signed integers was positive and did > not overflow the range of a same-sized signed integer, assuming > nothing about either multiplicand? The most natural way to do it depends on whether you have access to a wider type (and may rely on modular casts to signed integer types as guaranteed by gcc). For instance if you want a non-negative result that fits an int: return x * (unsigned long long)(y) <= __INT_MAX__; or if you only care about signed overflow and not the sign of the result: long long l = x * (long long)(y); return l == (int) l; The value of the overflow flags after a multiplication doesn't seem modeled in i386.md currently (apart from "clobbered"), so it won't be used, but the code generated is not too horrible.
