> I noticed that several testcases in the GMP-4.3.2 test suite are failing now > which did not happen with GCC 4.9.0. I debugged the first one, > mpz/convert, and found the file mpn/generic/get_str.c was miscompiled. > > mpn/get_str.c.132t.dse2: > pretmp_183 = (sizetype) chars_per_limb_80; > pretmp_184 = -pretmp_183; > _23 = chars_per_limb_80 + 4294967295; > _68 = (sizetype) _23; > _28 = _68 + pretmp_184; > > mpn/get_str.c.133t.forwprop4: > _28 = 4294967295; > > > That is wrong, because chars_per_limb is unsigned, and it is not zero. > So the right result should be -1. This makes the loop termination in that > function fail.
Can't we compute the right result in this case? 4294967295 is almost -1. > The attached patch fixes these regressions, and because the reasoning > depends on the TYPE_OVERFLOW_UNDEFINED attribute, a strict overflow warning > has to be emitted here, at least for widening conversions. Saturating, floating-point and fixed-point types are already excluded here, see the beginning of the function. -- Eric Botcazou
