On Sun, Jun 22, 2014 at 9:14 AM, Bernd Edlinger <bernd.edlin...@hotmail.de> wrote: > Hi, > > 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. > > The reason for this is in this check-in: > > r210807 | ebotcazou | 2014-05-22 16:32:56 +0200 (Thu, 22 May 2014) | 3 lines > > * tree-ssa-forwprop.c (associate_plusminus): Extend (T)(P + A) - (T)P > -> (T)A transformation to integer types. > > > Because it implicitly assumes that integer overflow is not allowed with all > types, > including unsigned int.
Hmm? But the transform is correct if overflow wraps. And it's correct if overflow is undefined as well, as (T)A is always well-defined (implementation defined) if it is a truncation. So we match the above an try to transform it to (T)P + (T)A - (T)P. That's wrong if the conversion is extending I think. Richard. > > 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. > > > Boot-strapped and regression-tested on x86_64-linux-gnu with all languages, > including Ada. > OK for trunk? + if (!TYPE_SATURATING (TREE_TYPE (a)) this is already tested at the very beginning of the function. + && !FLOAT_TYPE_P (TREE_TYPE (a)) + && !FIXED_POINT_TYPE_P (TREE_TYPE (a)) likewise. + || (!POINTER_TYPE_P (TREE_TYPE (p)) + && INTEGRAL_TYPE_P (TREE_TYPE (a)) + && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (a))) INTEGRAL_TYPE_P are always !POINTER_TYPE_P. > > Thanks > Bernd. >
