------- Comment #6 from rguenth at gcc dot gnu dot org 2008-04-23 14:32 -------
-fno-tree-vrp "fixes" it, but
D.2830_35: [0, 65535]
D.2839_49: [0, 65535]
D.2840_56: [0, +INF(OVF)]
D.2829_34 = *D.2828_33;
D.2830_35 = (int) D.2829_34;
...
D.2838_48 = *D.2837_47;
D.2839_49 = (int) D.2838_48;
D.2840_56 = D.2830_35 * D.2839_49;
high_59 = D.2840_56 < 0;
looks suspiciously like a case of signed integer overflow undefinedness.
uv = x[1 + j] * x[1 + i];
high = (uv & 0x80000000) != 0;
the multiplication will be carried out in signed int because VBigDig, the
type of *x, unsigned short, promotes to int. Thus the above is equivalent to
uv = (unsigned int)((int)x[1 + j] * (int)x[1 + i]);
high = (uv & 0x80000000) != 0;
at which the compiler can conclude that the result of the multiplication
is never negative. Fix this by doing
uv = (VBigDigs)x[1 + j] * (VBigDigs)x[1 + i];
high = (uv & 0x80000000) != 0;
instead.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|WAITING |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36026
