[Bug tree-optimization/54471] [4.8 Regression] FAIL: gcc.dg/sms-8.c execution test

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54471

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-11-21 14:42:13 UTC ---
Created attachment 28755
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28755
gcc48-pr54471.patch

Untested fix.  I believe the bug is in invalid canonicalization.  When
sizem1 is { -1, -1 } double_int, sizem1 + double_int_one is { 0, 0 }, as it
wrapped, instead of { 0, 0, 1, 0 } quad_int.  And if min0 or min1 is zero, then
size - min{0,1} is also zero, and so is very likely smaller than max{0,1}
(unless min{0,1} == max{0,1}), but we still don't want to "canonicalize" that
to signed.  IMHO testing min2.is_zero () is sufficient, as min0 or min1 should
be a valid double_int in the range 0 to { -1, -1 }, which is always smaller
than the maximum unsigned integer + 1 in infinite precision and thus min2
should never be zero, unless size overflowed to 0 and min{0,1} is zero.