[Bug tree-optimization/55022] [4.8/4.9 Regression] air.f90 is miscompliled with -m64 -O2 -fgraphite-identity after revision 190619

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55022

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #18 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Mircea Namolaru from comment #17)
> Vladimir Kargov, Tobias Grosser and me found that the problem is caused by
> incorrect folding of the floord operator. As a result Cloog translates the
> expression
> -4294967296*floord(_19-i_17,4294967296)
> to the tree-SSA expression
> 4294967296*floord(_19-i_17,-4294967296)
> 
> This is wrong, in the first case floord is 0 and in the second is -1.

Not sure where that "folding" happens or what "floord" is, but if you
are refering to negate_expr () negating a /[fl] CST as a /[fl] -CST
then yes, that looks suspicious.  OTOH the division variant tree codes
don't appear in the IL very often so it's hard to notice these mistakes.
Testing

Index: gcc/fold-const.c
===================================================================
*** gcc/fold-const.c    (revision 209292)
--- gcc/fold-const.c    (working copy)
*************** negate_expr_p (tree t)
*** 484,491 ****

      case TRUNC_DIV_EXPR:
      case ROUND_DIV_EXPR:
-     case FLOOR_DIV_EXPR:
-     case CEIL_DIV_EXPR:
      case EXACT_DIV_EXPR:
        /* In general we can't negate A / B, because if A is INT_MIN and
         B is 1, we may turn this into INT_MIN / -1 which is undefined
--- 484,489 ----
*************** fold_negate_expr (location_t loc, tree t
*** 682,689 ****

      case TRUNC_DIV_EXPR:
      case ROUND_DIV_EXPR:
-     case FLOOR_DIV_EXPR:
-     case CEIL_DIV_EXPR:
      case EXACT_DIV_EXPR:
        /* In general we can't negate A / B, because if A is INT_MIN and
         B is 1, we may turn this into INT_MIN / -1 which is undefined
--- 680,685 ----