This addresses PR30318 that is about VRP not creating anti-ranges out
of overflowing PLUS/MINUS_EXPR.  Fixing this PR can possibly make removing
undefined signed overflow assumptions from VRP less harmful.

In order to do so this patch enhances certain parts of VRP to handle
anti-ranges better and canonicalizes certain anti-ranges back to ranges.

In the quest to tackle this PR I have started to re-work int_const_binop to
get rid of the vrp_int_const_binop wrapper in VRP.  What this patch does is
expose the new proposed interface under a different name and not touch
the old one (to keep patch size down).

The new interface get's rid of the nearly unused "notrunc" argument
(and so always force_fits_type), adds a type argument and a second
output, a boolean whether the operation overflowed (regardless of
definedness or undefinedness).  This avoids creating a new node just
to set the overflow flag and also allows tracking overflow for unsigned
types just as vrp_int_const_binop tried to do.  A new force_fit_type_1
was added to allow tracking of unsigned overflow here.

We can implement both old interfaces, int_const_binop and force_fit_type
using the new helpers, but I didn't yet change those to keep the patch small.

Suggestions for a better name for int_const_binop_1 welcome ;)

Note that I will split out the fold-const.c parts into a separate patch
if the general idea is ok - I just included them with the VRP patch to
make the intended use visible.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Note this patch relies on wrapping types wrapping in two's complement
way.  I have no idea how for example Ada types with range [1, 11] is
supposed to "wrap" -- with the patch we assume that adding 5 to a
range [10,10] will result in [15, 15] as it wraps according to TYPE_PRECISION,
not TYPE_MIN/MAX_VALUE.  So this part of the VRP patch needs to
be guarded appropriately - I'm just wondering about the Ada semantics here.

Comments?

Thanks,
Richard.

2007-01-07  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/30318
        * tree.h (int_const_binop_1): Export.
        * fold-const.c (force_fit_type_1): New static function.
        (int_const_binop_1): New function.
        * tree-vrp.c (set_value_range): Canonicalize anti-ranges
        to ranges where possible.
        (extract_range_from_assert): Merge anti-ranges if possible.
        (vrp_int_const_binop): Remove.
        (extract_range_from_binary_expr): Separate MIN_EXPR and MAX_EXPR
        cases, merge PLUS_EXPR and MINUS_EXPR cases.  Handle cases
        where PLUS_EXPR and MINUS_EXPR create an anti-range.  Replace
        uses of vrp_int_const_binop by int_const_binop_1.
        (compare_range_with_value): Handle anti-range with no valid
        value.

        * gcc.dg/tree-ssa/vrp31.c: New testcase.