[Patch] PR68137, drop constant overflow flag in adjust_range_with_scev when possible

[Jiong Wang]

As reported by pr68137 and pr68326, r230150 caused new issues.

Those ICEs are caused by adjust_range_with_scev getting range with
overflowed constants min or max. So given there are too many places to
generate OVF, we do a check in adjust_range_with_scev, to drop OVF flag
when it's uncessary. This should fix the OVF side-effect caused by
r230150.

A simple regression testcase is included in this patch.

bootstrap OK on x86-64 and aarch64, regression ok on both.

For more background, please see discussion at

   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68317

OK for trunk?

2015-11-23  Richard Biener  <rguenth@gcc.gnu.com>
             Jiong Wang  <jiong.wang@arm.com>

gcc/
   PR tree-optimization/68137
   PR tree-optimization/68326
   * tree-vrp.c (adjust_range_with_scev): Call drop_tree_overflow if the
   final min and max are not infinity.

gcc/testsuite/
   * gcc.dg/pr68139.c: New testcase.

--
Regards,
Jiong

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