[Bug tree-optimization/30911] VRP fails to eliminate range checks in Ada code

["baldrick at free dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #42 from baldrick at free dot fr  2007-03-02 09:16 -------
Subject: Re:  VRP fails to eliminate range checks in Ada code

> Thaks for the detective work!  I sort of expected the fold patch to be weird or
> have no effect - but it was needed only (for the testcase) to get rid of the
> target_first == 128 comparison, as that is confusing VRP.  Basically after this
> comparison we conclude target_first != 128 and drop the earlier target_first !=
> 10
> assertion which is the one we can use to optimize the later comparisons.
> 
> So the other solution is to simply not record out-of-bounds assertions.

I think fold needs to be fixed, whether or not your fold patch goes in.
After all, fold is clearly willing to do create objects like X^Y which
take values outside of the range of the type.  Once such objects are
floating around, any serious use of TYPE_MAX_VALUE or TYPE_MIN_VALUE
(when they are non-trivial) will almost certainly give wrong results,
as shown by your fold patch.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30911