[Bug tree-optimization/59124] [4.9/5/6 Regression] Wrong warnings "array subscript is above array bounds"

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124

--- Comment #22 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to baoshan from comment #21)
> Don't you think the range value is strange? how it is possible the range
> value is so big according the code?

j = i - 1 is actually j = i + 4294967295 because of unsigned.

Thus the problematic ranges:

   [test.c:9:13] # RANGE [4294967291, 4294967295]
   _51 = i_2 + 4294967290;

 are actually:

   [test.c:9:13] # RANGE [-5, -1]
   _51 = i_2 - 6;

but this code should have not been generated. Those ranges do seem suspicious.
Finding out how that block ends up with those ranges would be helpful. You
probably need to debug vrp or (using -fopt-info) the point where gcc gives:

test.c:7:3: note: loop turned into non-loop; it never loops.
test.c:7:3: note: loop with 5 iterations completely unrolled
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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/67553] Saturating SSE/AVX instructions do not get optimized
Date: Fri, 11 Sep 2015 17:00:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg553

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-09-11
          Component|middle-end                  |rtl-optimization
     Ever confirmed|0                           |1

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
Looks like SS_PLUS and SS_MINUS are missing in the constant folding code...