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From: "rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94899] Failure to optimize out add before
 compare with INT_MIN
Date: Fri, 01 May 2020 08:47:46 +0000
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X-Bugzilla-Component: tree-optimization
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X-Bugzilla-Keywords: easyhack, missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94899

rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |easyhack
             Status|RESOLVED                    |NEW
   Last reconfirmed|                            |2020-05-01
                 CC|                            |rsandifo at gcc dot gnu.org
         Resolution|INVALID                     |---
     Ever confirmed|0                           |1

--- Comment #4 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.or=
g> ---
Reopening because...

(In reply to Andrew Pinski from comment #2)
> This is invalid as 0x80000000 is unsigned (C90/C++03) or long (C99/C++11)=
 in
> type.
> Which means then overflow is not undefined but rather wrapping.

It's unsigned int for C99/C++11 too (see the different handling of
decimal-literals and other integer-literals in [lex.icon.type]).

This means that the result of the addition is also unsigned,
For the specific value of 0x80000000, the transformation is monotonic,
so the optimisation is valid and well-defined.=