[Bug tree-optimization/14844] [tree-ssa] narrow types if wide result is not needed for unsigned types or when wrapping is true

[pinskia at gcc dot gnu dot org]

------- Comment #10 from pinskia at gcc dot gnu dot org  2005-11-29 01:03 -------
(In reply to comment #5)
> Once fold is able to do (int)(a+b) into (int)a + (int)b, the combine pass
> (15459) should be able to fix this.

I should note this is only valid for unsigned types and when -fwrapv is
supplied as take a being INT_MAX and b being 1 (both have the same type which
is larger than int), with (int)(a) + (int)(b)  we get an overflow which is
undefined but (int)(a+b) is defined as 0.  See PR 25125 for an example of where
this goes wrong currently from the front-end/convert.c mess.

We could define a new trees for addition where overflow is defined as wrapping.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[tree-ssa] narrow types if  |[tree-ssa] narrow types if
                   |wide result is not needed   |wide result is not needed
                   |                            |for unsigned types or when
                   |                            |wrapping is true


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844