[Bug rtl-optimization/54524] [4.6/4.7/4.8 Regression] Spurious add on sum of bitshifts (forward-propagate issue)

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54524

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-09-19
     Ever Confirmed|0                           |1
           Severity|major                       |normal

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-09-19 01:39:38 UTC ---
As far as I can tell, Richard's patch just exposed a latent bug as I was
looking into the dumps.



In insn 28, replacing
 (ltu:SI (reg:SI 231 [+4 ])
        (reg:SI 229 [+4 ]))
 with (const_int 1 [0x1])
Changed insn 28
deferring rescan insn with uid = 28.

after cse:
(insn 27 43 28 2 (set (reg:SI 231 [+4 ])
        (plus:SI (reg:SI 229 [+4 ])
            (const_int 0 [0]))) t.c:24 10 {*addsi3}
     (nil))

(insn 28 27 29 2 (set (reg:SI 212)
        (ltu:SI (reg:SI 231 [+4 ])
            (reg:SI 229 [+4 ]))) t.c:24 521 {*sltu_sisi}
     (nil))

So this is a bug in CSE which is not simplifying that addsi3 into just a move
for some reason.