[Bug target/12306] GOT pointer (r12) reloaded unnecessarily

[kkojima at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12306

--- Comment #4 from Kazumoto Kojima <kkojima at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #3)
> If I understand correctly, rebuilding the GOT pointer in r12 is necessary at
> function entry, since it is generally not known if r12 is a valid GOT
> pointer at function entry when mixing PIC code and non-PIC code.  Calling a
> PIC function from a non-PIC function could result in a clobbered GOT > 

Yep.  If a pic function is called from a pic function, that
save&restore can be removed.  The case like

non_pic_function:
    mov.l    r12,@-r15
    sts.l    pr,@-r15

    <use r12 as a variable x>

    <call PIC function here (r12 should not be clobbered)>

    <use r12 as a variable x>

    lds.l    @r15+,pr
    rts    
    mov.l    @r15+,r12

needs it.  If we knew that that pic function can't be called from
any non-pic functions by some additional information, we could
optimize the code with removing that save&restore r12.