[Bug tree-optimization/63411] [4.9/5 regression] ivopt produces wrong struct offset

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63411

amker at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |amker at gcc dot gnu.org

--- Comment #4 from amker at gcc dot gnu.org ---
(In reply to Oleg Endo from comment #3)
> (In reply to bin.cheng from comment #2)
> > >         bt/s    .L3
> > >         mov     r1,r2
> > >         add     #3,r2     <<< wrong struct offset '3'
> > But r2 is initialized with [.L14] which is _OAM3+3, so the offset actually
> > is 6 here, No?
> 
> Ouch.  Yes.  Sorry for the fuzz.
> On SH this is a performance regression (it can do only displacements that
> are scaled by the access size), but not a wrong-code regression.

We saw similar problems on arm too.  Problem is IVOPT's model doesn't know the
detail of target addressing mode.  This is should be fixed by improving
function get_address_cost, but that's just difficult to expose every target
details to middle end, especially we need to keep it simple and fast.