PR37363: PR36090 and PR36182 all over again

[Paolo Bonzini]

>> 3) adding a check that the MINUS is a legitimate address, and only wrap
>> it in CONST if it is.
> 
> s/address/constant/; it's not clear that it's used as an address
> at that point; it's just two expressions that gcc tries to
> reduce.

Right.

> But I get the point; I'm leaning towards something like
> strengthening that it's a legitimate constant.  See
> <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36182#c12> and
> other comments in that PR.  But... should we really redefine
> LEGITIMATE_CONSTANT_P and its documentation at this stage?

We can do it incrementally.  For now, only redefine
LEGITIMATE_CONSTANT_P on CRIS and in the documentation, and use it in
simplify_plus_minus.  For 4.5, we can look at other places using
gen_rtx_CONST and strengthen them too.

Paolo