Overwhelmed by GCC frustration

[Oleg Endo]

On Wed, 2017-08-16 at 15:53 +0200, Georg-Johann Lay wrote:
>Â 
> This means it's actually waste of time to work on these
> backends.  The code will finally end up in the dustbin as cc0
> backends are considered undesired ballast that has to be
> "jettisoned".
> 
> "Deprecate all cc0" is just a nice formulation of "deprecate
> most of the cc0 backends".
> 
> Just the fact that the backends that get most attention and attract
> most developers don't use cc0 doesn't mean cc0 is a useless device.

The desire to get rid of old, crusty and unmaintained stuff is somehow
understandable...


> First of all, LRA cannot cope with cc0 (Yes, I know deprecating
> cc0 is just to deprecate all non-LRA BEs).  LRA asserts that
> accessing the frame doesn't change condition code. LRA doesn't
> provide replacement for LEGITIMITE_RELOAD_ADDRESS.  Hence LRA
> focusses just comfortable, orthogonal targets.

It seems LRA is being praised so much, but all those niche BEs and
corner cases get zero support. Â There are several known instances of SH
code regressions with LRA, and that's why I haven't switched it to
LRA. 

I think the problem is that it's very difficult to make a register
allocator that works well for everything. Â The last attempt ended in
reload. Â And eventually LRA will go down the same route. Â So instead of
trying to fit a round peg in a square hole, maybe we should just have
the options for round and square pegs and holes.


Cheers,
Oleg