Re: generic libgcc1?

[Ian Lance Taylor <ian at wasabisystems dot com>]

Maksim <maksim@mioffe.com> writes:

> Is it the case that all of libgcc1 _has_ to be implemented by the
> target-specific part of the backend?  Isn't it possible to implement a lot
> of it in C, just as it's done with libgcc2?  (i.e., implement mulsi3 in terms
> of addsi3 and so on)  I feel like I'm missing something.

You can implement mulsi3 in terms of addsi3, but you do have to do it
either in the RTL or in libgcc1.  gcc won't do it for you.  You must
either have a mulsi3 pattern or you must have a __mulsi3 function.

Well, that isn't 100% true, since I think gcc will implement mulsi3 in
terms of muldi3 if the latter is available.  But gcc won't implement
mulsi3 in terms of addsi3.

This is probably because a __mulsi3 written in hand-coded assembler
will normally be better than whatever gcc comes up with.  But if you
really think it would be useful to implement mulsi3 in terms of
addsi3, then the place to add the code would be expand_binop() in
optabs.c.

Ian