reload question

[Ian Lance Taylor]

<tm_gccmail@kloo.net> writes:

> It will generate a lot of redundant moves to/from the accumulator because
> the accumulator is exposed much too late.
> 
> Consider the 3AC code:
> 
> add i,j,k
> add k,l,m
> 
> it will be broken down into:
> 
> mov i,a
> add j,a
> mov a,k
> mov k,a
> add l,a
> mov a,m
> 
> where the third and fourth instructions are basically redundant.

In the gcc context, the fourth instruction can be removed by the
reload CSE pass in postreload.c.  Still, obviously the generated code
is going to be bad.

I agree that gcc is not well designed to cope with an accumulator
architecture.  Reload can't cope.

Ian