Re: new register allocator and HARD_REGNO_CALL_PART_CLOBBERED

[Daniel Berlin <dberlin at dberlin dot org>]

On Thursday, May 1, 2003, at 03:21  PM, Herman ten Brugge wrote:

> Dale Johannesen wrote :
> > On Wednesday, April 30, 2003, at 12:31  PM, Herman ten Brugge wrote:
> >
> > > Hello,
> > >
> > > I found a problem with the -fnew-ra option of the compiler. I 
> > > analysed
> > > the problem and found that the macro HARD_REGNO_CALL_PART_CLOBBERED
> > > is not used by the new register allocator.
> > > I think this is also a bit difficult to implement because we now
> > > have to check the mode for every register that is used during a
> > > CALL_INSN.
> >
> > You can try the following (mail may have screwed up spacing).  It may
> > result in even worse code than your patch, but maybe it's better than
> > trying to work around this new-ra problem in individual targets.
> > (Untested, I do not have a c4x.)
>
> I do not think the problem is in df.c.
It is.

> The code in df.c walks through the
> rtl and sets clobbered/used register info.
Right, and HARD_REGNO_CALL_PART_CLOBBERED says that hard regs are 
clobbered.
Notice that the portion of the code modified in df.c is dealing with 
hard registers that are killed by calls.

>  We do not yet know what mode
> the hard registers will get (reg_raw_mode can not be used here). The 
> mode
> is assigned in the new-ra pass.
This has nothnig to do with anything.

> We run df.c when no hard registers are set yet, only pseudo registers
> are set.
This is wrong.
The code in question in df.c is determining what regs are killed by 
calls.
This is *exactly* the right place to do it.

> HARD_REGNO_CALL_PART_CLOBBERED works only on hard registers,
> so how should this work? See how HARD_REGNO_CALL_PART_CLOBBERED is
> used in local_alloc.c and global.c.
Because they don't use df.c for register info, like new-ra does.