> From: Ian Lance Taylor <i...@google.com>
> To: Jamie Prescott <jpre...@yahoo.com>
> Cc: gcc@gcc.gnu.org
> Sent: Thursday, May 14, 2009 10:09:40 PM
> Subject: Re: Compact regsiter allocation
>
> Jamie Prescott writes:
>
> >> Normally gcc will allocate registers in the order they are listed in
> >> REG_ALLOC_ORDER, which defaults to increasing numeric order. gcc won't
> >> normally allocate register sparsely. That said, it is quite possible
> >> for gcc to allocate a register and then discover that it need not be
> >> allocated. There isn't currently any way to request that gcc tighten up
> >> the register allocation. That would probably require another
> >> optimization pass to consistently rename registers when there is a hole
> >> in the allocation order.
> >
> > Yep, usually it allocates compact, but I noticed that when there's some
> > inline
> assembly
> > with ad-hoc register naming, it starts generating holes.
> > The extra renaming pass, is it something available today?
>
> No.
>
> > If not, what is the best spot (in the normal GCC target hooks) to trigger
> > it?
> Where the
> > full insn tree is passed in such hook (if it's not a global)?
>
> TARGET_MACHINE_DEPENDENT_REORG. It will be invoked once for each
> function, and can access and modify the complete RTL insn tree.
Perfect, thanks!
- Jamie
