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Re: Compact regsiter allocation
> From: Ian Lance Taylor <email@example.com>
> To: Jamie Prescott <firstname.lastname@example.org>
> Cc: email@example.com
> 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
> > with ad-hoc register naming, it starts generating holes.
> > The extra renaming pass, is it something available today?
> > 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.