Re: fuse-caller-save - hook format

[Tom de Vries <Tom_deVries at mentor dot com>]

On 22-04-14 18:18, Richard Sandiford wrote:
> Tom de Vries <Tom_deVries@mentor.com> writes:
>
> > On 22-04-14 17:27, Richard Sandiford wrote:
> > > Tom de Vries <Tom_deVries@mentor.com> writes:
> > > > 2. post_expand_call_insn.
> > > > A utility hook to facilitate adding the clobbers to CALL_INSN_FUNCTION_USAGE.
> > >
> > > Why is this needed though?  Like I say, I think targets should update
> > > CALL_INSN_FUNCTION_USAGE when emitting calls as part of the call expander.
> > > Splitting the functionality of the call expanders across the define_expand
> > > and a new hook just makes things unnecessarily complicated IMO.
> >
> > Richard,
> >
> > It is not needed, but it is convenient.
> >
> > There are targets where the define_expands for calls use the rtl template.
> > Having to add clobbers to the CALL_INSN_FUNCTION_USAGE for such a target means
> > you cannot use the rtl template any more and instead need to generate
> > all needed
> > RTL insns in C code.
> >
> > This hook means that you can keep using the rtl template, which is less
> > intrusive for those targets.

[ switching order of questions ]
> Which target do you have in mind?

Aarch64.

> But if the target is simple enough to use a single call pattern for call
> cases, wouldn't it be possible to add the clobber directly to the call
> pattern?

I think that can be done, but that feels intrusive as well. I thought the reason 
that we added these clobbers to CALL_INSN_FUNCTION_USAGE was exactly because we 
did not want to add them to the rtl patterns?

But, if the maintainer is fine with that, so am I.

Richard Earnshaw,

are you ok with adding the IP0_REGNUM/IP1_REGNUM clobbers to all the call 
patterns in the Aarch64 target?

The alternatives are:
- rewrite the call expansions not to use the rtl templates, and add the clobbers
  there to CALL_INSN_FUNCTION_USAGE
- get the post_expand_call_insn hook approved and use that to add the clobbers
  to CALL_INSN_FUNCTION_USAGE.

what is your preference?

Thanks,
- Tom