Re: [PATCH] Add XINSN macro and use it within NEXT_INSN/PREV_INSN (was Re: [PATCH] Force rtl templates to be inlined)

[Jeff Law <law at redhat dot com>]

On 09/04/14 14:04, David Malcolm wrote:
> On Tue, 2014-09-02 at 19:50 +0200, Andi Kleen wrote:
> > > I suspect the bulk of them currently are coming from the safe_as_a
> > > <rtx_insn *> calls within NEXT_INSN and PREV_INSN; do you happen to have
> > > information handy on that?
> >
> > Yes that's right:
> >
> > -   1.03%  lto1                    [.] bool is_a_helper<rtx_insn*>::test<rtx_def>(rtx_def*)                                                     â
> >     - bool is_a_helper<rtx_insn*>::test<rtx_def>(rtx_def*)                                                                                       â
> >        - 92.20% bool is_a<rtx_insn*, rtx_def>(rtx_def*)                                                                                          â
> >           - 98.53% rtx_insn* safe_as_a<rtx_insn*, rtx_def>(rtx_def*)                                                                             â
> >              - 73.28% NEXT_INSN(rtx_insn const*)                                                                                                 â
>
> The is_a_helper for rtx_insn * is non-trivial, so it may be worth
> avoiding it, even when inlined.
>
> The attached patch rewrites the inline NEXT_INSN/PREV_INSN to avoid
> doing the safe_as_a, instead tightening up the interface so that one can
> only set them to an insn, and introducing a new XINSN access macro and
> corresponding rt_insn member of the union.
>
> Bootstrapped on x86_64-unknown-linux-gnu (Fedora 20), and has been
> rebuilt as part of a config-list.mk build for all working configurations
> (albeit with other patches for the latter case).
>
> OK for trunk?
So is this just to deal with the overhead in the safe_as_a helper until 
we can strengthen more code?  And is that overhead significant in an 
optimized build?

Would an alternate approach be to make the checking in safe_as_a 
conditionalized on ENABLE_CHECKING?

jeff