On Thu, 9 Jun 2022, Jason Merrill wrote:
> On 6/9/22 09:00, Patrick Palka wrote:
> > This performs one of the optimizations added by the previous
> > patch to lookup_template_class, to instantiate_template as well.
> > (For the libstdc++ ranges tests this optimization appears to be
> > effective around 30% of the time, i.e. 30% of the time context of 'tmpl'
> > is non-dependent while the context of 'gen_tmpl' is dependent.)
>
> If this is a significant optimization, how about doing it in tsubst_aggr_type
> rather than its callers?
I'm not sure how we'd do this optimization in tsubst_aggr_type?
I haven't observed any significant time/memory improvements based on my
limited benchmarking, but I can imagine for deeply nested templates it
could be significant. And avoiding redundant work should hopefully help
streamline debugging I suppose.
>
> > gcc/cp/ChangeLog:
> >
> > * pt.cc (instantiate_template): Don't substitute the context
> > of the most general template if that of the partially
> > instantiated template is non-dependent.
> > ---
> > gcc/cp/pt.cc | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index e021c254872..208daad298a 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -21661,8 +21661,14 @@ instantiate_template (tree tmpl, tree orig_args,
> > tsubst_flags_t complain)
> > ++processing_template_decl;
> > if (DECL_CLASS_SCOPE_P (gen_tmpl))
> > {
> > - tree ctx = tsubst_aggr_type (DECL_CONTEXT (gen_tmpl), targ_ptr,
> > - complain, gen_tmpl, true);
> > + tree ctx;
> > + if (!uses_template_parms (DECL_CONTEXT (tmpl)))
> > + /* If the context of the partially instantiated template is already
> > + non-dependent, then we might as well use it. */
> > + ctx = DECL_CONTEXT (tmpl);
> > + else
> > + ctx = tsubst_aggr_type (DECL_CONTEXT (gen_tmpl), targ_ptr,
> > + complain, gen_tmpl, true);
> > push_nested_class (ctx);
> > }
> >
>
>
