On Thu, 9 Jun 2022, Patrick Palka wrote:
> On Thu, 9 Jun 2022, Jason Merrill wrote:
>
> > On 6/8/22 14:21, Patrick Palka wrote:
> > > When substituting a class template specialization, tsubst_aggr_type
> > > substitutes the TYPE_CONTEXT before passing it to lookup_template_class.
> > > This appears to be unnecessary, however, because the the initial value
> > > of lookup_template_class's context parameter is unused outside of the
> > > IDENTIFIER_NODE case, and l_t_c performs its own substitution of the
> > > context, anyway. So this patch removes the redundant substitution in
> > > tsubst_aggr_type. Doing so causes us to ICE on template/nested5.C
> > > because during lookup_template_class for A<T>::C::D<S> with T=E and S=S,
> > > we substitute and complete the context A<T>::C with T=E, which in turn
> > > registers the desired dependent specialization of D for us and we end up
> > > trying to register it again. This patch fixes this by checking the
> > > specializations table again after completion of the context.
> > >
> > > This patch also implements a couple of other optimizations:
> > >
> > > * In lookup_template_class, if the context of the partially
> > > instantiated template is already non-dependent, then we could
> > > reuse that instead of substituting the context of the most
> > > general template.
> > > * When substituting the TYPE_DECL for an injected-class-name
> > > in tsubst_decl, we can avoid substituting its TREE_TYPE and
> > > DECL_TI_ARGS.
> > >
> > > Together these optimizations improve memory usage for the range-v3
> > > testcase test/view/split.cc by about 5%. The improvement is probably
> > > more significant when dealing with deeply nested class templates.
> > >
> > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > > trunk?
> > >
> > > gcc/cp/ChangeLog:
> > >
> > > * pt.cc (lookup_template_class): Remove dead stores to
> > > context parameter. Don't substitute the context of the
> > > most general template if that of the partially instantiated
> > > template is non-dependent. Check the specializations table
> > > again after completing the context of a nested dependent
> > > specialization.
> > > (tsubst_aggr_type) <case RECORD_TYPE>: Don't substitute
> > > TYPE_CONTEXT or pass it to lookup_template_class.
> > > (tsubst_decl) <case TYPE_DECL>: Avoid substituting the
> > > TREE_TYPE and DECL_TI_ARGS when DECL_SELF_REFERENCE_P.
> > > ---
> > > gcc/cp/pt.cc | 69 +++++++++++++++++++++++++++++++---------------------
> > > 1 file changed, 41 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > > index 59b94317e88..28023d60684 100644
> > > --- a/gcc/cp/pt.cc
> > > +++ b/gcc/cp/pt.cc
> > > @@ -9840,8 +9840,6 @@ lookup_template_class (tree d1, tree arglist, tree
> > > in_decl, tree context,
> > > if (context)
> > > pop_decl_namespace ();
> > > }
> > > - if (templ)
> > > - context = DECL_CONTEXT (templ);
> > > }
> > > else if (TREE_CODE (d1) == TYPE_DECL && MAYBE_CLASS_TYPE_P (TREE_TYPE
> > > (d1)))
> > > {
> > > @@ -9868,7 +9866,6 @@ lookup_template_class (tree d1, tree arglist, tree
> > > in_decl, tree context,
> > > {
> > > templ = d1;
> > > d1 = DECL_NAME (templ);
> > > - context = DECL_CONTEXT (templ);
> > > }
> > > else if (DECL_TEMPLATE_TEMPLATE_PARM_P (d1))
> > > {
> > > @@ -10059,8 +10056,25 @@ lookup_template_class (tree d1, tree arglist,
> > > tree
> > > in_decl, tree context,
> > > context = DECL_CONTEXT (gen_tmpl);
> > > if (context && TYPE_P (context))
> > > {
> > > - context = tsubst_aggr_type (context, arglist, complain, in_decl,
> > > true);
> > > - context = complete_type (context);
> > > + if (!uses_template_parms (DECL_CONTEXT (templ)))
> > > + /* If the context of the partially instantiated template is
> > > + already non-dependent, then we might as well use it. */
> > > + context = DECL_CONTEXT (templ);
> > > + else
> > > + {
> > > + context = tsubst_aggr_type (context, arglist, complain, in_decl,
> > > true);
> > > + context = complete_type (context);
> > > + if (is_dependent_type && arg_depth > 1)
> > > + {
> > > + /* If this is a dependent nested specialization such as
> > > + A<int>::B<T>, then completion of A<int> might have
> > > + registered this specialization of B for us, so check
> > > + the table again (33959). */
> > > + entry = type_specializations->find_with_hash (&elt, hash);
> > > + if (entry)
> > > + return entry->spec;
> > > + }
> > > + }
> > > }
> > > else
> > > context = tsubst (context, arglist, complain, in_decl);
> > > @@ -13711,25 +13725,12 @@ tsubst_aggr_type (tree t,
> > > if (TYPE_TEMPLATE_INFO (t) && uses_template_parms (t))
> > > {
> > > tree argvec;
> > > - tree context;
> > > tree r;
> > > /* In "sizeof(X<I>)" we need to evaluate "I". */
> > > cp_evaluated ev;
> > > - /* First, determine the context for the type we are looking
> > > - up. */
> > > - context = TYPE_CONTEXT (t);
> > > - if (context && TYPE_P (context))
> > > - {
> > > - context = tsubst_aggr_type (context, args, complain,
> > > - in_decl, /*entering_scope=*/1);
> > > - /* If context is a nested class inside a class template,
> > > - it may still need to be instantiated (c++/33959). */
> > > - context = complete_type (context);
> > > - }
> > > -
> > > - /* Then, figure out what arguments are appropriate for the
> > > + /* Figure out what arguments are appropriate for the
> > > type we are trying to find. For example, given:
> > > template <class T> struct S;
> > > @@ -13744,7 +13745,7 @@ tsubst_aggr_type (tree t,
> > > r = error_mark_node;
> > > else
> > > {
> > > - r = lookup_template_class (t, argvec, in_decl, context,
> > > + r = lookup_template_class (t, argvec, in_decl, NULL_TREE,
> > > entering_scope, complain);
> > > r = cp_build_qualified_type (r, cp_type_quals (t),
> > > complain);
> > > }
> > > @@ -14880,6 +14881,10 @@ tsubst_decl (tree t, tree args, tsubst_flags_t
> > > complain)
> > > ctx = tsubst_aggr_type (ctx, args,
> > > complain,
> > > in_decl, /*entering_scope=*/1);
> > > + if (DECL_SELF_REFERENCE_P (t))
> > > + /* The context and type of a injected-class-name are
> > > + the same, so we don't need to substitute both. */
> > > + type = ctx;
> > > /* If CTX is unchanged, then T is in fact the
> > > specialization we want. That situation occurs when
> > > referencing a static data member within in its own
> > > @@ -14900,14 +14905,22 @@ tsubst_decl (tree t, tree args, tsubst_flags_t
> > > complain)
> > > {
> > > tmpl = DECL_TI_TEMPLATE (t);
> > > gen_tmpl = most_general_template (tmpl);
> > > - argvec = tsubst (DECL_TI_ARGS (t), args, complain, in_decl);
> > > - if (argvec != error_mark_node)
> > > - argvec = (coerce_innermost_template_parms
> > > - (DECL_TEMPLATE_PARMS (gen_tmpl),
> > > - argvec, t, complain,
> > > - /*all*/true, /*defarg*/true));
> > > - if (argvec == error_mark_node)
> > > - RETURN (error_mark_node);
> > > + if (DECL_SELF_REFERENCE_P (t))
> > > + /* The DECL_TI_ARGS for the injected-class-name are the
> > > + generic template arguments for the class template, so
> > > + substitution/coercion is just the identity mapping. */
> > > + argvec = args;
> >
> > Would it make sense to extend this to any TEMPLATE_DECL for which
> > DECL_PRIMARY_TEMPLATE is the class template? So, anything that gets here
> > except an alias template.
>
> Ah nice, it does look like we could extend this to any TEMPLATE_DECL that
> satisfies DECL_CLASS_SCOPE_P && !DECL_MEMBER_TEMPLATE_P (so that we also
> exclude static data member templates), i.e. any templated non-template
> member. Is that equivalent to what you had in mind?
>
> Based on some light testing, if we do this, it seems we also need to
> handle 'args' having greater depth than 'DECL_TI_ARGS' here, something
> which could happen during satisfaction.
... or we could just restrict the optimization to when the argument
depths match, like so:
-- >8 --
Subject: [PATCH] c++: optimize specialization of nested templated classes
gcc/cp/ChangeLog:
* pt.cc (lookup_template_class): Remove dead stores to
context parameter. Don't substitute the context of the
most general template if that of the partially instantiated
template is non-dependent. Check the specializations table
again after completing the context of a nested dependent
specialization.
(tsubst_aggr_type) <case RECORD_TYPE>: Don't substitute
TYPE_CONTEXT or pass it to lookup_template_class.
(tsubst_decl) <case TYPE_DECL>: Avoid substituting the
TREE_TYPE and DECL_TI_ARGS when DECL_SELF_REFERENCE_P.
---
gcc/cp/pt.cc | 73 ++++++++++++++++++++++++++++++++--------------------
1 file changed, 45 insertions(+), 28 deletions(-)
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 3154186ac20..ebd822373db 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -9840,8 +9840,6 @@ lookup_template_class (tree d1, tree arglist, tree
in_decl, tree context,
if (context)
pop_decl_namespace ();
}
- if (templ)
- context = DECL_CONTEXT (templ);
}
else if (TREE_CODE (d1) == TYPE_DECL && MAYBE_CLASS_TYPE_P (TREE_TYPE (d1)))
{
@@ -9868,7 +9866,6 @@ lookup_template_class (tree d1, tree arglist, tree
in_decl, tree context,
{
templ = d1;
d1 = DECL_NAME (templ);
- context = DECL_CONTEXT (templ);
}
else if (DECL_TEMPLATE_TEMPLATE_PARM_P (d1))
{
@@ -10059,8 +10056,26 @@ lookup_template_class (tree d1, tree arglist, tree
in_decl, tree context,
context = DECL_CONTEXT (gen_tmpl);
if (context && TYPE_P (context))
{
- context = tsubst_aggr_type (context, arglist, complain, in_decl,
true);
- context = complete_type (context);
+ if (!uses_template_parms (DECL_CONTEXT (templ)))
+ /* If the context of the partially instantiated template is
+ already non-dependent, then we might as well use it. */
+ context = DECL_CONTEXT (templ);
+ else
+ {
+ context = tsubst_aggr_type (context, arglist,
+ complain, in_decl, true);
+ context = complete_type (context);
+ if (is_dependent_type && arg_depth > 1)
+ {
+ /* If this is a dependent nested specialization such as
+ A<int>::B<T>, then completion of A<int> might have
+ registered this specialization of B for us, so check
+ the table again (33959). */
+ entry = type_specializations->find_with_hash (&elt, hash);
+ if (entry)
+ return entry->spec;
+ }
+ }
}
else
context = tsubst (context, arglist, complain, in_decl);
@@ -13739,25 +13754,12 @@ tsubst_aggr_type (tree t,
if (TYPE_TEMPLATE_INFO (t) && uses_template_parms (t))
{
tree argvec;
- tree context;
tree r;
/* In "sizeof(X<I>)" we need to evaluate "I". */
cp_evaluated ev;
- /* First, determine the context for the type we are looking
- up. */
- context = TYPE_CONTEXT (t);
- if (context && TYPE_P (context))
- {
- context = tsubst_aggr_type (context, args, complain,
- in_decl, /*entering_scope=*/1);
- /* If context is a nested class inside a class template,
- it may still need to be instantiated (c++/33959). */
- context = complete_type (context);
- }
-
- /* Then, figure out what arguments are appropriate for the
+ /* Figure out what arguments are appropriate for the
type we are trying to find. For example, given:
template <class T> struct S;
@@ -13772,7 +13774,7 @@ tsubst_aggr_type (tree t,
r = error_mark_node;
else
{
- r = lookup_template_class (t, argvec, in_decl, context,
+ r = lookup_template_class (t, argvec, in_decl, NULL_TREE,
entering_scope, complain);
r = cp_build_qualified_type (r, cp_type_quals (t), complain);
}
@@ -14913,6 +14915,10 @@ tsubst_decl (tree t, tree args, tsubst_flags_t
complain)
ctx = tsubst_aggr_type (ctx, args,
complain,
in_decl, /*entering_scope=*/1);
+ if (DECL_SELF_REFERENCE_P (t))
+ /* The context and type of an injected-class-name are
+ the same, so we don't need to substitute both. */
+ type = ctx;
/* If CTX is unchanged, then T is in fact the
specialization we want. That situation occurs when
referencing a static data member within in its own
@@ -14933,14 +14939,25 @@ tsubst_decl (tree t, tree args, tsubst_flags_t
complain)
{
tmpl = DECL_TI_TEMPLATE (t);
gen_tmpl = most_general_template (tmpl);
- argvec = tsubst (DECL_TI_ARGS (t), args, complain, in_decl);
- if (argvec != error_mark_node)
- argvec = (coerce_innermost_template_parms
- (DECL_TEMPLATE_PARMS (gen_tmpl),
- argvec, t, complain,
- /*all*/true, /*defarg*/true));
- if (argvec == error_mark_node)
- RETURN (error_mark_node);
+ if (DECL_CLASS_SCOPE_P (tmpl)
+ && !DECL_MEMBER_TEMPLATE_P (tmpl)
+ && (TMPL_ARGS_DEPTH (args)
+ == TMPL_ARGS_DEPTH (DECL_TI_ARGS (t))))
+ /* The DECL_TI_ARGS in this case are the generic template
+ arguments for the class template, so substitution/coercion
+ is just the identity mapping. */
+ argvec = args;
+ else
+ {
+ argvec = tsubst (DECL_TI_ARGS (t), args, complain, in_decl);
+ if (argvec != error_mark_node)
+ argvec = (coerce_innermost_template_parms
+ (DECL_TEMPLATE_PARMS (gen_tmpl),
+ argvec, t, complain,
+ /*all*/true, /*defarg*/true));
+ if (argvec == error_mark_node)
+ RETURN (error_mark_node);
+ }
hash = hash_tmpl_and_args (gen_tmpl, argvec);
spec = retrieve_specialization (gen_tmpl, argvec, hash);
}
--
2.36.1.363.g9c897eef06
