From: Patrick Palka <ppalka@redhat.com>
To: Patrick Palka <ppalka@redhat.com>
Cc: Jason Merrill <jason@redhat.com>, gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] c++: generic targs and identity substitution [PR105956]
Date: Thu, 7 Jul 2022 13:15:42 -0400 (EDT) [thread overview]
Message-ID: <0338486e-a85b-9501-cd80-54a96154be1d@idea> (raw)
In-Reply-To: <af1f46b4-982a-3ec1-b1fa-e945f11492d5@idea>
On Thu, 7 Jul 2022, Patrick Palka wrote:
> On Thu, 7 Jul 2022, Jason Merrill wrote:
>
> > On 7/6/22 15:26, Patrick Palka wrote:
> > > On Tue, 5 Jul 2022, Jason Merrill wrote:
> > >
> > > > On 7/5/22 10:06, Patrick Palka wrote:
> > > > > On Fri, 1 Jul 2022, Jason Merrill wrote:
> > > > >
> > > > > > On 6/29/22 13:42, Patrick Palka wrote:
> > > > > > > In r13-1045-gcb7fd1ea85feea I assumed that substitution into generic
> > > > > > > DECL_TI_ARGS corresponds to an identity mapping of the given
> > > > > > > arguments,
> > > > > > > and hence its safe to always elide such substitution. But this PR
> > > > > > > demonstrates that such a substitution isn't always the identity
> > > > > > > mapping,
> > > > > > > in particular when there's an ARGUMENT_PACK_SELECT argument, which
> > > > > > > gets
> > > > > > > handled specially during substitution:
> > > > > > >
> > > > > > > * when substituting an APS into a template parameter, we strip
> > > > > > > the
> > > > > > > APS to its underlying argument;
> > > > > > > * and when substituting an APS into a pack expansion, we strip
> > > > > > > the
> > > > > > > APS to its underlying argument pack.
> > > > > >
> > > > > > Ah, right. For instance, in variadic96.C we have
> > > > > >
> > > > > > 10 template < typename... T >
> > > > > > 11 struct derived
> > > > > > 12 : public base< T, derived< T... > >...
> > > > > >
> > > > > > so when substituting into the base-specifier, we're approaching it
> > > > > > from
> > > > > > the
> > > > > > outside in, so when we get to the inner T... we need some way to find
> > > > > > the
> > > > > > T
> > > > > > pack again. It might be possible to remove the need for APS by
> > > > > > substituting
> > > > > > inner pack expansions before outer ones, which could improve
> > > > > > worst-case
> > > > > > complexity, but I don't know how relevant that is in real code; I
> > > > > > imagine
> > > > > > most
> > > > > > inner pack expansions are as simple as this one.
> > > > >
> > > > > Aha, that makes sense.
> > > > >
> > > > > >
> > > > > > > In this testcase, when expanding the pack expansion pattern (idx +
> > > > > > > Ns)...
> > > > > > > with Ns={0,1}, we specialize idx twice, first with Ns=APS<0,{0,1}>
> > > > > > > and
> > > > > > > then Ns=APS<1,{0,1}>. The DECL_TI_ARGS of idx are the generic
> > > > > > > template
> > > > > > > arguments of the enclosing class template impl, so before r13-1045,
> > > > > > > we'd substitute into its DECL_TI_ARGS which gave Ns={0,1} as
> > > > > > > desired.
> > > > > > > But after r13-1045, we elide this substitution and end up attempting
> > > > > > > to
> > > > > > > hash the original Ns argument, an APS, which ICEs.
> > > > > > >
> > > > > > > So this patch partially reverts this part of r13-1045. I considered
> > > > > > > using preserve_args in this case instead, but that'd break the
> > > > > > > static_assert in the testcase because preserve_args always strips
> > > > > > > APS to
> > > > > > > its underlying argument, but here we want to strip it to its
> > > > > > > underlying
> > > > > > > argument pack, so we'd incorrectly end up forming the
> > > > > > > specializations
> > > > > > > impl<0>::idx and impl<1>::idx instead of impl<0,1>::idx.
> > > > > > >
> > > > > > > Although we can't elide the substitution into DECL_TI_ARGS in light
> > > > > > > of
> > > > > > > ARGUMENT_PACK_SELECT, it should still be safe to elide template
> > > > > > > argument
> > > > > > > coercion in the case of a non-template decl, which this patch
> > > > > > > preserves.
> > > > > > >
> > > > > > > It's unfortunate that we need to remove this optimization just
> > > > > > > because
> > > > > > > it doesn't hold for one special tree code. So this patch implements
> > > > > > > a
> > > > > > > heuristic in tsubst_template_args to avoid allocating a new TREE_VEC
> > > > > > > if
> > > > > > > the substituted elements are identical to those of a level from
> > > > > > > ARGS.
> > > > > > > It turns out that about 30% of all calls to tsubst_template_args
> > > > > > > benefit
> > > > > > > from this optimization, and it reduces memory usage by about 1.5%
> > > > > > > for
> > > > > > > e.g. stdc++.h (relative to r13-1045). (This is the maybe_reuse
> > > > > > > stuff,
> > > > > > > the rest of the changes to tsubst_template_args are just drive-by
> > > > > > > cleanups.)
> > > > > > >
> > > > > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> > > > > > > for
> > > > > > > trunk? Patch generated with -w to ignore noisy whitespace changes.
> > > > > > >
> > > > > > > PR c++/105956
> > > > > > >
> > > > > > > gcc/cp/ChangeLog:
> > > > > > >
> > > > > > > * pt.cc (tsubst_template_args): Move variable declarations
> > > > > > > closer to their first use. Replace 'orig_t' with 'r'. Rename
> > > > > > > 'need_new' to 'const_subst_p'. Heuristically detect if the
> > > > > > > substituted elements are identical to that of a level from
> > > > > > > 'args' and avoid allocating a new TREE_VEC if so.
> > > > > > > (tsubst_decl) <case TYPE_DECL, case VAR_DECL>: Revert
> > > > > > > r13-1045-gcb7fd1ea85feea change for avoiding substitution into
> > > > > > > DECL_TI_ARGS, but still avoid coercion in this case.
> > > > > > >
> > > > > > > gcc/testsuite/ChangeLog:
> > > > > > >
> > > > > > > * g++.dg/cpp0x/variadic183.C: New test.
> > > > > > > ---
> > > > > > > gcc/cp/pt.cc | 113
> > > > > > > ++++++++++++++---------
> > > > > > > gcc/testsuite/g++.dg/cpp0x/variadic183.C | 14 +++
> > > > > > > 2 files changed, 85 insertions(+), 42 deletions(-)
> > > > > > > create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic183.C
> > > > > > >
> > > > > > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > > > > > > index 8672da123f4..7898834faa6 100644
> > > > > > > --- a/gcc/cp/pt.cc
> > > > > > > +++ b/gcc/cp/pt.cc
> > > > > > > @@ -27,6 +27,7 @@ along with GCC; see the file COPYING3. If not see
> > > > > > > Fixed by: C++20 modules. */
> > > > > > > #include "config.h"
> > > > > > > +#define INCLUDE_ALGORITHM // for std::equal
> > > > > > > #include "system.h"
> > > > > > > #include "coretypes.h"
> > > > > > > #include "cp-tree.h"
> > > > > > > @@ -13544,17 +13545,22 @@ tsubst_argument_pack (tree orig_arg, tree
> > > > > > > args,
> > > > > > > tsubst_flags_t complain,
> > > > > > > tree
> > > > > > > tsubst_template_args (tree t, tree args, tsubst_flags_t
> > > > > > > complain,
> > > > > > > tree
> > > > > > > in_decl)
> > > > > > > {
> > > > > > > - tree orig_t = t;
> > > > > > > - int len, need_new = 0, i, expanded_len_adjust = 0, out;
> > > > > > > - tree *elts;
> > > > > > > -
> > > > > > > if (t == error_mark_node)
> > > > > > > return error_mark_node;
> > > > > > > - len = TREE_VEC_LENGTH (t);
> > > > > > > - elts = XALLOCAVEC (tree, len);
> > > > > > > + const int len = TREE_VEC_LENGTH (t);
> > > > > > > + tree *elts = XALLOCAVEC (tree, len);
> > > > > > > + int expanded_len_adjust = 0;
> > > > > > > - for (i = 0; i < len; i++)
> > > > > > > + /* True iff no element of T was changed by the substitution. */
> > > > > > > + bool const_subst_p = true;
> > > > > > > +
> > > > > > > + /* If MAYBE_REUSE is non-NULL, as an optimization we'll try to
> > > > > > > reuse
> > > > > > > and
> > > > > > > + return this TREE_VEC instead of allocating a new one if
> > > > > > > possible.
> > > > > > > This
> > > > > > > + will either be ARGS or a level from ARGS. */
> > > > > > > + tree maybe_reuse = NULL_TREE;
> > > > > > > +
> > > > > > > + for (int i = 0; i < len; i++)
> > > > > > > {
> > > > > > > tree orig_arg = TREE_VEC_ELT (t, i);
> > > > > > > tree new_arg;
> > > > > > > @@ -13580,56 +13586,90 @@ tsubst_template_args (tree t, tree args,
> > > > > > > tsubst_flags_t complain, tree in_decl)
> > > > > > > else if (ARGUMENT_PACK_P (orig_arg))
> > > > > > > new_arg = tsubst_argument_pack (orig_arg, args, complain,
> > > > > > > in_decl);
> > > > > > > else
> > > > > > > + {
> > > > > > > new_arg = tsubst_template_arg (orig_arg, args, complain,
> > > > > > > in_decl);
> > > > > > > + /* If T heuristically appears to be a set of generic
> > > > > > > template
> > > > > > > + arguments, set MAYBE_REUSE to the corresponding level
> > > > > > > from
> > > > > > > + ARGS. */
> > > > > > > + if (maybe_reuse == NULL_TREE && orig_arg != NULL_TREE)
> > > > > > > + {
> > > > > > > + if (TEMPLATE_PARM_P (orig_arg))
> > > > > > > + {
> > > > > >
> > > > > > This doesn't handle the case of variadic template parameters, which
> > > > > > are
> > > > > > represented in the generic args with a pack expansion. If this is a
> > > > > > choice,
> > > > > > there should be a comment about it.
> > > > >
> > > > > AFAICT substituting such a pack expansion will never be an identity
> > > > > transform -- the relevant targ during tsubst_pack_expansion will be an
> > > > > ARGUMENT_PACK, and we'll return the TREE_VEC from that ARGUMENT_PACK
> > > > > instead of the ARGUMENT_PACK itself, so there's no way we can reuse (a
> > > > > level from) 'args' in this case.
> > > >
> > > > Hmm, when replacing a level of T... we start with a TREE_VEC containing an
> > > > ARGUMENT_PACK around a TREE_VEC containing a PACK_EXPANSION, and
> > > > substitution
> > > > should replace that with the argument level, a TREE_VEC containing an
> > > > ARGUMENT_PACK around a TREE_VEC containing an actual set of args, so reuse
> > > > ought to be possible?
> > >
> > > Ah, I think see what you mean. For that, I think it suffices to just
> > > handle in tsubst_template_args the case where we're substituting into a
> > > single-elt TREE_VEC such as {T...}. That'll allow us to reuse the inner
> > > TREE_VEC containing the actual set of args at least.
> >
> > Sounds good.
> >
> > > And AFAICT that's
> > > the best we can do, since we'll always be creating a new ARGUMENT_PACK
> > > which doesn't appear in any other TREE_VEC we have at our disposal.
> >
> > Why always? Why can't tsubst_argument_pack recognize the {T...} case and
> > return the corresponding ARGUMENT_PACK from args?
> >
> > template <class... Ts> struct A
> > {
> > A<Ts...>* a;
> > };
> >
> > A<int,char> a;
> >
> > With your patch, the substitution into A<Ts...> reuses the inner TREE_VEC, but
> > why not reuse the ARGUMENT_PACK as well? And why not set maybe_reuse for the
> > enclosing arg level?
>
> D'oh, you're totally right, I didn't notice this opportunity. Here's a
> patch that makes tsubst_argument_pack reuse the ARGUMENT_PACK from
> 'args' when possible, and in turn makes tsubst_template_args reuse the
> enclosing arg level. Relative to the previous patch, this increases
> the % of calls to tsubst_template_args that benefit from this
> optimization a further 10% (30% -> 40%), and reduces memory usage for
> e.g. zip.cpp from range-v3 a further 2.5% (1.5% -> 4%).
>
> -- >8 --
>
> Subject: [PATCH] c++: generic targs and identity substitution [PR105956]
>
> In r13-1045-gcb7fd1ea85feea I assumed that substitution into generic
> DECL_TI_ARGS corresponds to an identity mapping of the given arguments,
> and hence its safe to always elide such substitution. But this PR
> demonstrates that such a substitution isn't always the identity mapping,
> in particular when there's an ARGUMENT_PACK_SELECT argument, which gets
> handled specially during substitution:
>
> * when substituting an APS into a template parameter, we strip the
> APS to its underlying argument;
> * and when substituting an APS into a pack expansion, we strip the
> APS to its underlying argument pack.
>
> In this testcase, when expanding the pack expansion pattern (idx + Ns)...
> with Ns={0,1}, we specialize idx twice, first with Ns=APS<0,{0,1}> and
> then Ns=APS<1,{0,1}>. The DECL_TI_ARGS of idx are the generic template
> arguments of the enclosing class template impl, so before r13-1045,
> we'd substitute into its DECL_TI_ARGS which gave Ns={0,1} as desired.
> But after r13-1045, we elide this substitution and end up attempting to
> hash the original Ns argument, an APS, which ICEs.
>
> So this patch reverts that part of r13-1045. I considered using
> preserve_args in this case instead, but that'd break the static_assert
> in the testcase because preserve_args always strips APS to its
> underlying argument, but here we want to strip it to its underlying
> argument pack, so we'd incorrectly end up forming the specializations
> impl<0>::idx and impl<1>::idx instead of impl<0,1>::idx.
>
> Although we can't elide the substitution into DECL_TI_ARGS in light of
> ARGUMENT_PACK_SELECT, it should still be safe to elide template argument
> coercion in the case of a non-template decl, which this patch preserves.
>
> It's unfortunate that we need to remove this optimization just because
> it doesn't hold for one special tree code. So this patch implements a
> heuristic in tsubst_template_args to avoid allocating a new TREE_VEC if
> the substituted elements are identical to those of a level from ARGS,
> and a similar heuristic for tsubst_argument_pack. It turns out that
> about 40% of all calls to tsubst_template_args benefit from this, and it
> reduces memory usage by about 4% for e.g. zip.cpp from range-v3 (relative
> to r13-1045) which more than makes up for the reversion.
>
> PR c++/105956
>
> gcc/cp/ChangeLog:
>
> * pt.cc (template_arg_to_parm): Define.
> (tsubst_argument_pack): Try to reuse the corresponding
> ARGUMENT_PACK from 'args' when substituting into an
> ARGUMENT_PACK for a generic template argument.
> (tsubst_template_args): Move variable declarations
> closer to their first use. Replace 'orig_t' with 'r'. Rename
> 'need_new' to 'const_subst_p'. Heuristically detect if the
> substituted elements are identical to that of a level from
> 'args' and avoid allocating a new TREE_VEC if so. Assert that
> 'out' never exceeds the length of the new TREE_VEC, and remove
> dead ARGUMENT_PACK_P test.
> (tsubst_decl) <case TYPE_DECL, case VAR_DECL>: Revert
> r13-1045-gcb7fd1ea85feea change for avoiding substitution into
> DECL_TI_ARGS, but still avoid coercion in this case.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp0x/variadic183.C: New test.
> ---
> gcc/cp/pt.cc | 172 ++++++++++++++++-------
> gcc/testsuite/g++.dg/cpp0x/variadic183.C | 14 ++
> 2 files changed, 138 insertions(+), 48 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic183.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 8672da123f4..85f3462a0ac 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -27,6 +27,7 @@ along with GCC; see the file COPYING3. If not see
> Fixed by: C++20 modules. */
>
> #include "config.h"
> +#define INCLUDE_ALGORITHM // for std::equal
> #include "system.h"
> #include "coretypes.h"
> #include "cp-tree.h"
> @@ -4916,6 +4917,33 @@ template_parm_to_arg (tree t)
> return t;
> }
>
> +/* If T looks like a generic template argument produced by template_parm_to_arg,
> + return the corresponding template parameter, otherwise return NULL_TREE. */
> +
> +static tree
> +template_arg_to_parm (tree t)
> +{
> + if (t == NULL_TREE)
> + return NULL_TREE;
> +
> + if (ARGUMENT_PACK_P (t))
> + {
> + tree args = ARGUMENT_PACK_ARGS (t);
> + if (TREE_VEC_LENGTH (args) == 1
> + && PACK_EXPANSION_P (TREE_VEC_ELT (args, 0)))
> + {
> + t = PACK_EXPANSION_PATTERN (TREE_VEC_ELT (args, 0));
> + if (REFERENCE_REF_P (t))
> + t = TREE_OPERAND (t, 0);
Whoops, we should look through REFERENCE_REF_P even in the non-variadic
case to more closely mirror template_parm_to_arg, consider that fixed.
> + }
> + }
> +
> + if (TEMPLATE_PARM_P (t))
> + return t;
> +
> + return NULL_TREE;
> +}
> +
> /* Given a single level of template parameters (a TREE_VEC), return it
> as a set of template arguments. */
>
> @@ -13516,12 +13544,38 @@ tree
> tsubst_argument_pack (tree orig_arg, tree args, tsubst_flags_t complain,
> tree in_decl)
> {
> + /* This flag is used only during deduction, and we don't expect to
> + see such ARGUMENT_PACKs during substitution. */
> + gcc_assert (!ARGUMENT_PACK_INCOMPLETE_P (orig_arg));
> +
> /* Substitute into each of the arguments. */
> tree pack_args = tsubst_template_args (ARGUMENT_PACK_ARGS (orig_arg),
> args, complain, in_decl);
> - tree new_arg = error_mark_node;
> - if (pack_args != error_mark_node)
> + if (pack_args == error_mark_node)
> + return error_mark_node;
> +
> + if (pack_args == ARGUMENT_PACK_ARGS (orig_arg))
> + return orig_arg;
> +
> + /* If we're substituting into an ARGUMENT_PACK for a generic template
> + argument, we might be able to avoid allocating a new ARGUMENT_PACK
> + by reusing the corresponding ARGUMENT_PACK from ARGS if the
> + substituted result is identical to it. */
> + if (tree parm = template_arg_to_parm (orig_arg))
> {
> + int level, index;
> + template_parm_level_and_index (parm, &level, &index);
> + if (TMPL_ARGS_DEPTH (args) >= level)
> + if (tree arg = TMPL_ARG (args, level, index))
> + if (TREE_CODE (arg) == TREE_CODE (orig_arg)
> + && ARGUMENT_PACK_ARGS (arg) == pack_args)
> + {
> + gcc_assert (!ARGUMENT_PACK_INCOMPLETE_P (arg));
> + return arg;
> + }
> + }
> +
> + tree new_arg;
> if (TYPE_P (orig_arg))
> {
> new_arg = cxx_make_type (TREE_CODE (orig_arg));
> @@ -13532,10 +13586,7 @@ tsubst_argument_pack (tree orig_arg, tree args, tsubst_flags_t complain,
> new_arg = make_node (TREE_CODE (orig_arg));
> TREE_CONSTANT (new_arg) = TREE_CONSTANT (orig_arg);
> }
> -
> ARGUMENT_PACK_ARGS (new_arg) = pack_args;
> - }
> -
> return new_arg;
> }
>
> @@ -13544,17 +13595,22 @@ tsubst_argument_pack (tree orig_arg, tree args, tsubst_flags_t complain,
> tree
> tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl)
> {
> - tree orig_t = t;
> - int len, need_new = 0, i, expanded_len_adjust = 0, out;
> - tree *elts;
> -
> if (t == error_mark_node)
> return error_mark_node;
>
> - len = TREE_VEC_LENGTH (t);
> - elts = XALLOCAVEC (tree, len);
> + const int len = TREE_VEC_LENGTH (t);
> + tree *elts = XALLOCAVEC (tree, len);
> + int expanded_len_adjust = 0;
>
> - for (i = 0; i < len; i++)
> + /* True iff the substituted result is identical to T. */
> + bool const_subst_p = true;
> +
> + /* If MAYBE_REUSE is a TREE_VEC, as an optimization we'll try to reuse and
> + return this TREE_VEC instead of allocating a new one if possible. This
> + will either be ARGS or a level from ARGS. */
> + tree maybe_reuse = NULL_TREE;
> +
> + for (int i = 0; i < len; i++)
> {
> tree orig_arg = TREE_VEC_ELT (t, i);
> tree new_arg;
> @@ -13587,49 +13643,80 @@ tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl)
>
> elts[i] = new_arg;
> if (new_arg != orig_arg)
> - need_new = 1;
> + const_subst_p = false;
> }
>
> - if (!need_new)
> + if (const_subst_p)
> return t;
>
> + /* If T appears to be a set of generic template arguments, set
> + MAYBE_REUSE to the corresponding level from ARGS. */
> + if (tree parm = template_arg_to_parm (TREE_VEC_ELT (t, 0)))
> + {
> + int level, index;
> + template_parm_level_and_index (parm, &level, &index);
> + if (index == 0 && TMPL_ARGS_DEPTH (args) >= level)
> + maybe_reuse = TMPL_ARGS_LEVEL (args, level);
> + }
> + /* If ARGS and T are both multi-level, the substituted result may be
> + identical to ARGS (if each level was pairwise identical). */
> + else if (TMPL_ARGS_HAVE_MULTIPLE_LEVELS (t)
> + && TMPL_ARGS_HAVE_MULTIPLE_LEVELS (args))
> + maybe_reuse = args;
> +
> + /* Return MAYBE_REUSE and avoid allocating a new TREE_VEC if the substituted
> + result is identical to it. */
> + if (maybe_reuse != NULL_TREE
> + && TREE_VEC_LENGTH (maybe_reuse) == len
> + && std::equal (elts, elts+len, TREE_VEC_BEGIN (maybe_reuse)))
> + return maybe_reuse;
> +
> + /* If T consists of only a pack expansion for which substitution yielded
> + a TREE_VEC of the expanded elements, then reuse that TREE_VEC instead
> + of effectively making a copy. */
> + if (len == 1
> + && PACK_EXPANSION_P (TREE_VEC_ELT (t, 0))
> + && TREE_CODE (elts[0]) == TREE_VEC)
> + return elts[0];
> +
> /* Make space for the expanded arguments coming from template
> argument packs. */
> - t = make_tree_vec (len + expanded_len_adjust);
> - /* ORIG_T can contain TREE_VECs. That happens if ORIG_T contains the
> + tree r = make_tree_vec (len + expanded_len_adjust);
> + /* T can contain TREE_VECs. That happens if T contains the
> arguments for a member template.
> - In that case each TREE_VEC in ORIG_T represents a level of template
> - arguments, and ORIG_T won't carry any non defaulted argument count.
> + In that case each TREE_VEC in T represents a level of template
> + arguments, and T won't carry any non defaulted argument count.
> It will rather be the nested TREE_VECs that will carry one.
> - In other words, ORIG_T carries a non defaulted argument count only
> + In other words, T carries a non defaulted argument count only
> if it doesn't contain any nested TREE_VEC. */
> - if (NON_DEFAULT_TEMPLATE_ARGS_COUNT (orig_t))
> + if (NON_DEFAULT_TEMPLATE_ARGS_COUNT (t))
> {
> - int count = GET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (orig_t);
> + int count = GET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (t);
> count += expanded_len_adjust;
> - SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (t, count);
> + SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (r, count);
> }
> - for (i = 0, out = 0; i < len; i++)
> +
> + int out = 0;
> + for (int i = 0; i < len; i++)
> {
> - tree orig_arg = TREE_VEC_ELT (orig_t, i);
> + tree orig_arg = TREE_VEC_ELT (t, i);
> if (orig_arg
> - && (PACK_EXPANSION_P (orig_arg) || ARGUMENT_PACK_P (orig_arg))
> + && PACK_EXPANSION_P (orig_arg)
> && TREE_CODE (elts[i]) == TREE_VEC)
> {
> - int idx;
> -
> /* Now expand the template argument pack "in place". */
> - for (idx = 0; idx < TREE_VEC_LENGTH (elts[i]); idx++, out++)
> - TREE_VEC_ELT (t, out) = TREE_VEC_ELT (elts[i], idx);
> + for (int idx = 0; idx < TREE_VEC_LENGTH (elts[i]); idx++, out++)
> + TREE_VEC_ELT (r, out) = TREE_VEC_ELT (elts[i], idx);
> }
> else
> {
> - TREE_VEC_ELT (t, out) = elts[i];
> + TREE_VEC_ELT (r, out) = elts[i];
> out++;
> }
> }
> + gcc_assert (out <= TREE_VEC_LENGTH (r));
And I think this could be strengthed to ==.
>
> - return t;
> + return r;
> }
>
> /* Substitute ARGS into one level PARMS of template parameters. */
> @@ -14965,32 +15052,21 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
>
> if (!spec)
> {
> - int args_depth = TMPL_ARGS_DEPTH (args);
> - int parms_depth = TMPL_ARGS_DEPTH (DECL_TI_ARGS (t));
> tmpl = DECL_TI_TEMPLATE (t);
> gen_tmpl = most_general_template (tmpl);
> - if (args_depth == parms_depth
> - && !PRIMARY_TEMPLATE_P (gen_tmpl))
> - /* The DECL_TI_ARGS in this case are the generic template
> - arguments for the enclosing class template, so we can
> - shortcut substitution (which would just be the identity
> - mapping). */
> - argvec = args;
> - else
> - {
> argvec = tsubst (DECL_TI_ARGS (t), args, complain, in_decl);
> - /* Coerce the innermost arguments again if necessary. If
> - there's fewer levels of args than of parms, then the
> - substitution could not have changed the innermost args
> - (modulo level lowering). */
> - if (args_depth >= parms_depth && argvec != error_mark_node)
> + if (argvec != error_mark_node
> + && PRIMARY_TEMPLATE_P (gen_tmpl)
> + && TMPL_ARGS_DEPTH (args) >= TMPL_ARGS_DEPTH (argvec))
> + /* We're fully specializing a template declaration, so
> + we need to coerce the innermost arguments corresponding to
> + the template. */
> 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 = spec_hasher::hash (gen_tmpl, argvec);
> spec = retrieve_specialization (gen_tmpl, argvec, hash);
> }
> diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic183.C b/gcc/testsuite/g++.dg/cpp0x/variadic183.C
> new file mode 100644
> index 00000000000..27444ebb594
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/variadic183.C
> @@ -0,0 +1,14 @@
> +// PR c++/105956
> +// { dg-do compile { target c++11 } }
> +
> +template<int...> struct list;
> +
> +template<int... Ns> struct impl {
> + static const int idx = 0;
> + using type = list<(idx + Ns)...>;
> +
> + static constexpr const int* a[2] = {(Ns, &idx)...};
> + static_assert(a[0] == &idx && a[1] == &idx, "");
> +};
> +
> +template struct impl<0, 1>;
> --
> 2.37.0.3.g30cc8d0f14
>
>
next prev parent reply other threads:[~2022-07-07 17:15 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-29 17:42 Patrick Palka
2022-07-01 22:44 ` Jason Merrill
2022-07-05 14:06 ` Patrick Palka
2022-07-05 20:29 ` Jason Merrill
2022-07-06 19:26 ` Patrick Palka
2022-07-07 5:00 ` Jason Merrill
2022-07-07 15:16 ` Patrick Palka
2022-07-07 17:15 ` Patrick Palka [this message]
2022-07-07 18:58 ` Jason Merrill
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