On Wed, 2 Feb 2022, Jason Merrill wrote:
> On 2/2/22 13:21, Patrick Palka wrote:
> > On Wed, 2 Feb 2022, Patrick Palka wrote:
> >
> > > Here we're crashing during satisfaction of the lambda's placeholder type
> > > constraints because the constraints depend on the template arguments
> > > from the enclosing scope, which aren't a part of the lambda's
> > > DECL_TI_ARGS. So when inside a lambda, do_auto_deduction needs to add
> > > the "regenerating" template arguments to the set of outer template
> > > arguments, like we already do in satisfy_declaration_constraints.
> > >
> > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > > trunk and perhaps 11?
> > >
> > > PR c++/103706
> > >
> > > gcc/cp/ChangeLog:
> > >
> > > * constraint.cc (satisfy_declaration_constraints): Use
> > > lambda_regenerating_args instead.
> > > * cp-tree.h (lambda_regenerating_args): Declare.
> > > * pt.cc (add_to_template_args): Handle NULL_TREE extra_args
> > > gracefully.
> > > (lambda_regenerating_args): Define, split out from
> > > satisfy_declaration_constraints.
> > > (do_auto_deduction): Use lambda_regenerating_args to obtain the
> > > full set of outer template arguments when checking the
> > > constraint on a placeholder type within a lambda.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > * g++.dg/cpp2a/concepts-lambda18.C: New test.
> > > ---
> > > gcc/cp/constraint.cc | 9 +----
> > > gcc/cp/cp-tree.h | 1 +
> > > gcc/cp/pt.cc | 37 ++++++++++++++++---
> > > .../g++.dg/cpp2a/concepts-lambda18.C | 14 +++++++
> > > 4 files changed, 48 insertions(+), 13 deletions(-)
> > > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
> > >
> > > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> > > index cc4df4216ef..c41ee02b910 100644
> > > --- a/gcc/cp/constraint.cc
> > > +++ b/gcc/cp/constraint.cc
> > > @@ -3148,18 +3148,13 @@ satisfy_declaration_constraints (tree t, sat_info
> > > info)
> > > args = add_outermost_template_args (args, inh_ctor_targs);
> > > }
> > > - if (regenerated_lambda_fn_p (t))
> > > + if (LAMBDA_FUNCTION_P (t))
> > > {
> > > /* The TI_ARGS of a regenerated lambda contains only the innermost
> > > set of template arguments. Augment this with the outer
> > > template
> > > arguments that were used to regenerate the lambda. */
> > > gcc_assert (!args || TMPL_ARGS_DEPTH (args) == 1);
> > > - tree lambda = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (t));
> > > - tree outer_args = TI_ARGS (LAMBDA_EXPR_REGEN_INFO (lambda));
> > > - if (args)
> > > - args = add_to_template_args (outer_args, args);
> > > - else
> > > - args = outer_args;
> > > + args = add_to_template_args (lambda_regenerating_args (t), args);
> > > }
> > > /* If any arguments depend on template parameters, we can't
> > > diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> > > index b9eb71fbc3a..7a7fe5ba599 100644
> > > --- a/gcc/cp/cp-tree.h
> > > +++ b/gcc/cp/cp-tree.h
> > > @@ -7715,6 +7715,7 @@ extern void finish_lambda_scope
> > > (void);
> > > extern tree start_lambda_function (tree fn, tree
> > > lambda_expr);
> > > extern void finish_lambda_function (tree body);
> > > extern bool regenerated_lambda_fn_p (tree);
> > > +extern tree lambda_regenerating_args (tree);
> > > extern tree most_general_lambda (tree);
> > > extern tree finish_omp_target (location_t, tree,
> > > tree, bool);
> > > extern void finish_omp_target_clauses (location_t, tree,
> > > tree *);
> > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > > index 6e129da1d05..c919d2de68f 100644
> > > --- a/gcc/cp/pt.cc
> > > +++ b/gcc/cp/pt.cc
> > > @@ -573,6 +573,9 @@ add_to_template_args (tree args, tree extra_args)
> > > if (args == NULL_TREE || extra_args == error_mark_node)
> > > return extra_args;
> > > + if (extra_args == NULL_TREE)
> > > + return args;
> > > +
> >
> > Whoops, this last-minute change to add_to_template_args turned out to
> > be a bad idea as some callers apparently rely on add_to_template_args
> > treating NULL_TREE extra_args as a depth 1 targ vector (whereas for
> > the calls in satisfy_declaration_constraints and do_auto_deduction we
> > want NULL_TREE extra_args to be treated as a depth 0 targ vector).
> >
> > Please consider the below patch instead, which doesn't attempt to change
> > the behavior of add_to_template_args:
> >
> > -- >8 --
> >
> > Subject: [PATCH] c++: constrained auto in lambda using outer tparms
> > [PR103706]
> >
> > Here we're crashing during satisfaction of the lambda's placeholder type
> > constraints because the constraints depend on the template arguments
> > from the enclosing scope, which aren't part of the lambda's DECL_TI_ARGS.
> > So when inside a lambda, do_auto_deduction needs to add its
> > "regenerating" template arguments to the set of outer template
> > arguments, like we already do in satisfy_declaration_constraints.
> >
> > PR c++/103706
> >
> > gcc/cp/ChangeLog:
> >
> > * constraint.cc (satisfy_declaration_constraints): Use
> > lambda_regenerating_args instead.
> > * cp-tree.h (lambda_regenerating_args): Declare.
> > * pt.cc (lambda_regenerating_args): Define, split out from
> > satisfy_declaration_constraints.
> > (do_auto_deduction): Use lambda_regenerating_args to obtain the
> > full set of outer template arguments for satisfaction.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp2a/concepts-lambda18.C: New test.
> > ---
> > gcc/cp/constraint.cc | 9 ++---
> > gcc/cp/cp-tree.h | 1 +
> > gcc/cp/pt.cc | 39 ++++++++++++++++---
> > .../g++.dg/cpp2a/concepts-lambda18.C | 14 +++++++
> > 4 files changed, 52 insertions(+), 11 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
> >
> > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> > index cc4df4216ef..c0ebe63a0a2 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -3148,18 +3148,17 @@ satisfy_declaration_constraints (tree t, sat_info
> > info)
> > args = add_outermost_template_args (args, inh_ctor_targs);
> > }
> > - if (regenerated_lambda_fn_p (t))
> > + if (LAMBDA_FUNCTION_P (t))
>
> I wonder why you changed this test? OK either way.
No good reason, it shouldn't make a functional difference so I'll drop
this no-op change.
>
> > {
> > /* The TI_ARGS of a regenerated lambda contains only the innermost
> > set of template arguments. Augment this with the outer template
> > arguments that were used to regenerate the lambda. */
> > gcc_assert (!args || TMPL_ARGS_DEPTH (args) == 1);
> > - tree lambda = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (t));
> > - tree outer_args = TI_ARGS (LAMBDA_EXPR_REGEN_INFO (lambda));
> > + tree regen_args = lambda_regenerating_args (t);
> > if (args)
> > - args = add_to_template_args (outer_args, args);
> > + args = add_to_template_args (regen_args, args);
> > else
> > - args = outer_args;
> > + args = regen_args;
> > }
> > /* If any arguments depend on template parameters, we can't
> > diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> > index b9eb71fbc3a..7a7fe5ba599 100644
> > --- a/gcc/cp/cp-tree.h
> > +++ b/gcc/cp/cp-tree.h
> > @@ -7715,6 +7715,7 @@ extern void finish_lambda_scope
> > (void);
> > extern tree start_lambda_function (tree fn, tree lambda_expr);
> > extern void finish_lambda_function (tree body);
> > extern bool regenerated_lambda_fn_p (tree);
> > +extern tree lambda_regenerating_args (tree);
> > extern tree most_general_lambda (tree);
> > extern tree finish_omp_target (location_t, tree,
> > tree, bool);
> > extern void finish_omp_target_clauses (location_t, tree,
> > tree *);
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index 6e129da1d05..46754c611e7 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -14442,6 +14442,21 @@ most_general_lambda (tree t)
> > return t;
> > }
> > +/* Return the set of template arguments used to regenerate the lambda T
> > + from its most general lambda. */
> > +
> > +tree
> > +lambda_regenerating_args (tree t)
> > +{
> > + if (LAMBDA_FUNCTION_P (t))
> > + t = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (t));
> > + gcc_assert (TREE_CODE (t) == LAMBDA_EXPR);
> > + if (tree ti = LAMBDA_EXPR_REGEN_INFO (t))
> > + return TI_ARGS (ti);
> > + else
> > + return NULL_TREE;
> > +}
> > +
> > /* We're instantiating a variable from template function TCTX. Return the
> > corresponding current enclosing scope. We can match them up using
> > DECL_SOURCE_LOCATION because lambdas only ever have one source
> > location, and
> > @@ -30100,12 +30115,24 @@ do_auto_deduction (tree type, tree init, tree
> > auto_node,
> > return type;
> > }
> > - if ((context == adc_return_type
> > - || context == adc_variable_type
> > - || context == adc_decomp_type)
> > - && current_function_decl
> > - && DECL_TEMPLATE_INFO (current_function_decl))
> > - outer_targs = DECL_TI_ARGS (current_function_decl);
> > + if (context == adc_return_type
> > + || context == adc_variable_type
> > + || context == adc_decomp_type)
> > + if (tree fn = current_function_decl)
> > + if (DECL_TEMPLATE_INFO (fn) || LAMBDA_FUNCTION_P (fn))
> > + {
> > + outer_targs
> > + = DECL_TEMPLATE_INFO (fn) ? DECL_TI_ARGS (fn) : NULL_TREE;
> > + if (LAMBDA_FUNCTION_P (fn))
> > + {
> > + /* As in satisfy_declaration_constraints. */
> > + tree regen_args = lambda_regenerating_args (fn);
> > + if (outer_targs)
> > + outer_targs = add_to_template_args (regen_args,
> > outer_targs);
> > + else
> > + outer_targs = regen_args;
> > + }
> > + }
> > tree full_targs = add_to_template_args (outer_targs, targs);
> > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
> > b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
> > new file mode 100644
> > index 00000000000..f1058daf317
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda18.C
> > @@ -0,0 +1,14 @@
> > +// PR c++/103706
> > +// { dg-do compile { target c++20 } }
> > +
> > +template<class T, class U> concept C = __is_same(U, int);
> > +
> > +template<class T> void f() {
> > + []() -> C<T> auto {
> > + C<T> auto x = T(); // { dg-error "constraints" }
> > + return T(); // { dg-error "constraints" }
> > + }();
> > +}
> > +
> > +template void f<int>(); // { dg-bogus "" }
> > +template void f<char>(); // { dg-message "required from here" }
>
>
Re: [PATCH] c++: constrained auto in lambda using outer tparms [PR103706]
Patrick Palka via Gcc-patches Thu, 03 Feb 2022 09:17:29 -0800
- [PATCH] c++: constrained auto in lambda usin... Patrick Palka via Gcc-patches
- Re: [PATCH] c++: constrained auto in la... Patrick Palka via Gcc-patches
- Re: [PATCH] c++: constrained auto i... Jason Merrill via Gcc-patches
- Re: [PATCH] c++: constrained au... Patrick Palka via Gcc-patches
