On Wed, 31 Jan 2024, Patrick Palka wrote:
> On Wed, 31 Jan 2024, Jason Merrill wrote:
>
> > On 1/31/24 12:12, Patrick Palka wrote:
> > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > > trunk?
> > >
> > > -- >8 --
> > >
> > > Here during declaration matching we undesirably consider the two TT{42}
> > > CTAD expressions to be non-equivalent ultimately because for CTAD
> > > placeholder equivalence we compare the TEMPLATE_DECLs (which uses
> > > pointer identity) and here the corresponding TEMPLATE_DECLs for TT are
> > > different since they're from different scopes. On the other hand, the
> > > corresponding TEMPLATE_TEMPLATE_PARMs are deemed equivalent (since they
> > > have the same position and template parameters). This turns out to be
> > > the root cause of some of the xtreme-header modules regressions.
> > >
> > > We don't have this ttp equivalence issue in other contexts because either
> > > the TEMPLATE_TEMPLATE_PARM is used instead of the TEMPLATE_DECL already
> > > (e.g. when a ttp is used as a targ), or the equivalence logic is relaxed
> > > (e.g. for bound ttps), it seems.
> > >
> > > So this patch relaxes ttp CTAD placeholder equivalence accordingly, by
> > > comparing the TEMPLATE_TEMPLATE_PARM instead of the TEMPLATE_DECL. The
> > > ctp_hasher doesn't need to be adjusted since it currently doesn't include
> > > CLASS_PLACEHOLDER_TEMPLATE in the hash anyway.
> >
> > Maybe put this handling in cp_tree_equal and call it from here? Does
> > iterative_hash_template_arg need something similar?
>
> I was hoping cp_tree_equal would never be called for a ttp TEMPLATE_DECL
> after this patch, and so it wouldn't matter either way, but it turns out
> to matter for a function template-id:
>
> template<template<class> class, class T>
> void g(T);
>
> template<template<class> class TT, class T>
> decltype(g<TT>(T{})) f(T); // #1
>
> template<template<class> class TT, class T>
> decltype(g<TT>(T{})) f(T); // redeclaration of #1
>
> template<class T> struct A { A(T); };
>
> int main() {
> f<A>(0);
> }
>
> Here we represent TT in g<TT> as a TEMPLATE_DECL because it's not until
> coercion that convert_template_argument turns it into a
> TEMPLATE_TEMPLATE_PARM, but of course we can't coerce until the call is
> non-dependent and we know which function we're calling. (So TT within
> a class, variable or alias template-id would be represented as a
> TEMPLATE_TEMPLATE_PARM since we can do coercion ahead of time in that
> case.)
>
> So indeed it seems desirable to handle this in cp_tree_equal... like so?
> Bootstrap and regtest nearly finished.
>
> -- >8 --
>
> PR c++/112737
>
> gcc/cp/ChangeLog:
>
> * pt.cc (iterative_hash_template_arg) <case TEMPLATE_DECL>:
> Adjust hashing to match cp_tree_equal.
> (ctp_hasher::hash): Also hash CLASS_PLACEHOLDER_TEMPLATE.
I forgot to mention this change to ctp_hasher::hash is just a drive-by
optimization, so that CTAD placeholders don't all get the same hash.
> * tree.cc (cp_tree_equal) <case TEMPLATE_DECL>: Return true
> for ttp TEMPLATE_DECLs if their TEMPLATE_TEMPLATE_PARMs are
> equivalent.
> * typeck.cc (structural_comptypes) <case TEMPLATE_TYPE_PARM>:
> Use cp_tree_equal to compare CLASS_PLACEHOLDER_TEMPLATE.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/template/ttp42.C: New test.
> * g++.dg/template/ttp42a.C: New test.
> ---
> gcc/cp/pt.cc | 9 +++++++++
> gcc/cp/tree.cc | 6 +++++-
> gcc/cp/typeck.cc | 4 ++--
> gcc/testsuite/g++.dg/template/ttp42.C | 14 ++++++++++++++
> gcc/testsuite/g++.dg/template/ttp42a.C | 18 ++++++++++++++++++
> 5 files changed, 48 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/template/ttp42.C
> create mode 100644 gcc/testsuite/g++.dg/template/ttp42a.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 5871cb668d0..ca454758ca7 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -1816,6 +1816,13 @@ iterative_hash_template_arg (tree arg, hashval_t val)
> }
> return iterative_hash_template_arg (TREE_TYPE (arg), val);
>
> + case TEMPLATE_DECL:
> + if (DECL_TEMPLATE_TEMPLATE_PARM_P (arg))
> + return iterative_hash_template_arg (TREE_TYPE (arg), val);
> + else
> + /* Hash it like any other declaration. */
> + break;
> +
> case TARGET_EXPR:
> return iterative_hash_template_arg (TARGET_EXPR_INITIAL (arg), val);
>
> @@ -4499,6 +4506,8 @@ struct ctp_hasher : ggc_ptr_hash<tree_node>
> hashval_t val = iterative_hash_object (code, 0);
> val = iterative_hash_object (TEMPLATE_TYPE_LEVEL (t), val);
> val = iterative_hash_object (TEMPLATE_TYPE_IDX (t), val);
> + if (TREE_CODE (t) == TEMPLATE_TYPE_PARM)
> + val = iterative_hash_template_arg (CLASS_PLACEHOLDER_TEMPLATE (t),
> val);
> if (TREE_CODE (t) == BOUND_TEMPLATE_TEMPLATE_PARM)
> val = iterative_hash_template_arg (TYPE_TI_ARGS (t), val);
> --comparing_specializations;
> diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
> index 77f57e0f9ac..5c8c05dc168 100644
> --- a/gcc/cp/tree.cc
> +++ b/gcc/cp/tree.cc
> @@ -4084,11 +4084,15 @@ cp_tree_equal (tree t1, tree t2)
> }
> return false;
>
> + case TEMPLATE_DECL:
> + if (DECL_TEMPLATE_TEMPLATE_PARM_P (t1)
> + && DECL_TEMPLATE_TEMPLATE_PARM_P (t2))
> + return cp_tree_equal (TREE_TYPE (t1), TREE_TYPE (t2));
> + /* Fall through. */
> case VAR_DECL:
> case CONST_DECL:
> case FIELD_DECL:
> case FUNCTION_DECL:
> - case TEMPLATE_DECL:
> case IDENTIFIER_NODE:
> case SSA_NAME:
> case USING_DECL:
> diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
> index a15eda3f5f8..87109e63138 100644
> --- a/gcc/cp/typeck.cc
> +++ b/gcc/cp/typeck.cc
> @@ -1573,8 +1573,8 @@ structural_comptypes (tree t1, tree t2, int strict)
> return false;
> /* If T1 and T2 don't represent the same class template deduction,
> they aren't equal. */
> - if (CLASS_PLACEHOLDER_TEMPLATE (t1)
> - != CLASS_PLACEHOLDER_TEMPLATE (t2))
> + if (!cp_tree_equal (CLASS_PLACEHOLDER_TEMPLATE (t1),
> + CLASS_PLACEHOLDER_TEMPLATE (t2)))
> return false;
> /* Constrained 'auto's are distinct from parms that don't have the same
> constraints. */
> diff --git a/gcc/testsuite/g++.dg/template/ttp42.C
> b/gcc/testsuite/g++.dg/template/ttp42.C
> new file mode 100644
> index 00000000000..da08e857fc5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/ttp42.C
> @@ -0,0 +1,14 @@
> +// PR c++/112737
> +// { dg-do compile { target c++17 } }
> +
> +template<template<class> class TT>
> +decltype(TT{42}) f(); // #1
> +
> +template<template<class> class TT>
> +decltype(TT{42}) f(); // redeclaration of #1
> +
> +template<class T> struct A { A(T); };
> +
> +int main() {
> + f<A>();
> +}
> diff --git a/gcc/testsuite/g++.dg/template/ttp42a.C
> b/gcc/testsuite/g++.dg/template/ttp42a.C
> new file mode 100644
> index 00000000000..e890deda3a3
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/ttp42a.C
> @@ -0,0 +1,18 @@
> +// PR c++/112737
> +// A version of ttp42.C using a function template-id instead of ttp CTAD.
> +// { dg-do compile { target c++11 } }
> +
> +template<template<class> class, class T>
> +void g(T);
> +
> +template<template<class> class TT, class T>
> +decltype(g<TT>(T{})) f(T); // #1
> +
> +template<template<class> class TT, class T>
> +decltype(g<TT>(T{})) f(T); // redeclaration of #1
> +
> +template<class T> struct A { A(T); };
> +
> +int main() {
> + f<A>(0);
> +}
> --
> 2.43.0.493.gbc7ee2e5e1
>
>
