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From: Patrick Palka <ppalka@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r11-9992] c++: deduction guides and ttp rewriting [PR102479] Date: Fri, 13 May 2022 13:40:10 +0000 (GMT) [thread overview] Message-ID: <20220513134010.29E8C395C41A@sourceware.org> (raw) https://gcc.gnu.org/g:f705d0f2d03cc4d9f890832798b3352553f2262f commit r11-9992-gf705d0f2d03cc4d9f890832798b3352553f2262f Author: Patrick Palka <ppalka@redhat.com> Date: Mon Sep 27 16:01:10 2021 -0400 c++: deduction guides and ttp rewriting [PR102479] The problem here is ultimately that rewrite_tparm_list when rewriting a TEMPLATE_TEMPLATE_PARM introduces a tree cycle in the rewritten ttp that structural_comptypes can't cope with. In particular the DECL_TEMPLATE_PARMS of a ttp's TEMPLATE_DECL normally captures an empty parameter list at its own level (and so the TEMPLATE_DECL doesn't appear in its own DECL_TEMPLATE_PARMS), but rewrite_tparm_list ends up giving it a complete parameter list. In the new testcase below, this causes infinite recursion from structural_comptypes when comparing Tmpl<char> with Tmpl<long> (where both 'Tmpl's are rewritten ttps). This patch fixes this by making rewrite_template_parm give a rewritten template template parm an empty parameter list at its own level, thereby avoiding the tree cycle. Testing the alias CTAD case revealed that we're not setting current_template_parms in alias_ctad_tweaks, which this patch also fixes. PR c++/102479 gcc/cp/ChangeLog: * pt.c (rewrite_template_parm): Handle single-level tsubst_args. Avoid a tree cycle when assigning the DECL_TEMPLATE_PARMS for a rewritten ttp. (alias_ctad_tweaks): Set current_template_parms accordingly. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/class-deduction12.C: Also test alias CTAD in the same way. * g++.dg/cpp1z/class-deduction99.C: New test. (cherry picked from commit 51018dd1395c72b3681ae5f84eceb94320472922) Diff: --- gcc/cp/pt.c | 20 ++++++++++++--- gcc/testsuite/g++.dg/cpp1z/class-deduction12.C | 6 +++++ gcc/testsuite/g++.dg/cpp1z/class-deduction99.C | 35 ++++++++++++++++++++++++++ 3 files changed, 58 insertions(+), 3 deletions(-) diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index a8fa2347c8a..ba505820c6a 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -28733,7 +28733,7 @@ rewrite_template_parm (tree olddecl, unsigned index, unsigned level, const int depth = TMPL_ARGS_DEPTH (tsubst_args); tree ttargs = make_tree_vec (depth + 1); for (int i = 0; i < depth; ++i) - TREE_VEC_ELT (ttargs, i) = TREE_VEC_ELT (tsubst_args, i); + TREE_VEC_ELT (ttargs, i) = TMPL_ARGS_LEVEL (tsubst_args, i + 1); TREE_VEC_ELT (ttargs, depth) = template_parms_level_to_args (ttparms); // Substitute ttargs into ttparms to fix references to @@ -28746,8 +28746,17 @@ rewrite_template_parm (tree olddecl, unsigned index, unsigned level, ttparms = tsubst_template_parms_level (ttparms, ttargs, complain); // Finally, tack the adjusted parms onto tparms. - ttparms = tree_cons (size_int (depth), ttparms, - current_template_parms); + ttparms = tree_cons (size_int (level + 1), ttparms, + copy_node (current_template_parms)); + // As with all template template parms, the parameter list captured + // by this template template parm that corresponds to its own level + // should be empty. This avoids infinite recursion when structurally + // comparing two such rewritten template template parms (PR102479). + gcc_assert (!TREE_VEC_LENGTH + (TREE_VALUE (TREE_CHAIN (DECL_TEMPLATE_PARMS (olddecl))))); + gcc_assert (TMPL_PARMS_DEPTH (TREE_CHAIN (ttparms)) == level); + TREE_VALUE (TREE_CHAIN (ttparms)) = make_tree_vec (0); + // All done. DECL_TEMPLATE_PARMS (newdecl) = ttparms; } } @@ -29245,6 +29254,11 @@ alias_ctad_tweaks (tree tmpl, tree uguides) ++ndlen; tree gtparms = make_tree_vec (natparms + ndlen); + /* Set current_template_parms as in build_deduction_guide. */ + auto ctp = make_temp_override (current_template_parms); + current_template_parms = copy_node (DECL_TEMPLATE_PARMS (tmpl)); + TREE_VALUE (current_template_parms) = gtparms; + /* First copy over the parms of A. */ for (j = 0; j < natparms; ++j) TREE_VEC_ELT (gtparms, j) = TREE_VEC_ELT (atparms, j); diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction12.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction12.C index a31cc1526db..f0d7ea0e16b 100644 --- a/gcc/testsuite/g++.dg/cpp1z/class-deduction12.C +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction12.C @@ -15,3 +15,9 @@ A a(&i,2,B<42>()); template <class,class> class same; template <class T> class same<T,T> {}; same<decltype(a), A<int*>> s; + +#if __cpp_deduction_guides >= 201907 +template <class T> using C = A<const T*>; + +same<decltype(C(&i, 2, B<42>())), A<const int*>> t; +#endif diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction99.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction99.C new file mode 100644 index 00000000000..6daa4b7c55c --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction99.C @@ -0,0 +1,35 @@ +// PR c++/102479 +// { dg-do compile { target c++17 } } + +template<class T> struct A; + +template<class T> +struct tuple { + tuple(T); + + template<template<class> class Tmpl> + tuple(Tmpl<T>); + + template<template<class> class Tmpl, typename A<Tmpl<char>>::type = 0> + tuple(Tmpl<T>); + + template<template<class> class Tmpl, typename A<Tmpl<long>>::type = 0> + tuple(Tmpl<T>); +}; + +template<class T> struct B { }; + +using ty1 = tuple<int>; +using ty1 = decltype(tuple(0)); +using ty1 = decltype(tuple(B<int>{})); + +#if __cpp_deduction_guides >= 201907 +template<class T> using const_tuple = tuple<const T>; + +using ty2 = const_tuple<int>; +using ty2 = decltype(const_tuple(0)); +using ty2 = decltype(const_tuple(B<const int>{})); + +using ty3 = const_tuple<B<int>>; +using ty3 = decltype(const_tuple(B<int>{})); +#endif
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