On Thu, 1 Jun 2023, Patrick Palka wrote: > For a complex alias template-id, dependent_alias_template_spec_p returns > true if any template argument of the template-id is dependent. This > predicate indicates that substitution into the template-id may behave > differently with respect to SFINAE than substitution into the expanded > alias, and so the alias is in a way non-transparent. For example > 'first_t<T, T&>' in > > template<class T, class...> using first_t = T; > template<class T> first_t<T, T&> f(); > > is such an alias template-id since first_t doesn't use its second > template parameter and so the substitution into the expanded alias would > discard the SFINAE effects of the corresponding (dependent) argument 'T&'. > > But this predicate is overly conservative since what really matters for > sake of SFINAE equivalence is whether a template argument corresponding > to an _unused_ template parameter is dependent. So the predicate should > return false for e.g. 'first_t<T, int>' or 'first_t<T>'. > > This patch refines the predicate appropriately. We need to be able to > efficiently determine which template parameters of a complex alias > template are unused, so to that end we add a new out parameter to > complex_alias_template_p and cache its result in an on-the-side > hash_map that replaces the existing TEMPLATE_DECL_COMPLEX_ALIAS_P > flag. And in doing so, we fix a latent bug that this flag wasn't > being propagated during partial instantiation, and so we were treating > all partially instantiated member alias templates as non-complex.
Whoops, this last sentence is wrong I think. The flag propagation would have happened via the call to copy_decl from tsubst_template_decl, so there was no latent bug. > > PR c++/90679 > > gcc/cp/ChangeLog: > > * cp-tree.h (TEMPLATE_DECL_COMPLEX_ALIAS_P): Remove. > (most_general_template): Constify parameter. > * pt.cc (push_template_decl): Adjust after removing > TEMPLATE_DECL_COMPLEX_ALIAS_P. > (complex_alias_tmpl_info): New hash_map. > (uses_all_template_parms_data::seen): Change type to > tree* from bool*. > (complex_alias_template_r): Adjust accordingly. > (complex_alias_template_p): Add 'seen_out' out parameter. > Call most_general_template and check PRIMARY_TEMPLATE_P. > Use complex_alias_tmpl_info to cache the result and set > '*seen_out' accordigly. > (dependent_alias_template_spec_p): Add !processing_template_decl > early exit test. Consider dependence of only template arguments > corresponding to seen template parameters as per > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/alias-decl-75.C: New test. > --- > gcc/cp/cp-tree.h | 7 +- > gcc/cp/pt.cc | 101 +++++++++++++++------ > gcc/testsuite/g++.dg/cpp0x/alias-decl-75.C | 24 +++++ > 3 files changed, 100 insertions(+), 32 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-75.C > > diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h > index a1b882f11fe..5330d1e1f62 100644 > --- a/gcc/cp/cp-tree.h > +++ b/gcc/cp/cp-tree.h > @@ -543,7 +543,6 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX]; > 2: DECL_THIS_EXTERN (in VAR_DECL, FUNCTION_DECL or PARM_DECL) > DECL_IMPLICIT_TYPEDEF_P (in a TYPE_DECL) > DECL_CONSTRAINT_VAR_P (in a PARM_DECL) > - TEMPLATE_DECL_COMPLEX_ALIAS_P (in TEMPLATE_DECL) > DECL_INSTANTIATING_NSDMI_P (in a FIELD_DECL) > USING_DECL_UNRELATED_P (in USING_DECL) > 3: DECL_IN_AGGR_P. > @@ -3655,10 +3654,6 @@ struct GTY(()) lang_decl { > #define TYPE_DECL_ALIAS_P(NODE) \ > DECL_LANG_FLAG_6 (TYPE_DECL_CHECK (NODE)) > > -/* Nonzero for TEMPLATE_DECL means that it is a 'complex' alias template. */ > -#define TEMPLATE_DECL_COMPLEX_ALIAS_P(NODE) \ > - DECL_LANG_FLAG_2 (TEMPLATE_DECL_CHECK (NODE)) > - > /* Nonzero for a type which is an alias for another type; i.e, a type > which declaration was written 'using name-of-type = > another-type'. */ > @@ -7403,7 +7398,7 @@ extern tree tsubst_argument_pack (tree, > tree, tsubst_flags_t, tree); > extern tree tsubst_template_args (tree, tree, tsubst_flags_t, > tree); > extern tree tsubst_template_arg (tree, tree, > tsubst_flags_t, tree); > extern tree tsubst_function_parms (tree, tree, tsubst_flags_t, > tree); > -extern tree most_general_template (tree); > +extern tree most_general_template (const_tree); > extern tree get_mostly_instantiated_function_type (tree); > extern bool problematic_instantiation_changed (void); > extern void record_last_problematic_instantiation (void); > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > index 7fb3e75bceb..1b28195e10d 100644 > --- a/gcc/cp/pt.cc > +++ b/gcc/cp/pt.cc > @@ -211,7 +211,6 @@ static tree listify (tree); > static tree listify_autos (tree, tree); > static tree tsubst_template_parm (tree, tree, tsubst_flags_t); > static tree instantiate_alias_template (tree, tree, tsubst_flags_t); > -static bool complex_alias_template_p (const_tree tmpl); > static tree get_underlying_template (tree); > static tree tsubst_attributes (tree, tree, tsubst_flags_t, tree); > static tree canonicalize_expr_argument (tree, tsubst_flags_t); > @@ -6233,8 +6232,6 @@ push_template_decl (tree decl, bool is_friend) > constr = build_constraints (constr, NULL_TREE); > set_constraints (decl, constr); > } > - if (complex_alias_template_p (tmpl)) > - TEMPLATE_DECL_COMPLEX_ALIAS_P (tmpl) = true; > } > } > > @@ -6526,12 +6523,16 @@ alias_template_specialization_p (const_tree t, > return NULL_TREE; > } > > +/* A cache of the result of complex_alias_template_p. */ > + > +static GTY(()) hash_map<const_tree, tree> *complex_alias_tmpl_info; > + > /* Data structure for complex_alias_template_*. */ > > struct uses_all_template_parms_data > { > int level; > - bool *seen; > + tree *seen; > }; > > /* walk_tree callback for complex_alias_template_p. */ > @@ -6551,7 +6552,7 @@ complex_alias_template_r (tree *tp, int *walk_subtrees, > void *data_) > { > tree idx = get_template_parm_index (t); > if (TEMPLATE_PARM_LEVEL (idx) == data.level) > - data.seen[TEMPLATE_PARM_IDX (idx)] = true; > + data.seen[TEMPLATE_PARM_IDX (idx)] = boolean_true_node; > } > > default:; > @@ -6576,7 +6577,7 @@ complex_alias_template_r (tree *tp, int *walk_subtrees, > void *data_) > return t; > > /* Consider the expanded packs to be used outside the expansion... */ > - data.seen[idx] = true; > + data.seen[idx] = boolean_true_node; > } > > /* ...but don't walk into the pattern. Consider PR104008: > @@ -6598,12 +6599,17 @@ complex_alias_template_r (tree *tp, int > *walk_subtrees, void *data_) > using that alias can be ill-formed when the expansion is not, as with > the void_t template. > > - Returns 1 if always complex, 0 if not complex, -1 if complex iff any of > the > - template arguments are empty packs. */ > + If this predicate returns true in the ordinary case, the out parameter > + SEEN_OUT is set to a TREE_VEC containing boolean_true_node at element I if > + the I'th template parameter of the alias template is used in the alias. > */ > > static bool > -complex_alias_template_p (const_tree tmpl) > +complex_alias_template_p (const_tree tmpl, tree *seen_out) > { > + tmpl = most_general_template (tmpl); > + if (!PRIMARY_TEMPLATE_P (tmpl)) > + return false; > + > /* A renaming alias isn't complex. */ > if (get_underlying_template (CONST_CAST_TREE (tmpl)) != tmpl) > return false; > @@ -6612,26 +6618,52 @@ complex_alias_template_p (const_tree tmpl) > if (get_constraints (tmpl)) > return true; > > + if (tree *slot = hash_map_safe_get (complex_alias_tmpl_info, tmpl)) > + { > + tree result = *slot; > + if (result == boolean_false_node) > + return false; > + if (result == boolean_true_node) > + return true; > + gcc_assert (TREE_CODE (result) == TREE_VEC); > + if (seen_out) > + *seen_out = result; > + return true; > + } > + > struct uses_all_template_parms_data data; > tree pat = DECL_ORIGINAL_TYPE (DECL_TEMPLATE_RESULT (tmpl)); > tree parms = DECL_TEMPLATE_PARMS (tmpl); > data.level = TMPL_PARMS_DEPTH (parms); > int len = TREE_VEC_LENGTH (INNERMOST_TEMPLATE_PARMS (parms)); > - data.seen = XALLOCAVEC (bool, len); > + tree seen = make_tree_vec (len); > + data.seen = TREE_VEC_BEGIN (seen); > for (int i = 0; i < len; ++i) > - data.seen[i] = false; > + data.seen[i] = boolean_false_node; > > if (cp_walk_tree_without_duplicates (&pat, complex_alias_template_r, > &data)) > - return true; > - for (int i = 0; i < len; ++i) > - if (!data.seen[i]) > + { > + hash_map_safe_put<hm_ggc> (complex_alias_tmpl_info, tmpl, > boolean_true_node); > return true; > + } > + > + for (int i = 0; i < len; ++i) > + if (data.seen[i] != boolean_true_node) > + { > + hash_map_safe_put<hm_ggc> (complex_alias_tmpl_info, tmpl, seen); > + if (seen_out) > + *seen_out = seen; > + return true; > + } > + > + hash_map_safe_put<hm_ggc> (complex_alias_tmpl_info, tmpl, > boolean_false_node); > return false; > } > > -/* If T is a specialization of a complex alias template with dependent > - template-arguments, return it; otherwise return NULL_TREE. If T is a > - typedef to such a specialization, return the specialization. */ > +/* If T is a specialization of a complex alias template with a dependent > + argument for an unused template parameter, return it; otherwise return > + NULL_TREE. If T is a typedef to such a specialization, return the > + specialization. */ > > tree > dependent_alias_template_spec_p (const_tree t, bool transparent_typedefs) > @@ -6640,15 +6672,32 @@ dependent_alias_template_spec_p (const_tree t, bool > transparent_typedefs) > return NULL_TREE; > gcc_assert (TYPE_P (t)); > > - if (!typedef_variant_p (t)) > + if (!processing_template_decl || !typedef_variant_p (t)) > return NULL_TREE; > > - tree tinfo = TYPE_ALIAS_TEMPLATE_INFO (t); > - if (tinfo > - && TEMPLATE_DECL_COMPLEX_ALIAS_P (TI_TEMPLATE (tinfo)) > - && (any_dependent_template_arguments_p > - (INNERMOST_TEMPLATE_ARGS (TI_ARGS (tinfo))))) > - return CONST_CAST_TREE (t); > + if (tree tinfo = TYPE_ALIAS_TEMPLATE_INFO (t)) > + { > + tree seen = NULL_TREE; > + if (complex_alias_template_p (TI_TEMPLATE (tinfo), &seen)) > + { > + tree args = INNERMOST_TEMPLATE_ARGS (TI_ARGS (tinfo)); > + if (!seen) > + { > + if (any_dependent_template_arguments_p (args)) > + return CONST_CAST_TREE (t); > + } > + else > + { > + gcc_assert (TREE_VEC_LENGTH (args) == TREE_VEC_LENGTH (seen)); > + for (int i = 0, len = TREE_VEC_LENGTH (args); i < len; ++i) > + if (TREE_VEC_ELT (seen, i) != boolean_true_node > + && dependent_template_arg_p (TREE_VEC_ELT (args, i))) > + return CONST_CAST_TREE (t); > + } > + > + return NULL_TREE; > + } > + } > > if (transparent_typedefs) > { > @@ -25958,7 +26007,7 @@ most_specialized_instantiation (tree templates) > `template <class T> template <class U> S<T*>::f(U)'. */ > > tree > -most_general_template (tree decl) > +most_general_template (const_tree decl) > { > if (TREE_CODE (decl) != TEMPLATE_DECL) > { > @@ -25992,7 +26041,7 @@ most_general_template (tree decl) > decl = DECL_TI_TEMPLATE (decl); > } > > - return decl; > + return CONST_CAST_TREE (decl); > } > > /* Return the most specialized of the template partial specializations > diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-75.C > b/gcc/testsuite/g++.dg/cpp0x/alias-decl-75.C > new file mode 100644 > index 00000000000..10592f521a0 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-75.C > @@ -0,0 +1,24 @@ > +// PR c++/90679 > +// { dg-do compile { target c++11 } } > + > +template<class T, class...> > +using first_t = T; > + > +template<class T> > +struct A; > + > +template<class T> > +struct traits; > + > +template<class T> > +struct traits<A<first_t<T>>> { > + static constexpr int value = 1; > +}; > + > +template<class T> > +struct traits<A<first_t<const T>>> { > + static constexpr int value = 2; > +}; > + > +static_assert(traits<A<int>>::value == 1, ""); > +static_assert(traits<A<const int>>::value == 2, ""); // { dg-bogus > "ambiguous" } > -- > 2.41.0.rc1.10.g9e49351c30 > >