From df4f95dbd4764ffc1e8270e5b3c0fd71b6724562 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Fri, 3 Jun 2022 09:08:41 -0400 Subject: [PATCH] c++: find_template_parameters and PARM_DECLs [PR105797] As explained in r11-4959-gde6f64f9556ae3, the atom cache assumes two equivalent expressions (according to cp_tree_equal) must use the same template parameters (according to find_template_parameters). This assumption turned out to not hold for TARGET_EXPR, which was addressed by that commit. But this assumption apparently doesn't hold for PARM_DECL either: find_template_parameters walks its DECL_CONTEXT but cp_tree_equal by default doesn't consider DECL_CONTEXT unless comparing_specializations is set. Thus in the first testcase below, the atomic constraints of #1 and #2 are equivalent according to cp_tree_equal, but according to find_template_parameters the former uses T and the latter uses both T and U (surprisingly). We could fix this assumption violation by setting comparing_specializations in the atom_hasher, which would make cp_tree_equal return false for the two atoms, but that seems overly pessimistic here. Ideally the atoms should continue being considered equivalent and we instead fix find_template_paremeters to return just T for #2's atom. To that end this patch makes for_each_template_parm_r stop walking the DECL_CONTEXT of a PARM_DECL. This should be safe to do because tsubst_copy / tsubst_decl only substitutes the TREE_TYPE of a PARM_DECL and doesn't bother substituting the DECL_CONTEXT, thus the only relevant template parameters are those used in its type. any_template_parm_r is currently responsible for walking its TREE_TYPE, but I suppose it now makes sense for for_each_template_parm_r to do so instead. In passing this patch also makes for_each_template_parm_r stop walking the DECL_CONTEXT of a VAR_/FUNCTION_DECL since doing so after walking DECL_TI_ARGS is redundant, I think. I experimented with not walking DECL_CONTEXT for CONST_DECL, but the second testcase below demonstrates it's necessary to walk it. PR c++/105797 gcc/cp/ChangeLog: * pt.cc (for_each_template_parm_r) : Don't walk DECL_CONTEXT. : Likewise. Walk TREE_TYPE. : Simplify. (any_template_parm_r) : Don't walk TREE_TYPE. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-decltype4.C: New test. * g++.dg/cpp2a/concepts-memfun3.C: New test. --- gcc/cp/pt.cc | 10 +++++----- gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C | 16 ++++++++++++++++ gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C | 12 ++++++++++++ 3 files changed, 33 insertions(+), 5 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index 836861e10391..d0c4c9889c9e 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -10561,11 +10561,14 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d) case VAR_DECL: if (DECL_LANG_SPECIFIC (t) && DECL_TEMPLATE_INFO (t)) WALK_SUBTREE (DECL_TI_ARGS (t)); - /* Fall through. */ + break; case PARM_DECL: + WALK_SUBTREE (TREE_TYPE (t)); + break; + case CONST_DECL: - if (TREE_CODE (t) == CONST_DECL && DECL_TEMPLATE_PARM_P (t)) + if (DECL_TEMPLATE_PARM_P (t)) WALK_SUBTREE (DECL_INITIAL (t)); if (DECL_CONTEXT (t) && pfd->include_nondeduced_p) @@ -10824,9 +10827,6 @@ any_template_parm_r (tree t, void *data) break; case TEMPLATE_PARM_INDEX: - case PARM_DECL: - /* A parameter or constraint variable may also depend on a template - parameter without explicitly naming it. */ WALK_SUBTREE (TREE_TYPE (t)); break; diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C b/gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C new file mode 100644 index 000000000000..6683d224cf8f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C @@ -0,0 +1,16 @@ +// PR c++/105797 +// { dg-do compile { target c++20 } } + +template +concept C = requires { T(); }; + +template +void f(T v) requires C; // #1 + +template +void f(T v) requires C; // #2 + +int main() { + f(0); + f(0); +} diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C new file mode 100644 index 000000000000..beb30d0e3506 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C @@ -0,0 +1,12 @@ +// { dg-do compile { target c++20 } } + +template +struct A { + enum E { e = I }; + static void f() requires (e != 0); +}; + +int main() { + A<1>::f(); + A<0>::f(); // { dg-error "no match" } +}