From 8d5d90878ea9731301d3a1af32a444e4772e65e4 Mon Sep 17 00:00:00 2001 From: Jason Merrill Date: Tue, 19 Nov 2019 15:22:12 -0500 Subject: [PATCH] Consider parm types equivalence for operator rewrite tiebreaker. The C++ committee continues to discuss how best to avoid breaking existing code with the new rules for reversed operators. A recent suggestion was to base the tie-breaker on the parameter types of the candidates, which made a lot of sense to me, so this patch implements that. This patch also mentions that a candidate was reversed or rewritten when printing the list of candidates, and warns about a comparison that becomes recursive under the new rules. There is no flag for this warning; people can silence it by swapping the operands. * call.c (same_fn_or_template): Change to cand_parms_match. (joust): Adjust. (print_z_candidate): Mark rewritten/reversed candidates. (build_new_op_1): Warn about recursive call with reversed arguments. From-SVN: r278465 --- gcc/cp/ChangeLog | 7 +++ gcc/cp/call.c | 63 ++++++++++++------- .../g++.dg/cpp2a/spaceship-rewrite2.C | 12 ++++ .../g++.dg/cpp2a/spaceship-rewrite3.C | 10 +++ .../g++.dg/cpp2a/spaceship-rewrite4.C | 12 ++++ 5 files changed, 80 insertions(+), 24 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite2.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite3.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite4.C diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog index cc7a58ec5fd..2313a824b48 100644 --- a/gcc/cp/ChangeLog +++ b/gcc/cp/ChangeLog @@ -1,3 +1,10 @@ +2019-11-12 Jason Merrill + + * call.c (same_fn_or_template): Change to cand_parms_match. + (joust): Adjust. + (print_z_candidate): Mark rewritten/reversed candidates. + (build_new_op_1): Warn about recursive call with reversed arguments. + 2019-11-15 Andrew Sutton PR c++/89913 diff --git a/gcc/cp/call.c b/gcc/cp/call.c index 13639a1c901..f4dfa7b3f56 100644 --- a/gcc/cp/call.c +++ b/gcc/cp/call.c @@ -3694,6 +3694,10 @@ print_z_candidate (location_t loc, const char *msgstr, inform (cloc, "%s%#qD (near match)", msg, fn); else if (DECL_DELETED_FN (fn)) inform (cloc, "%s%#qD (deleted)", msg, fn); + else if (candidate->reversed ()) + inform (cloc, "%s%#qD (reversed)", msg, fn); + else if (candidate->rewritten ()) + inform (cloc, "%s%#qD (rewritten)", msg, fn); else inform (cloc, "%s%#qD", msg, fn); if (fn != candidate->fn) @@ -6219,8 +6223,14 @@ build_new_op_1 (const op_location_t &loc, enum tree_code code, int flags, else { if (cand->reversed ()) - /* We swapped these in add_candidate, swap them back now. */ - std::swap (cand->convs[0], cand->convs[1]); + { + /* We swapped these in add_candidate, swap them back now. */ + std::swap (cand->convs[0], cand->convs[1]); + if (cand->fn == current_function_decl) + warning_at (loc, 0, "in C++20 this comparison calls the " + "current function recursively with reversed " + "arguments"); + } result = build_over_call (cand, LOOKUP_NORMAL, complain); } @@ -10995,18 +11005,32 @@ joust_maybe_elide_copy (z_candidate *&cand) return false; } -/* True if cand1 and cand2 represent the same function or function - template. */ +/* True if the defining declarations of the two candidates have equivalent + parameters. */ -static bool -same_fn_or_template (z_candidate *cand1, z_candidate *cand2) +bool +cand_parms_match (z_candidate *c1, z_candidate *c2) { - if (cand1->fn == cand2->fn) + tree fn1 = c1->template_decl; + tree fn2 = c2->template_decl; + if (fn1 && fn2) + { + fn1 = most_general_template (TI_TEMPLATE (fn1)); + fn1 = DECL_TEMPLATE_RESULT (fn1); + fn2 = most_general_template (TI_TEMPLATE (fn2)); + fn2 = DECL_TEMPLATE_RESULT (fn2); + } + else + { + fn1 = c1->fn; + fn2 = c2->fn; + } + if (fn1 == fn2) return true; - if (!cand1->template_decl || !cand2->template_decl) + if (identifier_p (fn1) || identifier_p (fn2)) return false; - return (most_general_template (TI_TEMPLATE (cand1->template_decl)) - == most_general_template (TI_TEMPLATE (cand2->template_decl))); + return compparms (TYPE_ARG_TYPES (TREE_TYPE (fn1)), + TYPE_ARG_TYPES (TREE_TYPE (fn2))); } /* Compare two candidates for overloading as described in @@ -11155,20 +11179,11 @@ joust (struct z_candidate *cand1, struct z_candidate *cand2, bool warn, if (winner && comp != winner) { - if (same_fn_or_template (cand1, cand2)) - { - /* Ambiguity between normal and reversed versions of the - same comparison operator; prefer the normal one. - https://lists.isocpp.org/core/2019/10/7438.php */ - if (cand1->reversed ()) - winner = -1; - else - { - gcc_checking_assert (cand2->reversed ()); - winner = 1; - } - break; - } + /* Ambiguity between normal and reversed comparison operators + with the same parameter types; prefer the normal one. */ + if ((cand1->reversed () != cand2->reversed ()) + && cand_parms_match (cand1, cand2)) + return cand1->reversed () ? -1 : 1; winner = 0; goto tweak; diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite2.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite2.C new file mode 100644 index 00000000000..4f3d12757ff --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite2.C @@ -0,0 +1,12 @@ +// Test that C++20 overload changes don't break sloppy code. + +struct C { + bool operator==(const C&); + bool operator!=(const C&); +}; + +int main() { + C c1, c2; + (void)(c1 == c2); + (void)(c1 != c2); +} diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite3.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite3.C new file mode 100644 index 00000000000..ef29cffbd0b --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite3.C @@ -0,0 +1,10 @@ +// Test that very different operators still cause ambiguity with reversed. + +struct X { operator int(); }; +bool operator==(X, int); // #1 { dg-message "reversed" "" { target c++2a } } +struct Y { operator int(); }; +bool operator==(Y, int); // #2 { dg-message "reversed" "" { target c++2a } } + +X x; Y y; +bool b1 = x == y; // { dg-error "ambiguous" "" { target c++2a } } +bool b2 = y == x; // { dg-error "ambiguous" "" { target c++2a } } diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite4.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite4.C new file mode 100644 index 00000000000..c068b5ab294 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-rewrite4.C @@ -0,0 +1,12 @@ +// { dg-do compile { target c++11 } } + +struct iterator; +struct const_iterator { + const_iterator(const iterator&); + bool operator==(const const_iterator &ci) const = delete; +}; +struct iterator { + bool operator==(const const_iterator &ci) const { + return ci == *this; // { dg-error "deleted" "" { target c++17_down } } + } // { dg-warning "reversed" "" { target c++2a } .-1 } +}; -- 2.30.2