From 5f9669d9e23a1116e040c80e0f3d4f43639bda52 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Fri, 31 Jul 2020 23:08:00 +0200 Subject: [PATCH] c++: Use error_at rather than warning_at for missing return in constexpr functions [PR96182] For C++11 we already emit an error if a constexpr function doesn't contain a return statement, because in C++11 that is the only thing it needs to contain, but for C++14 we would normally issue a -Wreturn-type warning. As mentioned by Jonathan, such constexpr functions are invalid, no diagnostics required, because there doesn't exist any arguments for which it would result in valid constant expression. This raises it to an error in such cases. The !LAMBDA_TYPE_P case is to avoid error on g++.dg/pr81194.C where the user didn't write constexpr anywhere and the operator() is compiler generated. 2020-07-31 Jakub Jelinek PR c++/96182 * decl.c (finish_function): In constexpr functions use for C++14 and later error instead of warning if no return statement is present and diagnose it regardless of warn_return_type. Move the warn_return_type diagnostics earlier in the function. * g++.dg/cpp1y/constexpr-96182.C: New test. * g++.dg/other/error35.C (S::g()): Add return statement. * g++.dg/cpp1y/pr63996.C (foo): Likewise. * g++.dg/cpp1y/constexpr-return2.C (f): Likewise. * g++.dg/cpp1y/var-templ44.C (make_array): Add throw 1. --- gcc/cp/decl.c | 83 ++++++++++--------- gcc/testsuite/g++.dg/cpp1y/constexpr-96182.C | 6 ++ .../g++.dg/cpp1y/constexpr-return2.C | 1 + gcc/testsuite/g++.dg/cpp1y/pr63996.C | 1 + gcc/testsuite/g++.dg/cpp1y/var-templ44.C | 1 + gcc/testsuite/g++.dg/other/error35.C | 2 +- 6 files changed, 55 insertions(+), 39 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-96182.C diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c index b4beaa94257..a68bbe04da7 100644 --- a/gcc/cp/decl.c +++ b/gcc/cp/decl.c @@ -17112,6 +17112,51 @@ finish_function (bool inline_p) DECL_ATTRIBUTES (fndecl))) omp_declare_variant_finalize (fndecl, attr); + /* Complain if there's just no return statement. */ + if ((warn_return_type + || (cxx_dialect >= cxx14 + && DECL_DECLARED_CONSTEXPR_P (fndecl))) + && !VOID_TYPE_P (TREE_TYPE (fntype)) + && !dependent_type_p (TREE_TYPE (fntype)) + && !current_function_returns_value && !current_function_returns_null + /* Don't complain if we abort or throw. */ + && !current_function_returns_abnormally + /* Don't complain if there's an infinite loop. */ + && !current_function_infinite_loop + /* Don't complain if we are declared noreturn. */ + && !TREE_THIS_VOLATILE (fndecl) + && !DECL_NAME (DECL_RESULT (fndecl)) + && !TREE_NO_WARNING (fndecl) + /* Structor return values (if any) are set by the compiler. */ + && !DECL_CONSTRUCTOR_P (fndecl) + && !DECL_DESTRUCTOR_P (fndecl) + && targetm.warn_func_return (fndecl)) + { + gcc_rich_location richloc (input_location); + /* Potentially add a "return *this;" fix-it hint for + assignment operators. */ + if (IDENTIFIER_ASSIGN_OP_P (DECL_NAME (fndecl))) + { + tree valtype = TREE_TYPE (DECL_RESULT (fndecl)); + if (TREE_CODE (valtype) == REFERENCE_TYPE + && current_class_ref + && same_type_ignoring_top_level_qualifiers_p + (TREE_TYPE (valtype), TREE_TYPE (current_class_ref)) + && global_dc->option_enabled (OPT_Wreturn_type, + global_dc->lang_mask, + global_dc->option_state)) + add_return_star_this_fixit (&richloc, fndecl); + } + if (cxx_dialect >= cxx14 + && DECL_DECLARED_CONSTEXPR_P (fndecl)) + error_at (&richloc, "no return statement in % function " + "returning non-void"); + else if (warning_at (&richloc, OPT_Wreturn_type, + "no return statement in function returning " + "non-void")) + TREE_NO_WARNING (fndecl) = 1; + } + /* Lambda closure members are implicitly constexpr if possible. */ if (cxx_dialect >= cxx17 && LAMBDA_TYPE_P (CP_DECL_CONTEXT (fndecl))) @@ -17163,44 +17208,6 @@ finish_function (bool inline_p) to the FUNCTION_DECL node itself. */ BLOCK_SUPERCONTEXT (DECL_INITIAL (fndecl)) = fndecl; - /* Complain if there's just no return statement. */ - if (warn_return_type - && !VOID_TYPE_P (TREE_TYPE (fntype)) - && !dependent_type_p (TREE_TYPE (fntype)) - && !current_function_returns_value && !current_function_returns_null - /* Don't complain if we abort or throw. */ - && !current_function_returns_abnormally - /* Don't complain if there's an infinite loop. */ - && !current_function_infinite_loop - /* Don't complain if we are declared noreturn. */ - && !TREE_THIS_VOLATILE (fndecl) - && !DECL_NAME (DECL_RESULT (fndecl)) - && !TREE_NO_WARNING (fndecl) - /* Structor return values (if any) are set by the compiler. */ - && !DECL_CONSTRUCTOR_P (fndecl) - && !DECL_DESTRUCTOR_P (fndecl) - && targetm.warn_func_return (fndecl)) - { - gcc_rich_location richloc (input_location); - /* Potentially add a "return *this;" fix-it hint for - assignment operators. */ - if (IDENTIFIER_ASSIGN_OP_P (DECL_NAME (fndecl))) - { - tree valtype = TREE_TYPE (DECL_RESULT (fndecl)); - if (TREE_CODE (valtype) == REFERENCE_TYPE - && current_class_ref - && same_type_ignoring_top_level_qualifiers_p - (TREE_TYPE (valtype), TREE_TYPE (current_class_ref)) - && global_dc->option_enabled (OPT_Wreturn_type, - global_dc->lang_mask, - global_dc->option_state)) - add_return_star_this_fixit (&richloc, fndecl); - } - if (warning_at (&richloc, OPT_Wreturn_type, - "no return statement in function returning non-void")) - TREE_NO_WARNING (fndecl) = 1; - } - /* Store the end of the function, so that we get good line number info for the epilogue. */ cfun->function_end_locus = input_location; diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-96182.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-96182.C new file mode 100644 index 00000000000..9c07d7186ec --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-96182.C @@ -0,0 +1,6 @@ +// PR c++/96182 +// { dg-do compile { target c++11 } } + +constexpr int foo () {} // { dg-error "no return statement in 'constexpr' function returning non-void" "" { target c++14 } } +// { dg-error "body of 'constexpr' function 'constexpr int foo\\\(\\\)' not a return-statement" "" { target c++11_only } .-1 } +// { dg-warning "no return statement in function returning non-void" "" { target c++11_only } .-2 } diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-return2.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-return2.C index cb0185414af..3357fe3cf23 100644 --- a/gcc/testsuite/g++.dg/cpp1y/constexpr-return2.C +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-return2.C @@ -3,6 +3,7 @@ constexpr int f (int i) { + if (i == -1) return 0; } constexpr int i = f(42); // { dg-error "flows off the end|in .constexpr. expansion of " } diff --git a/gcc/testsuite/g++.dg/cpp1y/pr63996.C b/gcc/testsuite/g++.dg/cpp1y/pr63996.C index fe47544a3c8..8eee2e0af30 100644 --- a/gcc/testsuite/g++.dg/cpp1y/pr63996.C +++ b/gcc/testsuite/g++.dg/cpp1y/pr63996.C @@ -5,6 +5,7 @@ constexpr int foo (int i) { int a[i] = { }; // { dg-error "7:ISO C\\+\\+ forbids variable length array .a" } + if (i == 23) return 0; } constexpr int j = foo (1); // { dg-error "flows off the end|in .constexpr. expansion of" } diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ44.C b/gcc/testsuite/g++.dg/cpp1y/var-templ44.C index 2ef01cf7480..74954ed102c 100644 --- a/gcc/testsuite/g++.dg/cpp1y/var-templ44.C +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ44.C @@ -26,5 +26,6 @@ constexpr auto make_array() -> array, common_type_t<>, _Dest>, sizeof...(_Types)> { static_assert(__or_<__not_>, __and_<>>::value, ""); // { dg-error "static assert" } + throw 1; } auto d = make_array(); diff --git a/gcc/testsuite/g++.dg/other/error35.C b/gcc/testsuite/g++.dg/other/error35.C index e9c8371f18b..063bc4a9680 100644 --- a/gcc/testsuite/g++.dg/other/error35.C +++ b/gcc/testsuite/g++.dg/other/error35.C @@ -9,6 +9,6 @@ template struct S { enum S::E; template enum S::E : int { b }; template -constexpr int S::g() const { b; } // { dg-error "not declared" } +constexpr int S::g() const { b; if (false) return 0; } // { dg-error "not declared" } static_assert(S().g() == 1, ""); // { dg-error "" } // { dg-message "in .constexpr. expansion of" "" { target *-*-* } .-1 } -- 2.30.2