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From: Joseph Myers <jsm28@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-2976] c: C2x noreturn attribute Date: Thu, 29 Sep 2022 23:00:09 +0000 (GMT) [thread overview] Message-ID: <20220929230009.0A8D43842423@sourceware.org> (raw) https://gcc.gnu.org/g:3a3516bc4a0a0307cd48dce044a497e95816c8f5 commit r13-2976-g3a3516bc4a0a0307cd48dce044a497e95816c8f5 Author: Joseph Myers <joseph@codesourcery.com> Date: Thu Sep 29 22:59:22 2022 +0000 c: C2x noreturn attribute C2x adds a standard [[noreturn]] attribute (which can also be spelt [[_Noreturn]] for use with <stdnoreturn.h>), so allowing non-returning functions to be declared in a manner compatible with C++; the _Noreturn function specifier remains available but is marked obsolescent. Implement this attribute. It's more restricted than GNU __attribute__ ((noreturn)) - that allows function pointers but using the standard attribute on a function pointer is a constraint violation. Thus, the attribute gets its own handler that checks for a FUNCTION_DECL before calling the handler for the GNU attribute. Tests for the attribute are based on those for C11 _Noreturn and for other C2x attributes. Bootstrapped with no regressions for x86_64-pc-linux-gnu. gcc/c-family/ * c-lex.cc (c_common_has_attribute): Handle noreturn attribute for C. gcc/c/ * c-decl.cc (handle_std_noreturn_attribute): New function. (std_attribute_table): Add _Noreturn and noreturn. gcc/testsuite/ * gcc.dg/c2x-attr-noreturn-1.c, gcc.dg/c2x-attr-noreturn-2.c, gcc.dg/c2x-attr-noreturn-3.c: New tests. * gcc.dg/c2x-has-c-attribute-2.c: Also test __has_c_attribute for noreturn attribute. Diff: --- gcc/c-family/c-lex.cc | 3 ++ gcc/c/c-decl.cc | 25 ++++++++++ gcc/testsuite/gcc.dg/c2x-attr-noreturn-1.c | 56 ++++++++++++++++++++++ gcc/testsuite/gcc.dg/c2x-attr-noreturn-2.c | 72 ++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/c2x-attr-noreturn-3.c | 11 +++++ gcc/testsuite/gcc.dg/c2x-has-c-attribute-2.c | 16 +++++++ 6 files changed, 183 insertions(+) diff --git a/gcc/c-family/c-lex.cc b/gcc/c-family/c-lex.cc index 4d2252fd946..d4e448a0132 100644 --- a/gcc/c-family/c-lex.cc +++ b/gcc/c-family/c-lex.cc @@ -389,6 +389,9 @@ c_common_has_attribute (cpp_reader *pfile, bool std_syntax) result = 202003; else if (is_attribute_p ("maybe_unused", attr_name)) result = 202106; + else if (is_attribute_p ("noreturn", attr_name) + || is_attribute_p ("_Noreturn", attr_name)) + result = 202202; } if (result) attr_name = NULL_TREE; diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc index 740982eae31..bac8e6cc3f6 100644 --- a/gcc/c/c-decl.cc +++ b/gcc/c/c-decl.cc @@ -4480,11 +4480,34 @@ handle_nodiscard_attribute (tree *node, tree name, tree /*args*/, } return NULL_TREE; } + +/* Handle the standard [[noreturn]] attribute. */ + +static tree +handle_std_noreturn_attribute (tree *node, tree name, tree args, + int flags, bool *no_add_attrs) +{ + /* Unlike GNU __attribute__ ((noreturn)), the standard [[noreturn]] + only applies to functions, not function pointers. */ + if (TREE_CODE (*node) == FUNCTION_DECL) + return handle_noreturn_attribute (node, name, args, flags, no_add_attrs); + else + { + pedwarn (input_location, OPT_Wattributes, + "standard %qE attribute can only be applied to functions", + name); + *no_add_attrs = true; + return NULL_TREE; + } +} + /* Table of supported standard (C2x) attributes. */ const struct attribute_spec std_attribute_table[] = { /* { name, min_len, max_len, decl_req, type_req, fn_type_req, affects_type_identity, handler, exclude } */ + { "_Noreturn", 0, 0, false, false, false, false, + handle_std_noreturn_attribute, NULL }, { "deprecated", 0, 1, false, false, false, false, handle_deprecated_attribute, NULL }, { "fallthrough", 0, 0, false, false, false, false, @@ -4493,6 +4516,8 @@ const struct attribute_spec std_attribute_table[] = handle_unused_attribute, NULL }, { "nodiscard", 0, 1, false, false, false, false, handle_nodiscard_attribute, NULL }, + { "noreturn", 0, 0, false, false, false, false, + handle_std_noreturn_attribute, NULL }, { NULL, 0, 0, false, false, false, false, NULL, NULL } }; diff --git a/gcc/testsuite/gcc.dg/c2x-attr-noreturn-1.c b/gcc/testsuite/gcc.dg/c2x-attr-noreturn-1.c new file mode 100644 index 00000000000..d903c09a9e5 --- /dev/null +++ b/gcc/testsuite/gcc.dg/c2x-attr-noreturn-1.c @@ -0,0 +1,56 @@ +/* Test C2x noreturn attribute: valid uses. */ +/* { dg-do compile } */ +/* { dg-options "-std=c2x -pedantic-errors" } */ + +[[noreturn]] void exit (int); + +[[__noreturn__]] int f1 (void); + +[[_Noreturn]] void f2 (void); + +[[___Noreturn__]] static void f3 (void) { exit (0); } + +/* Returning from a noreturn function is undefined at runtime, not a + constraint violation, but recommended practice is to diagnose if + such a return appears possible. */ + +[[noreturn]] int +f4 (void) +{ + return 1; /* { dg-warning "has a 'return' statement" } */ + /* { dg-warning "does return" "second warning" { target *-*-* } .-1 } */ +} + +[[__noreturn__]] void +f5 (void) +{ + return; /* { dg-warning "has a 'return' statement" } */ + /* { dg-warning "does return" "second warning" { target *-*-* } .-1 } */ +} + +[[_Noreturn]] void +f6 (void) +{ +} /* { dg-warning "does return" } */ + +[[___Noreturn__]] void +f7 (int a) +{ + if (a) + exit (0); +} /* { dg-warning "does return" } */ + +/* Declarations need not all have the attribute (buf if the first does not, + there is undefined behavior). */ + +void f2 (void); + +/* Duplicate attribute, and use with _Noreturn, is OK. */ +[[noreturn]] [[noreturn]] [[noreturn, __noreturn__]] void _Noreturn f9 (void); + +/* The attribute does not affect type compatibility. */ + +void (*fp) (void) = f5; + +/* Unlike the function specifier, the attribute may be used on main. */ +[[noreturn]] int main (); diff --git a/gcc/testsuite/gcc.dg/c2x-attr-noreturn-2.c b/gcc/testsuite/gcc.dg/c2x-attr-noreturn-2.c new file mode 100644 index 00000000000..331da4a6b5f --- /dev/null +++ b/gcc/testsuite/gcc.dg/c2x-attr-noreturn-2.c @@ -0,0 +1,72 @@ +/* Test C2x noreturn attribute: invalid contexts. */ +/* { dg-do compile } */ +/* { dg-options "-std=c2x -pedantic-errors" } */ + +[[noreturn]]; /* { dg-error "ignored" } */ + +int [[noreturn]] var; /* { dg-error "ignored" } */ + +int array_with_dep_type[2] [[noreturn]]; /* { dg-error "ignored" } */ + +void fn_with_dep_type () [[noreturn]]; /* { dg-error "ignored" } */ + +int z = sizeof (int [[__noreturn__]]); /* { dg-error "ignored" } */ + +[[noreturn]] int x1; /* { dg-error "can only be applied to functions" } */ +int x2 [[__noreturn__]]; /* { dg-error "can only be applied to functions" } */ + +[[_Noreturn]] void (*fp) (); /* { dg-error "can only be applied to functions" } */ + +void +f (void) +{ + int a; + [[_Noreturn]]; /* { dg-error "ignored" } */ + [[___Noreturn__]] a = 1; /* { dg-error "ignored" } */ +} + +int +g ([[noreturn]] int x, int y) /* { dg-error "can only be applied to functions" } */ +{ + [[noreturn]] typedef float F; /* { dg-error "can only be applied to functions" } */ + [[noreturn]] int a; /* { dg-error "can only be applied to functions" } */ + int b [[__noreturn__]]; /* { dg-error "can only be applied to functions" } */ + int c [[noreturn]]; /* { dg-error "can only be applied to functions" } */ + [[__noreturn__]] label1: ; /* { dg-error "can only be applied to functions" } */ + c = y; + [[noreturn]] label2: ; /* { dg-error "can only be applied to functions" } */ + return y; +} + +struct [[_Noreturn]] s { double d; }; /* { dg-error "can only be applied to functions" } */ + +struct s2 +{ + [[___Noreturn__]] int a; /* { dg-error "can only be applied to functions" } */ + int b [[noreturn]]; /* { dg-error "can only be applied to functions" } */ +} x; + +enum e { E1 [[noreturn]] }; /* { dg-error "can only be applied to functions" } */ + +union [[_Noreturn]] u { int x; }; /* { dg-error "can only be applied to functions" } */ + +enum [[noreturn]] eu { E2 }; /* { dg-error "can only be applied to functions" } */ + +void fx ([[noreturn]] int p); /* { dg-error "can only be applied" } */ + +union u2 +{ + [[noreturn]] int a; /* { dg-error "can only be applied to functions" } */ + int b [[noreturn]]; /* { dg-error "can only be applied to functions" } */ +} y; + +void +g2 (int x) +{ + switch (x) + { + [[noreturn]] case 1: ; /* { dg-error "can only be applied to functions" } */ + [[__noreturn__]] case 2: ; /* { dg-error "can only be applied to functions" } */ + [[noreturn]] default: ; /* { dg-error "can only be applied to functions" } */ + } +} diff --git a/gcc/testsuite/gcc.dg/c2x-attr-noreturn-3.c b/gcc/testsuite/gcc.dg/c2x-attr-noreturn-3.c new file mode 100644 index 00000000000..aaf21e22a13 --- /dev/null +++ b/gcc/testsuite/gcc.dg/c2x-attr-noreturn-3.c @@ -0,0 +1,11 @@ +/* Test C2x noreturn attribute: invalid syntax. */ +/* { dg-do compile } */ +/* { dg-options "-std=c2x -pedantic-errors" } */ + +[[noreturn()]] void a(); /* { dg-error "does not take any arguments" } */ + +[[__noreturn__(0)]] void b(); /* { dg-error "does not take any arguments|expected" } */ + +[[_Noreturn("", 123)]] void c(); /* { dg-error "does not take any arguments|expected" } */ + +[[___Noreturn__("")]] void d(); /* { dg-error "does not take any arguments|expected" } */ diff --git a/gcc/testsuite/gcc.dg/c2x-has-c-attribute-2.c b/gcc/testsuite/gcc.dg/c2x-has-c-attribute-2.c index 6a379e9db4f..3c34ab6cbd9 100644 --- a/gcc/testsuite/gcc.dg/c2x-has-c-attribute-2.c +++ b/gcc/testsuite/gcc.dg/c2x-has-c-attribute-2.c @@ -34,6 +34,22 @@ #error "bad result for __fallthrough__" #endif +#if __has_c_attribute (noreturn) != 202202L +#error "bad result for noreturn" +#endif + +#if __has_c_attribute (__noreturn__) != 202202L +#error "bad result for __noreturn__" +#endif + +#if __has_c_attribute (_Noreturn) != 202202L +#error "bad result for _Noreturn" +#endif + +#if __has_c_attribute (___Noreturn__) != 202202L +#error "bad result for ___Noreturn__" +#endif + /* Macros in the attribute name are expanded. */ #define foo deprecated #if __has_c_attribute (foo) != 201904L
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