From 97cc11871e39888bfca4ed4bf09fa09fe0916266 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Fri, 15 Nov 2019 18:39:35 +0000 Subject: [PATCH] Support C2x [[maybe_unused]] attribute. This patch adds support for the C2x [[maybe_unused]] attribute, using the same handler as for GNU __attribute__ ((unused)). As with other such attribute support, I think turning certain warnings into pedwarns for usage in cases where that is a constraint violation can be addressed later as a bug fix, as can the C2x constraint for various standard attributes that they do not appear more than once inside a single [[]]. However, the warnings that appear in c2x-attr-maybe_unused-1.c (that the attribute is ignored on member declarations) need to remain as warnings not pedwarns, since C2x does permit the attribute there. (Or they could be silenced, on the basis that GCC doesn't have warnings for unused struct and union members so it's completely harmless that it's ignoring an attribute that might do something useful with another compiler that does have such warnings.) Bootstrapped with no regressions on x86_64-pc-linux-gnu. gcc/c: * c-decl.c (std_attribute_table): Add maybe_unused. gcc/testsuite: * gcc.dg/c2x-attr-maybe_unused-1.c, gcc.dg/c2x-attr-maybe_unused-2.c, gcc.dg/c2x-attr-maybe_unused-3.c: New tests. From-SVN: r278310 --- gcc/c/ChangeLog | 4 +++ gcc/c/c-decl.c | 2 ++ gcc/testsuite/ChangeLog | 6 ++++ .../gcc.dg/c2x-attr-maybe_unused-1.c | 31 +++++++++++++++++++ .../gcc.dg/c2x-attr-maybe_unused-2.c | 25 +++++++++++++++ .../gcc.dg/c2x-attr-maybe_unused-3.c | 11 +++++++ 6 files changed, 79 insertions(+) create mode 100644 gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-1.c create mode 100644 gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-2.c create mode 100644 gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-3.c diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog index c2cab579838..75a44e28927 100644 --- a/gcc/c/ChangeLog +++ b/gcc/c/ChangeLog @@ -1,3 +1,7 @@ +2019-11-15 Joseph Myers + + * c-decl.c (std_attribute_table): Add maybe_unused. + 2019-11-15 Joseph Myers * c-decl.c (std_attribute_table): Add fallthrough. diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c index 98b71ea620b..cb6169c4642 100644 --- a/gcc/c/c-decl.c +++ b/gcc/c/c-decl.c @@ -4345,6 +4345,8 @@ const struct attribute_spec std_attribute_table[] = handle_deprecated_attribute, NULL }, { "fallthrough", 0, 0, false, false, false, false, handle_fallthrough_attribute, NULL }, + { "maybe_unused", 0, 0, false, false, false, false, + handle_unused_attribute, NULL }, { NULL, 0, 0, false, false, false, false, NULL, NULL } }; diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index b835d671eba..8473e7a219e 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,9 @@ +2019-11-15 Joseph Myers + + * gcc.dg/c2x-attr-maybe_unused-1.c, + gcc.dg/c2x-attr-maybe_unused-2.c, + gcc.dg/c2x-attr-maybe_unused-3.c: New tests. + 2019-11-15 Matthew Malcomson * gcc.dg/rtl/aarch64/rtl-handle-column-numbers.c: New test. diff --git a/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-1.c b/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-1.c new file mode 100644 index 00000000000..221ebdd19b8 --- /dev/null +++ b/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-1.c @@ -0,0 +1,31 @@ +/* Test C2x maybe_unused attribute: valid uses. */ +/* { dg-do compile } */ +/* { dg-options "-std=c2x -pedantic-errors -Wall -Wextra -Wunused" } */ + +[[maybe_unused]] static void f1 (void) {} + +[[__maybe_unused__]] const int c1 = 1; +static int c2 [[maybe_unused]] = 2; + +int +g ([[maybe_unused]] int x, int y) +{ + [[maybe_unused]] typedef float F; + [[maybe_unused]] int a; + int b [[__maybe_unused__]]; + int c [[maybe_unused]]; + c = y; + return y; +} + +struct [[maybe_unused]] s { double d; }; + +struct s2 { [[__maybe_unused__]] int a; int b [[maybe_unused]]; } x; /* { dg-warning "attribute ignored" } */ + +enum e { E1 [[maybe_unused]] }; + +union [[maybe_unused]] u { int x; }; + +enum [[maybe_unused]] eu { E2 }; + +union u2 { [[maybe_unused]] int a; int b [[maybe_unused]]; } y; /* { dg-warning "attribute ignored" } */ diff --git a/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-2.c b/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-2.c new file mode 100644 index 00000000000..9b5055bad48 --- /dev/null +++ b/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-2.c @@ -0,0 +1,25 @@ +/* Test C2x maybe_unused attribute: invalid contexts. */ +/* { dg-do compile } */ +/* { dg-options "-std=c2x -pedantic-errors" } */ + +/* This attribute is not valid in most cases on types other than their + definitions, or on statements, or as an attribute-declaration. */ + +[[maybe_unused]]; /* { dg-warning "ignored" } */ + +int [[maybe_unused]] var; /* { dg-warning "ignored" } */ +/* { dg-message "that appertains to a type-specifier" "appertains" { target *-*-* } .-1 } */ + +int array_with_dep_type[2] [[maybe_unused]]; /* { dg-warning "ignored" } */ +/* { dg-message "that appertains to a type-specifier" "appertains" { target *-*-* } .-1 } */ + +void fn_with_dep_type () [[maybe_unused]]; /* { dg-warning "ignored" } */ +/* { dg-message "that appertains to a type-specifier" "appertains" { target *-*-* } .-1 } */ + +void +f (void) +{ + int a; + [[maybe_unused]]; /* { dg-warning "ignored" } */ + [[maybe_unused]] a = 1; /* { dg-warning "ignored" } */ +} diff --git a/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-3.c b/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-3.c new file mode 100644 index 00000000000..4d4da0867c2 --- /dev/null +++ b/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-3.c @@ -0,0 +1,11 @@ +/* Test C2x maybe_unused attribute: invalid syntax. */ +/* { dg-do compile } */ +/* { dg-options "-std=c2x -pedantic-errors" } */ + +[[maybe_unused()]] int a; /* { dg-error "does not take any arguments" } */ + +[[maybe_unused(0)]] int b; /* { dg-error "does not take any arguments|expected" } */ + +[[maybe_unused("", 123)]] int c; /* { dg-error "does not take any arguments|expected" } */ + +[[maybe_unused("")]] int d; /* { dg-error "does not take any arguments|expected" } */ -- 2.30.2