On Wed, Sep 4, 2024 at 8:18 AM Jason Merrill <ja...@redhat.com> wrote: > > Tested x86_64-pc-linux-gnu. Any objections? > > -- 8< -- > > Several PRs complain about -Wswitch warning about a case for a bitwise > combination of enumerators. Clang has an attribute flag_enum to prevent > this; let's adopt that approach as well. > > This also recognizes the attribute as [[clang::flag_enum]], introducing > handling of the clang attribute namespace. > > PR c++/46457
Question about PR tagging: should PR c++/81665 be tagged here, too? https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81665 > > gcc/c-family/ChangeLog: > > * c-attribs.cc (handle_flag_enum_attribute): New. > (c_common_gnu_attributes): Add it. > (c_common_clang_attributes, c_common_clang_attribute_table): New. > * c-common.h: Declare c_common_clang_attribute_table. > * c-warn.cc (c_do_switch_warnings): Handle flag_enum. > > gcc/c/ChangeLog: > > * c-objc-common.h (c_objc_attribute_table): Add > c_common_clang_attribute_table. > > gcc/cp/ChangeLog: > > * cp-objcp-common.h (cp_objcp_attribute_table): Add > c_common_clang_attribute_table. > > gcc/testsuite/ChangeLog: > > * c-c++-common/attr-flag-enum-1.c: New test. > > gcc/ChangeLog: > > * doc/extend.texi: Document flag_enum attribute. > * doc/invoke.texi: Mention flag_enum in -Wswitch. > > libstdc++-v3/ChangeLog: > > * include/bits/regex_constants.h: Use flag_enum. > --- > gcc/doc/extend.texi | 7 ++++ > gcc/doc/invoke.texi | 11 +++--- > gcc/c-family/c-common.h | 1 + > gcc/c/c-objc-common.h | 1 + > gcc/cp/cp-objcp-common.h | 1 + > libstdc++-v3/include/bits/regex_constants.h | 2 +- > gcc/c-family/c-attribs.cc | 33 +++++++++++++++++ > gcc/c-family/c-warn.cc | 4 ++ > gcc/testsuite/c-c++-common/attr-flag-enum-1.c | 37 +++++++++++++++++++ > 9 files changed, 91 insertions(+), 6 deletions(-) > create mode 100644 gcc/testsuite/c-c++-common/attr-flag-enum-1.c > > diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi > index 5845bcedf6e..5b9d8c51059 100644 > --- a/gcc/doc/extend.texi > +++ b/gcc/doc/extend.texi > @@ -9187,6 +9187,13 @@ initialization will result in future breakage. > GCC emits warnings based on this attribute by default; use > @option{-Wno-designated-init} to suppress them. > > +@cindex @code{flag_enum} type attribute > +@item flag_enum > +This attribute may be applied to an enumerated type to indicate that > +its enumerators are used in bitwise operations, so e.g. @option{-Wswitch} > +should not warn about a @code{case} that corresponds to a bitwise > +combination of enumerators. > + > @cindex @code{hardbool} type attribute > @item hardbool > @itemx hardbool (@var{false_value}) > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > index 43afb0984e5..7c6175efbc0 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -7672,9 +7672,9 @@ unless C++14 mode (or newer) is active. > Warn whenever a @code{switch} statement has an index of enumerated type > and lacks a @code{case} for one or more of the named codes of that > enumeration. (The presence of a @code{default} label prevents this > -warning.) @code{case} labels outside the enumeration range also > -provoke warnings when this option is used (even if there is a > -@code{default} label). > +warning.) @code{case} labels that do not correspond to enumerators also > +provoke warnings when this option is used, unless the enumeration is marked > +with the @code{flag_enum} attribute. > This warning is enabled by @option{-Wall}. > > @opindex Wswitch-default > @@ -7688,8 +7688,9 @@ case. > @item -Wswitch-enum > Warn whenever a @code{switch} statement has an index of enumerated type > and lacks a @code{case} for one or more of the named codes of that > -enumeration. @code{case} labels outside the enumeration range also > -provoke warnings when this option is used. The only difference > +enumeration. @code{case} labels that do not correspond to enumerators also > +provoke warnings when this option is used, unless the enumeration is marked > +with the @code{flag_enum} attribute. The only difference > between @option{-Wswitch} and this option is that this option gives a > warning about an omitted enumeration code even if there is a > @code{default} label. > diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h > index d3827573a36..027f077d51b 100644 > --- a/gcc/c-family/c-common.h > +++ b/gcc/c-family/c-common.h > @@ -821,6 +821,7 @@ extern struct visibility_flags visibility_options; > > /* Attribute table common to the C front ends. */ > extern const struct scoped_attribute_specs c_common_gnu_attribute_table; > +extern const struct scoped_attribute_specs c_common_clang_attribute_table; > extern const struct scoped_attribute_specs c_common_format_attribute_table; > > /* Pointer to function to lazily generate the VAR_DECL for __FUNCTION__ etc. > diff --git a/gcc/c/c-objc-common.h b/gcc/c/c-objc-common.h > index 20af5a5bb94..365b5938803 100644 > --- a/gcc/c/c-objc-common.h > +++ b/gcc/c/c-objc-common.h > @@ -79,6 +79,7 @@ static const scoped_attribute_specs *const > c_objc_attribute_table[] = > { > &std_attribute_table, > &c_common_gnu_attribute_table, > + &c_common_clang_attribute_table, > &c_common_format_attribute_table > }; > > diff --git a/gcc/cp/cp-objcp-common.h b/gcc/cp/cp-objcp-common.h > index 0e6664cf9c3..e9c5ac40020 100644 > --- a/gcc/cp/cp-objcp-common.h > +++ b/gcc/cp/cp-objcp-common.h > @@ -128,6 +128,7 @@ static const scoped_attribute_specs *const > cp_objcp_attribute_table[] = > &std_attribute_table, > &cxx_gnu_attribute_table, > &c_common_gnu_attribute_table, > + &c_common_clang_attribute_table, > &c_common_format_attribute_table > }; > > diff --git a/libstdc++-v3/include/bits/regex_constants.h > b/libstdc++-v3/include/bits/regex_constants.h > index 437895f1dc3..4148093bc4e 100644 > --- a/libstdc++-v3/include/bits/regex_constants.h > +++ b/libstdc++-v3/include/bits/regex_constants.h > @@ -66,7 +66,7 @@ namespace regex_constants > * elements @c ECMAScript, @c basic, @c extended, @c awk, @c grep, @c egrep > * %set. > */ > - enum syntax_option_type : unsigned int > + enum [[gnu::flag_enum]] syntax_option_type : unsigned int > { > _S_icase = 1 << 0, > _S_nosubs = 1 << 1, > diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc > index cf27cd6d521..f3cf66ffb85 100644 > --- a/gcc/c-family/c-attribs.cc > +++ b/gcc/c-family/c-attribs.cc > @@ -184,6 +184,7 @@ static tree handle_signed_bool_precision_attribute (tree > *, tree, tree, int, > static tree handle_hardbool_attribute (tree *, tree, tree, int, bool *); > static tree handle_retain_attribute (tree *, tree, tree, int, bool *); > static tree handle_fd_arg_attribute (tree *, tree, tree, int, bool *); > +static tree handle_flag_enum_attribute (tree *, tree, tree, int, bool *); > static tree handle_null_terminated_string_arg_attribute (tree *, tree, tree, > int, bool *); > > /* Helper to define attribute exclusions. */ > @@ -631,6 +632,8 @@ const struct attribute_spec c_common_gnu_attributes[] = > handle_fd_arg_attribute, NULL}, > { "fd_arg_write", 1, 1, false, true, true, false, > handle_fd_arg_attribute, NULL}, > + { "flag_enum", 0, 0, false, true, false, false, > + handle_flag_enum_attribute, NULL }, > { "null_terminated_string_arg", 1, 1, false, true, true, false, > handle_null_terminated_string_arg_attribute, > NULL} > }; > @@ -640,6 +643,17 @@ const struct scoped_attribute_specs > c_common_gnu_attribute_table = > "gnu", { c_common_gnu_attributes } > }; > > +/* Attributes also recognized in the clang:: namespace. */ > +const struct attribute_spec c_common_clang_attributes[] = { > + { "flag_enum", 0, 0, false, true, false, false, > + handle_flag_enum_attribute, NULL } > +}; > + > +const struct scoped_attribute_specs c_common_clang_attribute_table = > +{ > + "clang", { c_common_clang_attributes } > +}; > + > /* Give the specifications for the format attributes, used by C and all > descendants. > > @@ -5017,6 +5031,25 @@ handle_fd_arg_attribute (tree *node, tree name, tree > args, > return NULL_TREE; > } > > +/* Handle the "flag_enum" attribute. */ > + > +static tree > +handle_flag_enum_attribute (tree *node, tree ARG_UNUSED(name), tree args, > + int ARG_UNUSED (flags), bool *no_add_attrs) > +{ > + if (args) > + warning (OPT_Wattributes, "%qE attribute arguments ignored", name); > + else if (TREE_CODE (*node) != ENUMERAL_TYPE) > + warning (OPT_Wattributes, "%qE attribute ignored on non-enum", name); > + else > + goto ok; > + > + *no_add_attrs = true; > + > + ok: > + return NULL_TREE; > +} > + > /* Handle the "null_terminated_string_arg" attribute. */ > > static tree > diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc > index 5e4fb7f0f0a..47e0a6bfa07 100644 > --- a/gcc/c-family/c-warn.cc > +++ b/gcc/c-family/c-warn.cc > @@ -1808,6 +1808,10 @@ c_do_switch_warnings (splay_tree cases, location_t > switch_location, > TREE_PURPOSE (chain)); > } > > + /* Attribute flag_enum means bitwise combinations are OK. */ > + if (lookup_attribute ("flag_enum", TYPE_ATTRIBUTES (type))) > + return; > + > /* Warn if there are case expressions that don't correspond to > enumerators. This can occur since C and C++ don't enforce > type-checking of assignments to enumeration variables. > diff --git a/gcc/testsuite/c-c++-common/attr-flag-enum-1.c > b/gcc/testsuite/c-c++-common/attr-flag-enum-1.c > new file mode 100644 > index 00000000000..4eb78b1d8ee > --- /dev/null > +++ b/gcc/testsuite/c-c++-common/attr-flag-enum-1.c > @@ -0,0 +1,37 @@ > +/* { dg-additional-options -Wswitch } */ > + > +enum E0 { a0 = 1, b0 = 2 }; > +void f0 (enum E0 e) { > + switch (e) { > + case !(a0|b0): /* { dg-warning "not in enumerated type" } */ > + case a0|b0: /* { dg-warning "not in enumerated type" } */ > + default:; > + } > +} > + > +enum __attribute ((flag_enum)) E1 { a1 = 1, b1 = 2 }; > +void f1 (enum E1 e) { > + switch (e) { > + case !(a1|b1): /* { dg-bogus "not in enumerated type" } */ > + case a1|b1: /* { dg-bogus "not in enumerated type" } */ > + default:; > + } > +} > + > +enum [[gnu::flag_enum]] E2 { a2 = 1, b2 = 2 }; > +void f2 (enum E2 e) { > + switch (e) { > + case !(a2|b2): /* { dg-bogus "not in enumerated type" } */ > + case a2|b2: /* { dg-bogus "not in enumerated type" } */ > + default:; > + } > +} > + > +enum [[clang::flag_enum]] E3 { a3 = 1, b3 = 2 }; > +void f3 (enum E3 e) { > + switch (e) { > + case !(a3|b3): /* { dg-bogus "not in enumerated type" } */ > + case a3|b3: /* { dg-bogus "not in enumerated type" } */ > + default:; > + } > +} > > base-commit: 3775f71c8909b3531fe002138814fa2504ec2e8b > -- > 2.46.0 >
