On 9/4/24 11:02 AM, Marek Polacek wrote:
+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);
You don't need this check I think; if the # of args isn't correct, we
should not get here. Then the goto can...go too.
Dropped.
On 9/4/24 11:28 AM, Eric Gallager wrote:
>
> Question about PR tagging: should PR c++/81665 be tagged here, too?
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81665
Added.
Here's what I'm pushing:
From 1914ca8791ce4e0ba821e818cb6f86c76afdb6f2 Mon Sep 17 00:00:00 2001
From: Jason Merrill <ja...@redhat.com>
Date: Thu, 29 Aug 2024 11:09:21 -0400
Subject: [PATCH] c-family: add attribute flag_enum [PR81665]
To: gcc-patches@gcc.gnu.org
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
PR c++/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 | 30 +++++++++++++++
gcc/c-family/c-warn.cc | 4 ++
gcc/testsuite/c-c++-common/attr-flag-enum-1.c | 37 +++++++++++++++++++
9 files changed, 88 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 ebfa6779bec..af0c45b42e0 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -9191,6 +9191,13 @@ 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 0f9b1bab19f..019e0a5ca80 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 79303518dcb..4dd2eecbea5 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.
@@ -5025,6 +5039,22 @@ 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 ARG_UNUSED (args), int ARG_UNUSED (flags),
+ bool *no_add_attrs)
+{
+ if (TREE_CODE (*node) != ENUMERAL_TYPE)
+ {
+ warning (OPT_Wattributes, "%qE attribute ignored on non-enum", name);
+ *no_add_attrs = true;
+ }
+
+ 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:;
+ }
+}
--
2.46.0
