On 11/9/20 12:05 PM, Marek Polacek wrote:
On Fri, Nov 06, 2020 at 03:01:56PM -0500, Jason Merrill via Gcc-patches wrote:
On 11/6/20 2:34 PM, Marek Polacek wrote:
On Fri, Nov 06, 2020 at 02:23:10PM -0500, Jason Merrill via Gcc-patches wrote:
On 11/6/20 2:06 PM, Marek Polacek wrote:
Following Joseph's change for C to allow duplicate C2x standard attributes
<https://gcc.gnu.org/pipermail/gcc-patches/2020-October/557272.html>,
this patch does a similar thing for C++. This is DR 1914, to be resolved by
<wg21.link/p2156>, which is not part of the standard yet, but has a wide
support so look like a shoo-in. Some duplications still produce warnings;
I didn't change that because a warning might be desirable.
What's the rationale for warning about some and not others?
I don't have any. Joseph's patch removed the error for a duplicated
'fallthrough' attribute, but the warning remained so I left it as-is
too.
So either we just downgrade the error to a warning, or remove the
remaining warnings too. I think I slightly prefer the former; with perhaps
a small tweak not to warn when the duplicated attribute comes from a macro
expansion.
Sounds good.
Here's a patch that does that. cp_parser_check_std_attribute now handles
more standard attributes. There's still a discrepancy that we warn about
[[fallthrough]] [[fallthrough]] but not about [[noreturn]] [[noreturn]].
Fixing this would involve calling cp_parser_check_std_attribute in another
spot (in a loop), presumably. But I suspect that's less important for now.
Thanks,
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
Following Joseph's change for C to allow duplicate C2x standard attributes
<https://gcc.gnu.org/pipermail/gcc-patches/2020-October/557272.html>,
this patch does a similar thing for C++. This is DR 1914, to be resolved by
<wg21.link/p2156>, which is not part of the standard yet, but has wide
support so looks like a shoo-in. The duplications now produce warnings
instead, but only if the attribute wasn't specified via a macro.
gcc/c-family/ChangeLog:
DR 1914
* c-common.c (attribute_fallthrough_p): Tweak the warning
message.
gcc/cp/ChangeLog:
DR 1914
* parser.c (cp_parser_check_std_attribute): Return bool. Add a
location_t parameter. Return true if the attribute wasn't duplicated.
Give a warning instead of an error. Check more attributes.
(cp_parser_std_attribute_list): Don't add duplicated attributes to
the list. Pass location to cp_parser_check_std_attribute.
gcc/testsuite/ChangeLog:
DR 1914
* c-c++-common/attr-fallthrough-2.c: Adjust dg-warning.
* g++.dg/cpp0x/fallthrough2.C: Likewise.
* g++.dg/cpp0x/gen-attrs-60.C: Turn dg-error into dg-warning.
* g++.dg/cpp1y/attr-deprecated-2.C: Likewise.
* g++.dg/cpp2a/attr-likely2.C: Adjust dg-warning.
* g++.dg/cpp2a/nodiscard-once.C: Turn dg-error into dg-warning.
* g++.dg/cpp0x/gen-attrs-72.C: New test.
---
gcc/c-family/c-common.c | 5 +-
gcc/cp/parser.c | 51 ++++++++++---------
.../c-c++-common/attr-fallthrough-2.c | 2 +-
gcc/testsuite/g++.dg/cpp0x/fallthrough2.C | 2 +-
gcc/testsuite/g++.dg/cpp0x/gen-attrs-60.C | 2 +-
gcc/testsuite/g++.dg/cpp0x/gen-attrs-72.C | 45 ++++++++++++++++
.../g++.dg/cpp1y/attr-deprecated-2.C | 2 +-
gcc/testsuite/g++.dg/cpp2a/attr-likely2.C | 2 +-
gcc/testsuite/g++.dg/cpp2a/nodiscard-once.C | 2 +-
9 files changed, 81 insertions(+), 32 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/gen-attrs-72.C
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index d4d3228b8f6..29508bca97b 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -5752,9 +5752,10 @@ attribute_fallthrough_p (tree attr)
tree t = lookup_attribute ("fallthrough", attr);
if (t == NULL_TREE)
return false;
- /* This attribute shall appear at most once in each attribute-list. */
+ /* It is no longer true that "this attribute shall appear at most once in
+ each attribute-list", but we still give a warning. */
if (lookup_attribute ("fallthrough", TREE_CHAIN (t)))
- warning (OPT_Wattributes, "%<fallthrough%> attribute specified multiple "
+ warning (OPT_Wattributes, "attribute %<fallthrough%> specified multiple "
"times");
/* No attribute-argument-clause shall be present. */
else if (TREE_VALUE (t) != NULL_TREE)
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 323d7424a83..6fcee3efe6f 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -27269,30 +27269,30 @@ cp_parser_std_attribute (cp_parser *parser, tree
attr_ns)
return attribute;
}
-/* Check that the attribute ATTRIBUTE appears at most once in the
- attribute-list ATTRIBUTES. This is enforced for noreturn (7.6.3),
- nodiscard, and deprecated (7.6.5). Note that
- carries_dependency (7.6.4) isn't implemented yet in GCC. */
+/* Warn if the attribute ATTRIBUTE appears more than once in the
+ attribute-list ATTRIBUTES. This used to be enforced for certain
+ attributes, but the restriction was removed in P2156. Note that
+ carries_dependency ([dcl.attr.depend]) isn't implemented yet in GCC.
+ LOC is the location of ATTRIBUTE. Returns true if ATTRIBUTE was not
+ found in ATTRIBUTES. */
-static void
-cp_parser_check_std_attribute (tree attributes, tree attribute)
+static bool
+cp_parser_check_std_attribute (location_t loc, tree attributes, tree attribute)
{
+ static auto alist = { "noreturn", "deprecated", "nodiscard", "maybe_unused",
+ "likely", "unlikely", "fallthrough",
+ "no_unique_address" };
if (attributes)
- {
- tree name = get_attribute_name (attribute);
- if (is_attribute_p ("noreturn", name)
- && lookup_attribute ("noreturn", attributes))
- error ("attribute %<noreturn%> can appear at most once "
- "in an attribute-list");
- else if (is_attribute_p ("deprecated", name)
- && lookup_attribute ("deprecated", attributes))
- error ("attribute %<deprecated%> can appear at most once "
- "in an attribute-list");
- else if (is_attribute_p ("nodiscard", name)
- && lookup_attribute ("nodiscard", attributes))
- error ("attribute %<nodiscard%> can appear at most once "
- "in an attribute-list");
- }
+ for (const auto &a : alist)
+ if (is_attribute_p (a, get_attribute_name (attribute))
+ && lookup_attribute (a, attributes))
+ {
+ if (!from_macro_expansion_at (loc))
+ warning_at (loc, OPT_Wattributes, "attribute %qs specified "
+ "multiple times", a);
+ return false;
+ }
+ return true;
}
/* Parse a list of standard C++-11 attributes.
@@ -27312,14 +27312,17 @@ cp_parser_std_attribute_list (cp_parser *parser, tree
attr_ns)
while (true)
{
+ location_t loc = cp_lexer_peek_token (parser->lexer)->location;
attribute = cp_parser_std_attribute (parser, attr_ns);
if (attribute == error_mark_node)
break;
if (attribute != NULL_TREE)
{
- cp_parser_check_std_attribute (attributes, attribute);
- TREE_CHAIN (attribute) = attributes;
- attributes = attribute;
+ if (cp_parser_check_std_attribute (loc, attributes, attribute))
You might combine this condition with the enclosing one. OK either way.
+ {
+ TREE_CHAIN (attribute) = attributes;
+ attributes = attribute;
+ }
}
token = cp_lexer_peek_token (parser->lexer);
if (token->type == CPP_ELLIPSIS)
diff --git a/gcc/testsuite/c-c++-common/attr-fallthrough-2.c
b/gcc/testsuite/c-c++-common/attr-fallthrough-2.c
index be61d5e6666..156b413db7a 100644
--- a/gcc/testsuite/c-c++-common/attr-fallthrough-2.c
+++ b/gcc/testsuite/c-c++-common/attr-fallthrough-2.c
@@ -34,7 +34,7 @@ fn (int i)
__attribute__((fallthrough ("x"))); /* { dg-warning "specified with a
parameter" } */
case 7:
bar (1);
- __attribute__((fallthrough, fallthrough)); /* { dg-warning "attribute specified
multiple times" } */
+ __attribute__((fallthrough, fallthrough)); /* { dg-warning "specified multiple
times" } */
case 8:
bar (1);
__attribute__((fallthrough));
diff --git a/gcc/testsuite/g++.dg/cpp0x/fallthrough2.C
b/gcc/testsuite/g++.dg/cpp0x/fallthrough2.C
index f2d0ce1c693..071c2cb09eb 100644
--- a/gcc/testsuite/g++.dg/cpp0x/fallthrough2.C
+++ b/gcc/testsuite/g++.dg/cpp0x/fallthrough2.C
@@ -14,7 +14,7 @@ f (int i)
[[fallthrough]];
case 3:
bar (1);
- [[gnu::fallthrough, gnu::fallthrough]]; // { dg-warning ".fallthrough.
attribute specified multiple times" }
+ [[gnu::fallthrough, gnu::fallthrough]]; // { dg-warning ".fallthrough.
specified multiple times" }
case 2:
bar (2);
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-60.C
b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-60.C
index cb0c31ec63f..9203d1dd1bd 100644
--- a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-60.C
+++ b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-60.C
@@ -1,4 +1,4 @@
// PR c++/60365
// { dg-do compile { target c++11 } }
-void func [[noreturn, noreturn]] (); // { dg-error "at most once" }
+void func [[noreturn, noreturn]] (); // { dg-warning "specified multiple
times" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-72.C
b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-72.C
new file mode 100644
index 00000000000..3c235b5e921
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-72.C
@@ -0,0 +1,45 @@
+// DR 1914 - Duplicate standard attributes
+// { dg-do compile { target c++11 } }
+
+#define ATTR_NORETURN [[noreturn, noreturn]]
+
+[[noreturn, noreturn]] void fn0(); // { dg-warning "specified multiple times" }
+ATTR_NORETURN void fn0a();
+[[noreturn]] [[noreturn]] void fn1();
+[[deprecated, deprecated]] void fn2(); // { dg-warning "specified multiple
times" }
+[[deprecated]] [[deprecated]] void fn3();
+[[maybe_unused]] [[maybe_unused]] int fn4();
+[[maybe_unused, maybe_unused]] int fn5(); // { dg-warning "specified multiple
times" }
+[[nodiscard]] [[nodiscard]] int fn6();
+[[nodiscard, nodiscard]] int fn7(); // { dg-warning "specified multiple times"
}
+
+struct E { };
+struct A {
+ [[no_unique_address]] [[no_unique_address]] E e;
+};
+struct B {
+ [[no_unique_address, no_unique_address]] E e; // { dg-warning "specified multiple
times" }
+};
+
+int
+f (int n)
+{
+ switch (n)
+ {
+ case 1:
+ [[fallthrough, fallthrough]]; // { dg-warning "specified multiple times"
}
+ case 2:
+ [[fallthrough]] [[fallthrough]]; // { dg-warning "specified multiple
times" }
+ case 3:
+ return 15;
+ }
+
+ if (n == 10)
+ [[likely]] [[likely]] return 42; // { dg-warning "ignoring attribute" }
+ else if (n == 11)
+ [[unlikely]] [[unlikely]] return 10; // { dg-warning "ignoring attribute" }
+ else if (n == 12)
+ [[likely, likely]] return 42; // { dg-warning "specified multiple times" }
+ else
+ [[unlikely, unlikely]] return 0; // { dg-warning "specified multiple
times" }
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/attr-deprecated-2.C
b/gcc/testsuite/g++.dg/cpp1y/attr-deprecated-2.C
index 12c75c7ba73..ac6c4aecf9b 100644
--- a/gcc/testsuite/g++.dg/cpp1y/attr-deprecated-2.C
+++ b/gcc/testsuite/g++.dg/cpp1y/attr-deprecated-2.C
@@ -1,4 +1,4 @@
// PR c++/60365
// { dg-do compile { target c++14 } }
-void func [[deprecated, deprecated]] (); // { dg-error "at most once" }
+void func [[deprecated, deprecated]] (); // { dg-warning "specified multiple
times" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/attr-likely2.C
b/gcc/testsuite/g++.dg/cpp2a/attr-likely2.C
index ee178dec9c5..0bc5f1e1ae7 100644
--- a/gcc/testsuite/g++.dg/cpp2a/attr-likely2.C
+++ b/gcc/testsuite/g++.dg/cpp2a/attr-likely2.C
@@ -4,7 +4,7 @@ bool b;
int main()
{
if (b)
- [[likely, likely]] b; // { dg-warning "ignoring" }
+ [[likely, likely]] b; // { dg-warning "specified multiple times" }
else
[[unlikely]] [[likely]] b; // { dg-warning "ignoring" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/nodiscard-once.C b/gcc/testsuite/g++.dg/cpp2a/nodiscard-once.C
index c810fd0daad..c95fa1b0741 100644
--- a/gcc/testsuite/g++.dg/cpp2a/nodiscard-once.C
+++ b/gcc/testsuite/g++.dg/cpp2a/nodiscard-once.C
@@ -2,7 +2,7 @@
/* { dg-do compile { target c++20 } } */
/* { dg-options "-O -ftrack-macro-expansion=0" } */
-[[nodiscard, nodiscard]] int check1 (void); /* { dg-error "nodiscard\[^\n\r]*can appear at most once" } */
+[[nodiscard, nodiscard]] int check1 (void); // { dg-warning "specified multiple
times" }
void
test (void)
base-commit: b642fca1c31b2e2175e0860daf32b4ee0d918085
