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The `[[carries_dependency]]` attribute was added to the standard in C++11, but
implementations have (uniformly, as best I can tell) been ignoring this
attribute for the past decade. In Clang, we would parse the attribute and
otherwise do nothing useful with it (no additional analyses, no communication
of the attribute to the backend, etc). As far as I know, we have no future
plans to implement the semantics of the attribute. However,
`__has_cpp_attribute(carries_dependency)` returns a nonzero value which
suggests we actually do support the attribute and do useful things with it,
especially because we documented that it might improve performance.
This removes all support for `[[carries_dependency]]` and treats it as an
unknown attribute instead (the same as we do for other standard attributes we
don't support, like `[[no_unique_address]]` on some targets). We now return
zero from `__has_cpp_attribute(carries_dependency)`, which matches the behavior
of GCC.
I can find no evidence of user code that should be impacted by this. All uses
of the GNU version of the attribute were in compiler test suites:
https://sourcegraph.com/search?q=context:global+__attribute__%28%28carries_dependency%29%29+-file:.*test.*+-file:clang&patternType=standard&sm=1&groupBy=repo
All uses of the C++ version of the attribute are also in compiler
implementations or documentation:
https://sourcegraph.com/search?q=context:global+%5B%5Bcarries_dependency%5D%5D+-file:.*test.*+-file:clang&patternType=standard&sm=1&groupBy=repo
Incidentally, this also helps people in WG21 build a case for deprecating and
removing this attribute in a future revision of C++.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D143670
Files:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/lib/Parse/ParseDeclCXX.cpp
clang/lib/Sema/SemaDecl.cpp
clang/lib/Sema/SemaDeclAttr.cpp
clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p1.cpp
clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p2.cpp
clang/test/CodeCompletion/attr.cpp
clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/Parser/cxx0x-attributes.cpp
clang/test/Parser/cxx11-stmt-attributes.cpp
clang/test/Parser/stmt-attributes.c
clang/test/Preprocessor/has_attribute.cpp
clang/test/SemaCXX/attr-cxx0x.cpp
Index: clang/test/SemaCXX/attr-cxx0x.cpp
===================================================================
--- clang/test/SemaCXX/attr-cxx0x.cpp
+++ clang/test/SemaCXX/attr-cxx0x.cpp
@@ -46,7 +46,7 @@
static_assert(alignof(int(int)) >= 1, "alignof(function) not positive"); // expected-error{{invalid application of 'alignof' to a function type}}
-[[__carries_dependency__]]
+[[__carries_dependency__]] // expected-warning {{unknown attribute '__carries_dependency__' ignored}}
void func(void);
alignas(4) auto PR19252 = 0;
Index: clang/test/Preprocessor/has_attribute.cpp
===================================================================
--- clang/test/Preprocessor/has_attribute.cpp
+++ clang/test/Preprocessor/has_attribute.cpp
@@ -2,6 +2,7 @@
// RUN: %clang_cc1 -triple i386-windows -fms-compatibility -std=c++11 -E -P %s -o - | FileCheck %s --check-prefixes=CHECK,WINDOWS --implicit-check-not=:
#define CXX11(x) x: __has_cpp_attribute(x)
+#define NOT_SUPPORTED(x) x: __has_cpp_attribute(x)
// CHECK: clang::fallthrough: 201603L
CXX11(clang::fallthrough)
@@ -35,7 +36,7 @@
// Test for standard attributes as listed in C++2a [cpp.cond] paragraph 6.
CXX11(assert)
-CXX11(carries_dependency)
+NOT_SUPPORTED(carries_dependency)
CXX11(deprecated)
CXX11(ensures)
CXX11(expects)
@@ -47,7 +48,7 @@
CXX11(noreturn)
CXX11(unlikely)
// FIXME(201806L) CHECK: assert: 0
-// CHECK: carries_dependency: 200809L
+// CHECK: carries_dependency: 0
// CHECK: deprecated: 201309L
// FIXME(201806L) CHECK: ensures: 0
// FIXME(201806L) CHECK: expects: 0
Index: clang/test/Parser/stmt-attributes.c
===================================================================
--- clang/test/Parser/stmt-attributes.c
+++ clang/test/Parser/stmt-attributes.c
@@ -41,7 +41,7 @@
__attribute__((unused)) switch (i) { // expected-error {{'unused' attribute cannot be applied to a statement}}
__attribute__((uuid)) case 0: // expected-warning {{unknown attribute 'uuid' ignored}}
__attribute__((visibility(""))) default: // expected-error {{'visibility' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) break; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) break; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
}
__attribute__((fastcall)) goto there; // expected-error {{'fastcall' attribute cannot be applied to a statement}}
@@ -49,26 +49,26 @@
__attribute__((weakref)) return; // expected-error {{'weakref' attribute only applies to variables and functions}}
- __attribute__((carries_dependency)); // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) {} // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) if (0) {} // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) for (;;); // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) do { // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) continue; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}} ignored}}
+ __attribute__((nonnull)); // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) {} // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) if (0) {} // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) for (;;); // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) do { // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) continue; // expected-error {{'nonnull' attribute cannot be applied to a statement}} ignored}}
}
while (0)
;
- __attribute__((carries_dependency)) while (0); // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) while (0); // expected-error {{'nonnull' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) switch (i) { // expected-error {{'carries_dependency' attribute cannot be applied to a statement}} ignored}}
- __attribute__((carries_dependency)) case 0: // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) default: // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) break; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) switch (i) { // expected-error {{'nonnull' attribute cannot be applied to a statement}} ignored}}
+ __attribute__((nonnull)) case 0: // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) default: // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) break; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
}
- __attribute__((carries_dependency)) goto here; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) goto here; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
- __attribute__((carries_dependency)) return; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ __attribute__((nonnull)) return; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
}
void bar(void);
Index: clang/test/Parser/cxx11-stmt-attributes.cpp
===================================================================
--- clang/test/Parser/cxx11-stmt-attributes.cpp
+++ clang/test/Parser/cxx11-stmt-attributes.cpp
@@ -25,7 +25,7 @@
}
[[unknown_attribute]] return; // expected-warning {{unknown attribute 'unknown_attribute' ignored}}
-
+
alignas(8) ; // expected-error {{'alignas' attribute cannot be applied to a statement}}
[[noreturn]] { } // expected-error {{'noreturn' attribute cannot be applied to a statement}}
@@ -42,7 +42,7 @@
[[unused]] switch (i) { // expected-warning {{unknown attribute 'unused' ignored}}
[[uuid]] case 0: // expected-warning {{unknown attribute 'uuid' ignored}}
[[visibility]] default: // expected-warning {{unknown attribute 'visibility' ignored}}
- [[carries_dependency]] break; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] break; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
}
[[fastcall]] goto there; // expected-warning {{unknown attribute 'fastcall' ignored}}
@@ -54,28 +54,28 @@
[[weakref]] return; // expected-warning {{unknown attribute 'weakref' ignored}}
- [[carries_dependency]] ; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- [[carries_dependency]] { } // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- [[carries_dependency]] if (0) { } // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- [[carries_dependency]] for (;;); // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- [[carries_dependency]] do { // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- [[carries_dependency]] continue; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}} ignored}}
+ [[gnu::nonnull]] ; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] { } // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] if (0) { } // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] for (;;); // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] do { // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] continue; // expected-error {{'nonnull' attribute cannot be applied to a statement}} ignored}}
} while (0);
- [[carries_dependency]] while (0); // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] while (0); // expected-error {{'nonnull' attribute cannot be applied to a statement}}
- [[carries_dependency]] switch (i) { // expected-error {{'carries_dependency' attribute cannot be applied to a statement}} ignored}}
- [[carries_dependency]] case 0: // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- [[carries_dependency]] default: // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
- [[carries_dependency]] break; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] switch (i) { // expected-error {{'nonnull' attribute cannot be applied to a statement}} ignored}}
+ [[gnu::nonnull]] case 0: // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] default: // expected-error {{'nonnull' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] break; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
}
- [[carries_dependency]] goto here; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] goto here; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
- [[carries_dependency]] try { // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] try { // expected-error {{'nonnull' attribute cannot be applied to a statement}}
} catch (...) {
}
- [[carries_dependency]] return; // expected-error {{'carries_dependency' attribute cannot be applied to a statement}}
+ [[gnu::nonnull]] return; // expected-error {{'nonnull' attribute cannot be applied to a statement}}
{
[[ ]] // expected-error {{an attribute list cannot appear here}}
Index: clang/test/Parser/cxx0x-attributes.cpp
===================================================================
--- clang/test/Parser/cxx0x-attributes.cpp
+++ clang/test/Parser/cxx0x-attributes.cpp
@@ -330,7 +330,7 @@
expected-error {{an attribute list cannot appear here}}
typedef [[gnu::used]] unsigned long [[gnu::unused]] v2; // expected-error {{'unused' attribute cannot be applied to types}} \
expected-error {{an attribute list cannot appear here}}
-int [[carries_dependency]] foo(int [[carries_dependency]] x); // expected-error 2{{'carries_dependency' attribute cannot be applied to types}}
+int [[carries_dependency]] foo(int [[carries_dependency]] x); // expected-warning 2{{unknown attribute 'carries_dependency' ignored}}
// Forbid [[gnu::...]] attributes on declarator chunks.
int *[[gnu::unused]] v3; // expected-warning {{attribute 'unused' ignored}}
@@ -339,7 +339,7 @@
[[attribute_declaration]]; // expected-warning {{unknown attribute 'attribute_declaration' ignored}}
[[noreturn]]; // expected-error {{'noreturn' attribute only applies to functions}}
-[[carries_dependency]]; // expected-error {{'carries_dependency' attribute only applies to parameters, Objective-C methods, and functions}}
+[[carries_dependency]]; // expected-warning {{unknown attribute 'carries_dependency' ignored}}
class A {
A([[gnu::unused]] int a);
Index: clang/test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -44,7 +44,6 @@
// CHECK-NEXT: Callback (SubjectMatchRule_function)
// CHECK-NEXT: CalledOnce (SubjectMatchRule_variable_is_parameter)
// CHECK-NEXT: Capability (SubjectMatchRule_record, SubjectMatchRule_type_alias)
-// CHECK-NEXT: CarriesDependency (SubjectMatchRule_variable_is_parameter, SubjectMatchRule_objc_method, SubjectMatchRule_function)
// CHECK-NEXT: Cleanup (SubjectMatchRule_variable_is_local)
// CHECK-NEXT: CmseNSEntry (SubjectMatchRule_function)
// CHECK-NEXT: Cold (SubjectMatchRule_function)
Index: clang/test/CodeCompletion/attr.cpp
===================================================================
--- clang/test/CodeCompletion/attr.cpp
+++ clang/test/CodeCompletion/attr.cpp
@@ -1,12 +1,10 @@
int a [[gnu::used]];
// RUN: %clang_cc1 -code-completion-at=%s:%(line-1):9 %s | FileCheck --check-prefix=STD %s
-// STD: COMPLETION: Pattern : __carries_dependency__
// STD-NOT: COMPLETION: Pattern : __convergent__
// STD: COMPLETION: Pattern : __gnu__::__used__
// STD-NOT: COMPLETION: Pattern : __gnu__::used
// STD-NOT: COMPLETION: Pattern : __used__
// STD: COMPLETION: Pattern : _Clang::__convergent__
-// STD: COMPLETION: Pattern : carries_dependency
// STD-NOT: COMPLETION: Pattern : clang::called_once
// STD: COMPLETION: Pattern : clang::convergent
// STD-NOT: COMPLETION: Pattern : convergent
@@ -15,11 +13,10 @@
// STD: COMPLETION: Pattern : gnu::alias(<#Aliasee#>)
// STD: COMPLETION: Pattern : gnu::used
// STD-NOT: COMPLETION: Pattern : used
-// RUN: %clang_cc1 -code-completion-at=%s:%(line-17):9 -xobjective-c++ %s | FileCheck --check-prefix=STD-OBJC %s
+// RUN: %clang_cc1 -code-completion-at=%s:%(line-15):9 -xobjective-c++ %s | FileCheck --check-prefix=STD-OBJC %s
// STD-OBJC: COMPLETION: Pattern : clang::called_once
-// RUN: %clang_cc1 -code-completion-at=%s:%(line-19):14 %s | FileCheck --check-prefix=STD-NS %s
+// RUN: %clang_cc1 -code-completion-at=%s:%(line-17):14 %s | FileCheck --check-prefix=STD-NS %s
// STD-NS-NOT: COMPLETION: Pattern : __used__
-// STD-NS-NOT: COMPLETION: Pattern : carries_dependency
// STD-NS-NOT: COMPLETION: Pattern : clang::convergent
// STD-NS-NOT: COMPLETION: Pattern : convergent
// STD-NS-NOT: COMPLETION: Pattern : gnu::used
@@ -33,7 +30,6 @@
// RUN: %clang_cc1 -code-completion-at=%s:%(line-1):15 %s | FileCheck --check-prefix=STD-USING %s
// STD-USING: COMPLETION: __gnu__
// STD-USING: COMPLETION: _Clang
-// STD-USING-NOT: COMPLETION: Pattern : carries_dependency
// STD-USING: COMPLETION: clang
// STD-USING-NOT: COMPLETION: Pattern : clang::
// STD-USING-NOT: COMPLETION: Pattern : gnu::
@@ -42,12 +38,10 @@
int d __attribute__((used));
// RUN: %clang_cc1 -code-completion-at=%s:%(line-1):22 %s | FileCheck --check-prefix=GNU %s
-// GNU: COMPLETION: Pattern : __carries_dependency__
// GNU: COMPLETION: Pattern : __convergent__
// GNU-NOT: COMPLETION: Pattern : __gnu__::__used__
// GNU: COMPLETION: Pattern : __used__
// GNU-NOT: COMPLETION: Pattern : _Clang::__convergent__
-// GNU: COMPLETION: Pattern : carries_dependency
// GNU-NOT: COMPLETION: Pattern : clang::convergent
// GNU: COMPLETION: Pattern : convergent
// GNU-NOT: COMPLETION: Pattern : gnu::used
Index: clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p2.cpp
===================================================================
--- clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p2.cpp
+++ /dev/null
@@ -1,14 +0,0 @@
-// RUN: %clang_cc1 -verify -std=c++11 %s
-
-int f(int); // expected-note 2{{declaration missing '[[carries_dependency]]' attribute is here}}
-[[carries_dependency]] int f(int); // expected-error {{function declared '[[carries_dependency]]' after its first declaration}}
-int f(int n [[carries_dependency]]); // expected-error {{parameter declared '[[carries_dependency]]' after its first declaration}}
-
-int g([[carries_dependency]] int n); // expected-note {{declaration missing '[[carries_dependency]]' attribute is here}}
-int g(int);
-[[carries_dependency]] int g(int); // expected-error {{function declared '[[carries_dependency]]' after its first declaration}}
-int g(int n [[carries_dependency]]);
-
-int h [[carries_dependency]]();
-int h();
-[[carries_dependency]] int h();
Index: clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p1.cpp
===================================================================
--- clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p1.cpp
+++ clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.depend/p1.cpp
@@ -1,32 +1,9 @@
// RUN: %clang_cc1 -verify -std=c++11 %s
+// expected-no-diagnostics
-[[carries_dependency, carries_dependency]] int m1(); // ok
-[[carries_dependency]] [[carries_dependency]] int m2(); // ok
-[[carries_dependency()]] int m3(); // expected-error {{attribute 'carries_dependency' cannot have an argument list}}
-
-[[carries_dependency]] void f1(); // FIXME: warn here
-[[carries_dependency]] int f2(); // ok
-int f3(int param [[carries_dependency]]); // ok
-[[carries_dependency]] int (*f4)(); // expected-error {{'carries_dependency' attribute only applies to parameters, Objective-C methods, and functions}}
-int (*f5 [[carries_dependency]])(); // expected-error {{'carries_dependency' attribute only applies to}}
-int (*f6)() [[carries_dependency]]; // expected-error {{'carries_dependency' attribute cannot be applied to types}}
-int (*f7)(int n [[carries_dependency]]); // expected-error {{'[[carries_dependency]]' attribute only allowed on parameter in a function declaration}}
-int (((f8)))(int n [[carries_dependency]]); // ok
-int (*f9(int n))(int n [[carries_dependency]]); // expected-error {{'[[carries_dependency]]' attribute only allowed on parameter in a function declaration}}
-int typedef f10(int n [[carries_dependency]]); // expected-error {{'[[carries_dependency]]' attribute only allowed on parameter in a function declaration}}
-using T = int(int n [[carries_dependency]]); // expected-error {{'[[carries_dependency]]' attribute only allowed on parameter in a function declaration}}
-struct S {
- [[carries_dependency]] int f(int n [[carries_dependency]]); // ok
- int (*p)(int n [[carries_dependency]]); // expected-error {{'[[carries_dependency]]' attribute only allowed on parameter in a function declaration}}
-};
-void f() {
- [[carries_dependency]] int f(int n [[carries_dependency]]); // ok
- [[carries_dependency]] // expected-error {{'carries_dependency' attribute only applies to}}
- int (*p)(int n [[carries_dependency]]); // expected-error {{'[[carries_dependency]]' attribute only allowed on parameter in a function declaration}}
-}
-
-auto l1 = [](int n [[carries_dependency]]) {};
-// There's no way to write a lambda such that the return value carries
-// a dependency, because an attribute applied to the lambda appertains to
-// the *type* of the operator() function, not to the function itself.
-auto l2 = []() [[carries_dependency]] {}; // expected-error {{'carries_dependency' attribute cannot be applied to types}}
+// We do not do anything with [[carries_dependency]], so we do not
+// claim to support it. We ignore it as we would any other unknown
+// attribute.
+#if __has_cpp_attribute(carries_dependency)
+#error "Did not expect to support carries_dependency"
+#endif
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -2301,21 +2301,6 @@
D->addAttr(::new (S.Context) VecReturnAttr(S.Context, AL));
}
-static void handleDependencyAttr(Sema &S, Scope *Scope, Decl *D,
- const ParsedAttr &AL) {
- if (isa<ParmVarDecl>(D)) {
- // [[carries_dependency]] can only be applied to a parameter if it is a
- // parameter of a function declaration or lambda.
- if (!(Scope->getFlags() & clang::Scope::FunctionDeclarationScope)) {
- S.Diag(AL.getLoc(),
- diag::err_carries_dependency_param_not_function_decl);
- return;
- }
- }
-
- D->addAttr(::new (S.Context) CarriesDependencyAttr(S.Context, AL));
-}
-
static void handleUnusedAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
bool IsCXX17Attr = AL.isCXX11Attribute() && !AL.getScopeName();
@@ -8775,9 +8760,6 @@
case ParsedAttr::AT_Availability:
handleAvailabilityAttr(S, D, AL);
break;
- case ParsedAttr::AT_CarriesDependency:
- handleDependencyAttr(S, scope, D, AL);
- break;
case ParsedAttr::AT_CPUDispatch:
case ParsedAttr::AT_CPUSpecific:
handleCPUSpecificAttr(S, D, AL);
Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -3317,24 +3317,6 @@
static void mergeParamDeclAttributes(ParmVarDecl *newDecl,
const ParmVarDecl *oldDecl,
Sema &S) {
- // C++11 [dcl.attr.depend]p2:
- // The first declaration of a function shall specify the
- // carries_dependency attribute for its declarator-id if any declaration
- // of the function specifies the carries_dependency attribute.
- const CarriesDependencyAttr *CDA = newDecl->getAttr<CarriesDependencyAttr>();
- if (CDA && !oldDecl->hasAttr<CarriesDependencyAttr>()) {
- S.Diag(CDA->getLocation(),
- diag::err_carries_dependency_missing_on_first_decl) << 1/*Param*/;
- // Find the first declaration of the parameter.
- // FIXME: Should we build redeclaration chains for function parameters?
- const FunctionDecl *FirstFD =
- cast<FunctionDecl>(oldDecl->getDeclContext())->getFirstDecl();
- const ParmVarDecl *FirstVD =
- FirstFD->getParamDecl(oldDecl->getFunctionScopeIndex());
- S.Diag(FirstVD->getLocation(),
- diag::note_carries_dependency_missing_first_decl) << 1/*Param*/;
- }
-
if (!oldDecl->hasAttrs())
return;
@@ -4031,18 +4013,6 @@
Diag(Old->getLocation(), diag::note_previous_declaration);
}
- // C++11 [dcl.attr.depend]p2:
- // The first declaration of a function shall specify the
- // carries_dependency attribute for its declarator-id if any declaration
- // of the function specifies the carries_dependency attribute.
- const CarriesDependencyAttr *CDA = New->getAttr<CarriesDependencyAttr>();
- if (CDA && !Old->hasAttr<CarriesDependencyAttr>()) {
- Diag(CDA->getLocation(),
- diag::err_carries_dependency_missing_on_first_decl) << 0/*Function*/;
- Diag(Old->getFirstDecl()->getLocation(),
- diag::note_carries_dependency_missing_first_decl) << 0/*Function*/;
- }
-
// (C++98 8.3.5p3):
// All declarations for a function shall agree exactly in both the
// return type and the parameter-type-list.
Index: clang/lib/Parse/ParseDeclCXX.cpp
===================================================================
--- clang/lib/Parse/ParseDeclCXX.cpp
+++ clang/lib/Parse/ParseDeclCXX.cpp
@@ -4320,7 +4320,6 @@
IdentifierInfo *ScopeName) {
switch (
ParsedAttr::getParsedKind(AttrName, ScopeName, ParsedAttr::AS_CXX11)) {
- case ParsedAttr::AT_CarriesDependency:
case ParsedAttr::AT_Deprecated:
case ParsedAttr::AT_FallThrough:
case ParsedAttr::AT_CXX11NoReturn:
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -283,23 +283,6 @@
}];
}
-def CarriesDependencyDocs : Documentation {
- let Category = DocCatFunction;
- let Content = [{
-The ``carries_dependency`` attribute specifies dependency propagation into and
-out of functions.
-
-When specified on a function or Objective-C method, the ``carries_dependency``
-attribute means that the return value carries a dependency out of the function,
-so that the implementation need not constrain ordering upon return from that
-function. Implementations of the function and its caller may choose to preserve
-dependencies instead of emitting memory ordering instructions such as fences.
-
-Note, this attribute does not change the meaning of the program, but may result
-in generation of more efficient code.
- }];
-}
-
def CPUSpecificCPUDispatchDocs : Documentation {
let Category = DocCatFunction;
let Content = [{
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -978,13 +978,6 @@
let Spellings = [GNU<"bounded">];
}
-def CarriesDependency : InheritableParamAttr {
- let Spellings = [GNU<"carries_dependency">,
- CXX11<"","carries_dependency", 200809>];
- let Subjects = SubjectList<[ParmVar, ObjCMethod, Function], ErrorDiag>;
- let Documentation = [CarriesDependencyDocs];
-}
-
def CDecl : DeclOrTypeAttr {
let Spellings = [GCC<"cdecl">, Keyword<"__cdecl">, Keyword<"_cdecl">];
// let Subjects = [Function, ObjCMethod];
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -127,6 +127,13 @@
``std::move, std::forward`` et al. it is now treated as a compiler builtin and implemented
directly rather than instantiating the definition from the standard library.
+- Clang no longer claims to support the ``[[carries_dependency]]`` attribute.
+ We have not implemented any semantics for this attribute in the past decade,
+ have no plans to implement any in the future, and so returning nonzero from
+ ``__has_cpp_attribute`` was a disservice. The attribute is now treated as an
+ unknown attribute and ``__has_cpp_attribute(carries_dependency)`` now returns
+ zero.
+
C++20 Feature Support
^^^^^^^^^^^^^^^^^^^^^
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