r314037 - DR1113: anonymous namespaces formally give their contents internal linkage.
Richard Smith via cfe-commits
cfe-commits at lists.llvm.org
Fri Sep 22 16:36:18 PDT 2017
Investigating...
On 22 September 2017 at 15:58, Vitaly Buka via cfe-commits <
cfe-commits at lists.llvm.org> wrote:
> This breaks check-clang-tools
> http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_
> 64-scei-ps4-windows10pro-fast/builds/12310/steps/test/logs/stdio
>
> On Fri, Sep 22, 2017 at 3:21 PM, Richard Smith via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
>
>> Author: rsmith
>> Date: Fri Sep 22 15:21:44 2017
>> New Revision: 314037
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=314037&view=rev
>> Log:
>> DR1113: anonymous namespaces formally give their contents internal
>> linkage.
>>
>> This doesn't affect our code generation in any material way -- we already
>> give
>> such declarations internal linkage from a codegen perspective -- but it
>> has
>> some subtle effects on code validity.
>>
>> We suppress the 'L' (internal linkage) marker for mangled names in
>> anonymous
>> namespaces, because it is redundant (the information is already carried
>> by the
>> namespace); this deviates from GCC's behavior if a variable or function
>> in an
>> anonymous namespace is redundantly declared 'static' (where GCC does
>> include
>> the 'L'), but GCC's behavior is incoherent because such a declaration can
>> be
>> validly declared with or without the 'static'.
>>
>> We still deviate from the standard in one regard here: extern "C"
>> declarations
>> in anonymous namespaces are still granted external linkage. Changing
>> those does
>> not appear to have been an intentional consequence of the standard change
>> in
>> DR1113.
>>
>> Added:
>> cfe/trunk/test/CXX/drs/dr11xx.cpp
>> Modified:
>> cfe/trunk/lib/AST/Decl.cpp
>> cfe/trunk/lib/AST/ItaniumMangle.cpp
>> cfe/trunk/test/CXX/basic/basic.link/p8.cpp
>> cfe/trunk/test/CodeGenCXX/anonymous-namespaces.cpp
>> cfe/trunk/test/SemaCXX/linkage2.cpp
>> cfe/trunk/test/SemaCXX/undefined-internal.cpp
>>
>> Modified: cfe/trunk/lib/AST/Decl.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/Decl.
>> cpp?rev=314037&r1=314036&r2=314037&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/lib/AST/Decl.cpp (original)
>> +++ cfe/trunk/lib/AST/Decl.cpp Fri Sep 22 15:21:44 2017
>> @@ -619,16 +619,16 @@ LinkageComputer::getLVForNamespaceScopeD
>> if (D->isInAnonymousNamespace()) {
>> const auto *Var = dyn_cast<VarDecl>(D);
>> const auto *Func = dyn_cast<FunctionDecl>(D);
>> - // FIXME: In C++11 onwards, anonymous namespaces should give decls
>> - // within them (including those inside extern "C" contexts) internal
>> - // linkage, not unique external linkage:
>> + // FIXME: The check for extern "C" here is not justified by the
>> standard
>> + // wording, but we retain it from the pre-DR1113 model to avoid
>> breaking
>> + // code.
>> //
>> // C++11 [basic.link]p4:
>> // An unnamed namespace or a namespace declared directly or
>> indirectly
>> // within an unnamed namespace has internal linkage.
>> if ((!Var || !isFirstInExternCContext(Var)) &&
>> (!Func || !isFirstInExternCContext(Func)))
>> - return LinkageInfo::uniqueExternal();
>> + return getInternalLinkageFor(D);
>> }
>>
>> // Set up the defaults.
>> @@ -1130,7 +1130,7 @@ LinkageInfo LinkageComputer::getLVForLoc
>> if (const auto *Function = dyn_cast<FunctionDecl>(D)) {
>> if (Function->isInAnonymousNamespace() &&
>> !Function->isInExternCContext())
>> - return LinkageInfo::uniqueExternal();
>> + return getInternalLinkageFor(Function);
>>
>> // This is a "void f();" which got merged with a file static.
>> if (Function->getCanonicalDecl()->getStorageClass() == SC_Static)
>> @@ -1153,7 +1153,7 @@ LinkageInfo LinkageComputer::getLVForLoc
>> if (const auto *Var = dyn_cast<VarDecl>(D)) {
>> if (Var->hasExternalStorage()) {
>> if (Var->isInAnonymousNamespace() && !Var->isInExternCContext())
>> - return LinkageInfo::uniqueExternal();
>> + return getInternalLinkageFor(Var);
>>
>> LinkageInfo LV;
>> if (Var->getStorageClass() == SC_PrivateExtern)
>>
>> Modified: cfe/trunk/lib/AST/ItaniumMangle.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/Itaniu
>> mMangle.cpp?rev=314037&r1=314036&r2=314037&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/lib/AST/ItaniumMangle.cpp (original)
>> +++ cfe/trunk/lib/AST/ItaniumMangle.cpp Fri Sep 22 15:21:44 2017
>> @@ -1287,9 +1287,15 @@ void CXXNameMangler::mangleUnqualifiedNa
>> //
>> // void test() { extern void foo(); }
>> // static void foo();
>> + //
>> + // Don't bother with the L marker for names in anonymous
>> namespaces; the
>> + // 12_GLOBAL__N_1 mangling is quite sufficient there, and this
>> better
>> + // matches GCC anyway, because GCC does not treat anonymous
>> namespaces as
>> + // implying internal linkage.
>> if (ND && ND->getFormalLinkage() == InternalLinkage &&
>> !ND->isExternallyVisible() &&
>> - getEffectiveDeclContext(ND)->isFileContext())
>> + getEffectiveDeclContext(ND)->isFileContext() &&
>> + !ND->isInAnonymousNamespace())
>> Out << 'L';
>>
>> auto *FD = dyn_cast<FunctionDecl>(ND);
>>
>> Modified: cfe/trunk/test/CXX/basic/basic.link/p8.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/basic
>> /basic.link/p8.cpp?rev=314037&r1=314036&r2=314037&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/test/CXX/basic/basic.link/p8.cpp (original)
>> +++ cfe/trunk/test/CXX/basic/basic.link/p8.cpp Fri Sep 22 15:21:44 2017
>> @@ -52,6 +52,13 @@ void use_visible_no_linkage() {
>> visible_no_linkage3(); // expected-note {{used here}}
>> }
>>
>> +namespace {
>> + struct InternalLinkage {};
>> +}
>> +InternalLinkage internal_linkage(); // expected-error {{used but not
>> defined}}
>> +void use_internal_linkage() {
>> + internal_linkage(); // expected-note {{used here}}
>> +}
>>
>> extern inline int not_defined; // expected-error {{not defined}}
>> extern inline int defined_after_use;
>>
>> Added: cfe/trunk/test/CXX/drs/dr11xx.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/drs/
>> dr11xx.cpp?rev=314037&view=auto
>> ============================================================
>> ==================
>> --- cfe/trunk/test/CXX/drs/dr11xx.cpp (added)
>> +++ cfe/trunk/test/CXX/drs/dr11xx.cpp Fri Sep 22 15:21:44 2017
>> @@ -0,0 +1,30 @@
>> +// RUN: %clang_cc1 -std=c++98 %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>> +// RUN: %clang_cc1 -std=c++11 %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>> +// RUN: %clang_cc1 -std=c++14 %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>> +// RUN: %clang_cc1 -std=c++17 %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>> +// RUN: %clang_cc1 -std=c++2a %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>> +
>> +namespace dr1113 { // dr1113: partial
>> + namespace named {
>> + extern int a; // expected-note {{previous}}
>> + static int a; // expected-error {{static declaration of 'a' follows
>> non-static}}
>> + }
>> + namespace {
>> + extern int a;
>> + static int a; // ok, both declarations have internal linkage
>> + int b = a;
>> + }
>> +
>> + // FIXME: Per DR1113 and DR4, this is ill-formed due to ambiguity: the
>> second
>> + // 'f' has internal linkage, and so does not have C language linkage,
>> so is
>> + // not a redeclaration of the first 'f'.
>> + //
>> + // To avoid a breaking change here, Clang ignores the "internal
>> linkage" effect
>> + // of anonymous namespaces on declarations declared within an 'extern
>> "C"'
>> + // linkage-specification.
>> + extern "C" void f();
>> + namespace {
>> + extern "C" void f();
>> + }
>> + void g() { f(); }
>> +}
>>
>> Modified: cfe/trunk/test/CodeGenCXX/anonymous-namespaces.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCX
>> X/anonymous-namespaces.cpp?rev=314037&r1=314036&r2=314037&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/test/CodeGenCXX/anonymous-namespaces.cpp (original)
>> +++ cfe/trunk/test/CodeGenCXX/anonymous-namespaces.cpp Fri Sep 22
>> 15:21:44 2017
>> @@ -6,7 +6,8 @@ int f();
>>
>> namespace {
>> // CHECK-1: @_ZN12_GLOBAL__N_11bE = internal global i32 0
>> - // CHECK-1: @_ZN12_GLOBAL__N_1L1cE = internal global i32 0
>> + // CHECK-1: @_ZN12_GLOBAL__N_11cE = internal global i32 0
>> + // CHECK-1: @_ZN12_GLOBAL__N_12c2E = internal global i32 0
>> // CHECK-1: @_ZN12_GLOBAL__N_11D1dE = internal global i32 0
>> // CHECK-1: @_ZN12_GLOBAL__N_11aE = internal global i32 0
>> int a = 0;
>> @@ -15,6 +16,12 @@ namespace {
>>
>> static int c = f();
>>
>> + // Note, we can't use an 'L' mangling for c or c2 (like GCC does)
>> based on
>> + // the 'static' specifier, because the variable can be redeclared
>> without it.
>> + extern int c2;
>> + int g() { return c2; }
>> + static int c2 = f();
>> +
>> class D {
>> static int d;
>> };
>>
>> Modified: cfe/trunk/test/SemaCXX/linkage2.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/
>> linkage2.cpp?rev=314037&r1=314036&r2=314037&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/test/SemaCXX/linkage2.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/linkage2.cpp Fri Sep 22 15:21:44 2017
>> @@ -143,9 +143,10 @@ namespace test13 {
>> }
>>
>> namespace test14 {
>> + // Anonymous namespace implies internal linkage, so 'static' has no
>> effect.
>> namespace {
>> - void a(void); // expected-note {{previous declaration is here}}
>> - static void a(void) {} // expected-error {{static declaration of 'a'
>> follows non-static declaration}}
>> + void a(void);
>> + static void a(void) {}
>> }
>> }
>>
>>
>> Modified: cfe/trunk/test/SemaCXX/undefined-internal.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/
>> undefined-internal.cpp?rev=314037&r1=314036&r2=314037&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/test/SemaCXX/undefined-internal.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/undefined-internal.cpp Fri Sep 22 15:21:44
>> 2017
>> @@ -187,6 +187,10 @@ namespace OverloadUse {
>> void f();
>> void f(int); // expected-warning {{function 'OverloadUse::(anonymous
>> namespace)::f' has internal linkage but is not defined}}
>> void f(int, int); // expected-warning {{function
>> 'OverloadUse::(anonymous namespace)::f' has internal linkage but is not
>> defined}}
>> +#if __cplusplus < 201103L
>> + // expected-note at -3 {{here}}
>> + // expected-note at -3 {{here}}
>> +#endif
>> }
>> template<void x()> void t() { x(); }
>> template<void x(int)> void t(int*) { x(10); }
>> @@ -194,6 +198,10 @@ namespace OverloadUse {
>> void g(int n) {
>> t<f>(&n); // expected-note {{used here}}
>> t<f>(&n, &n); // expected-note {{used here}}
>> +#if __cplusplus < 201103L
>> + // expected-warning at -3 {{non-type template argument referring to
>> function 'f' with internal linkage}}
>> + // expected-warning at -3 {{non-type template argument referring to
>> function 'f' with internal linkage}}
>> +#endif
>> }
>> }
>>
>>
>>
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