llvm-project/clang/test/SemaCXX/warn-weak-vtables.cpp

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// RUN: %clang_cc1 %s -fsyntax-only -verify -triple %itanium_abi_triple -Wweak-vtables -Wweak-template-vtables
//
// Check that this warning is disabled on MS ABI targets which don't have key
// functions.
// RUN: %clang_cc1 %s -fsyntax-only -triple %ms_abi_triple -Werror -Wweak-vtables -Wweak-template-vtables
struct A { // expected-warning {{'A' has no out-of-line virtual method definitions; its vtable will be emitted in every translation unit}}
virtual void f() { }
};
template<typename T> struct B {
virtual void f() { }
};
namespace {
struct C {
virtual void f() { }
};
}
void f() {
struct A {
virtual void f() { }
};
Rework when and how vtables are emitted, by tracking where vtables are "used" (e.g., we will refer to the vtable in the generated code) and when they are defined (i.e., because we've seen the key function definition). Previously, we were effectively tracking "potential definitions" rather than uses, so we were a bit too eager about emitting vtables for classes without key functions. The new scheme: - For every use of a vtable, Sema calls MarkVTableUsed() to indicate the use. For example, this occurs when calling a virtual member function of the class, defining a constructor of that class type, dynamic_cast'ing from that type to a derived class, casting to/through a virtual base class, etc. - For every definition of a vtable, Sema calls MarkVTableUsed() to indicate the definition. This happens at the end of the translation unit for classes whose key function has been defined (so we can delay computation of the key function; see PR6564), and will also occur with explicit template instantiation definitions. - For every vtable defined/used, we mark all of the virtual member functions of that vtable as defined/used, unless we know that the key function is in another translation unit. This instantiates virtual member functions when needed. - At the end of the translation unit, Sema tells CodeGen (via the ASTConsumer) which vtables must be defined (CodeGen will define them) and which may be used (for which CodeGen will define the vtables lazily). From a language perspective, both the old and the new schemes are permissible: we're allowed to instantiate virtual member functions whenever we want per the standard. However, all other C++ compilers were more lazy than we were, and our eagerness was both a performance issue (we instantiated too much) and a portability problem (we broke Boost test cases, which now pass). Notes: (1) There's a ton of churn in the tests, because the order in which vtables get emitted to IR has changed. I've tried to isolate some of the larger tests from these issues. (2) Some diagnostics related to implicitly-instantiated/implicitly-defined virtual member functions have moved to the point of first use/definition. It's better this way. (3) I could use a review of the places where we MarkVTableUsed, to see if I missed any place where the language effectively requires a vtable. Fixes PR7114 and PR6564. llvm-svn: 103718
2010-05-14 00:44:06 +08:00
Don't let virtual calls and dynamic casts call Sema::MarkVTableUsed(). clang currently calls MarkVTableUsed() for classes that get their virtual methods called or that participate in a dynamic_cast. This is unnecessary, since CodeGen only emits vtables when it generates constructor, destructor, and vtt code. (*) Note that Sema::MarkVTableUsed() doesn't cause the emission of a vtable. Its main user-visible effect is that it instantiates virtual member functions of template classes, to make sure that if codegen decides to write a vtable all the entries in the vtable are defined. While this shouldn't change the behavior of codegen (other than being faster), it does make clang more permissive: virtual methods of templates (in particular destructors) end up being instantiated less often. In particular, classes that have members that are smart pointers to incomplete types will now get their implicit virtual destructor instantiated less frequently. For example, this used to not compile but does now compile: template <typename T> struct OwnPtr { ~OwnPtr() { static_assert((sizeof(T) > 0), "TypeMustBeComplete"); } }; class ScriptLoader; struct Base { virtual ~Base(); }; struct Sub : public Base { virtual void someFun() const {} OwnPtr<ScriptLoader> m_loader; }; void f(Sub *s) { s->someFun(); } The more permissive behavior matches both gcc (where this is not often observable, since in practice most things with virtual methods have a key function, and Sema::DefineUsedVTables() skips vtables for classes with key functions) and cl (which is my motivation for this change) – this fixes PR20337. See this issue and the review thread for some discussions about optimizations. This is similar to r213109 in spirit. r225761 was a prerequisite for this change. Various tests relied on "a->f()" marking a's vtable as used (in the sema sense), switch these to just construct a on the stack. This forces instantiation of the implicit constructor, which will mark the vtable as used. (*) The exception is -fapple-kext mode: In this mode, qualified calls to virtual functions (`a->Base::f()`) still go through the vtable, and since the vtable pointer off this doesn't point to Base's vtable, this needs to reference Base's vtable directly. To keep this working, keep referencing the vtable for virtual calls in apple kext mode. llvm-svn: 227073
2015-01-26 14:23:36 +08:00
A a;
Rework when and how vtables are emitted, by tracking where vtables are "used" (e.g., we will refer to the vtable in the generated code) and when they are defined (i.e., because we've seen the key function definition). Previously, we were effectively tracking "potential definitions" rather than uses, so we were a bit too eager about emitting vtables for classes without key functions. The new scheme: - For every use of a vtable, Sema calls MarkVTableUsed() to indicate the use. For example, this occurs when calling a virtual member function of the class, defining a constructor of that class type, dynamic_cast'ing from that type to a derived class, casting to/through a virtual base class, etc. - For every definition of a vtable, Sema calls MarkVTableUsed() to indicate the definition. This happens at the end of the translation unit for classes whose key function has been defined (so we can delay computation of the key function; see PR6564), and will also occur with explicit template instantiation definitions. - For every vtable defined/used, we mark all of the virtual member functions of that vtable as defined/used, unless we know that the key function is in another translation unit. This instantiates virtual member functions when needed. - At the end of the translation unit, Sema tells CodeGen (via the ASTConsumer) which vtables must be defined (CodeGen will define them) and which may be used (for which CodeGen will define the vtables lazily). From a language perspective, both the old and the new schemes are permissible: we're allowed to instantiate virtual member functions whenever we want per the standard. However, all other C++ compilers were more lazy than we were, and our eagerness was both a performance issue (we instantiated too much) and a portability problem (we broke Boost test cases, which now pass). Notes: (1) There's a ton of churn in the tests, because the order in which vtables get emitted to IR has changed. I've tried to isolate some of the larger tests from these issues. (2) Some diagnostics related to implicitly-instantiated/implicitly-defined virtual member functions have moved to the point of first use/definition. It's better this way. (3) I could use a review of the places where we MarkVTableUsed, to see if I missed any place where the language effectively requires a vtable. Fixes PR7114 and PR6564. llvm-svn: 103718
2010-05-14 00:44:06 +08:00
}
// Use the vtables
Don't let virtual calls and dynamic casts call Sema::MarkVTableUsed(). clang currently calls MarkVTableUsed() for classes that get their virtual methods called or that participate in a dynamic_cast. This is unnecessary, since CodeGen only emits vtables when it generates constructor, destructor, and vtt code. (*) Note that Sema::MarkVTableUsed() doesn't cause the emission of a vtable. Its main user-visible effect is that it instantiates virtual member functions of template classes, to make sure that if codegen decides to write a vtable all the entries in the vtable are defined. While this shouldn't change the behavior of codegen (other than being faster), it does make clang more permissive: virtual methods of templates (in particular destructors) end up being instantiated less often. In particular, classes that have members that are smart pointers to incomplete types will now get their implicit virtual destructor instantiated less frequently. For example, this used to not compile but does now compile: template <typename T> struct OwnPtr { ~OwnPtr() { static_assert((sizeof(T) > 0), "TypeMustBeComplete"); } }; class ScriptLoader; struct Base { virtual ~Base(); }; struct Sub : public Base { virtual void someFun() const {} OwnPtr<ScriptLoader> m_loader; }; void f(Sub *s) { s->someFun(); } The more permissive behavior matches both gcc (where this is not often observable, since in practice most things with virtual methods have a key function, and Sema::DefineUsedVTables() skips vtables for classes with key functions) and cl (which is my motivation for this change) – this fixes PR20337. See this issue and the review thread for some discussions about optimizations. This is similar to r213109 in spirit. r225761 was a prerequisite for this change. Various tests relied on "a->f()" marking a's vtable as used (in the sema sense), switch these to just construct a on the stack. This forces instantiation of the implicit constructor, which will mark the vtable as used. (*) The exception is -fapple-kext mode: In this mode, qualified calls to virtual functions (`a->Base::f()`) still go through the vtable, and since the vtable pointer off this doesn't point to Base's vtable, this needs to reference Base's vtable directly. To keep this working, keep referencing the vtable for virtual calls in apple kext mode. llvm-svn: 227073
2015-01-26 14:23:36 +08:00
void uses_abc() {
A a;
B<int> b;
C c;
}
// <rdar://problem/9979458>
class Parent {
public:
Parent() {}
virtual ~Parent();
virtual void * getFoo() const = 0;
};
class Derived : public Parent {
public:
Derived();
void * getFoo() const;
};
class VeryDerived : public Derived { // expected-warning{{'VeryDerived' has no out-of-line virtual method definitions; its vtable will be emitted in every translation unit}}
public:
void * getFoo() const { return 0; }
};
Parent::~Parent() {}
Don't let virtual calls and dynamic casts call Sema::MarkVTableUsed(). clang currently calls MarkVTableUsed() for classes that get their virtual methods called or that participate in a dynamic_cast. This is unnecessary, since CodeGen only emits vtables when it generates constructor, destructor, and vtt code. (*) Note that Sema::MarkVTableUsed() doesn't cause the emission of a vtable. Its main user-visible effect is that it instantiates virtual member functions of template classes, to make sure that if codegen decides to write a vtable all the entries in the vtable are defined. While this shouldn't change the behavior of codegen (other than being faster), it does make clang more permissive: virtual methods of templates (in particular destructors) end up being instantiated less often. In particular, classes that have members that are smart pointers to incomplete types will now get their implicit virtual destructor instantiated less frequently. For example, this used to not compile but does now compile: template <typename T> struct OwnPtr { ~OwnPtr() { static_assert((sizeof(T) > 0), "TypeMustBeComplete"); } }; class ScriptLoader; struct Base { virtual ~Base(); }; struct Sub : public Base { virtual void someFun() const {} OwnPtr<ScriptLoader> m_loader; }; void f(Sub *s) { s->someFun(); } The more permissive behavior matches both gcc (where this is not often observable, since in practice most things with virtual methods have a key function, and Sema::DefineUsedVTables() skips vtables for classes with key functions) and cl (which is my motivation for this change) – this fixes PR20337. See this issue and the review thread for some discussions about optimizations. This is similar to r213109 in spirit. r225761 was a prerequisite for this change. Various tests relied on "a->f()" marking a's vtable as used (in the sema sense), switch these to just construct a on the stack. This forces instantiation of the implicit constructor, which will mark the vtable as used. (*) The exception is -fapple-kext mode: In this mode, qualified calls to virtual functions (`a->Base::f()`) still go through the vtable, and since the vtable pointer off this doesn't point to Base's vtable, this needs to reference Base's vtable directly. To keep this working, keep referencing the vtable for virtual calls in apple kext mode. llvm-svn: 227073
2015-01-26 14:23:36 +08:00
void uses_derived() {
Derived d;
VeryDerived vd;
}
template<typename T> struct TemplVirt {
virtual void f();
};
template class TemplVirt<float>; // expected-warning{{explicit template instantiation 'TemplVirt<float>' will emit a vtable in every translation unit}}
template<> struct TemplVirt<bool> {
virtual void f();
};
template<> struct TemplVirt<long> { // expected-warning{{'TemplVirt<long>' has no out-of-line virtual method definitions; its vtable will be emitted in every translation unit}}
virtual void f() {}
};
Don't let virtual calls and dynamic casts call Sema::MarkVTableUsed(). clang currently calls MarkVTableUsed() for classes that get their virtual methods called or that participate in a dynamic_cast. This is unnecessary, since CodeGen only emits vtables when it generates constructor, destructor, and vtt code. (*) Note that Sema::MarkVTableUsed() doesn't cause the emission of a vtable. Its main user-visible effect is that it instantiates virtual member functions of template classes, to make sure that if codegen decides to write a vtable all the entries in the vtable are defined. While this shouldn't change the behavior of codegen (other than being faster), it does make clang more permissive: virtual methods of templates (in particular destructors) end up being instantiated less often. In particular, classes that have members that are smart pointers to incomplete types will now get their implicit virtual destructor instantiated less frequently. For example, this used to not compile but does now compile: template <typename T> struct OwnPtr { ~OwnPtr() { static_assert((sizeof(T) > 0), "TypeMustBeComplete"); } }; class ScriptLoader; struct Base { virtual ~Base(); }; struct Sub : public Base { virtual void someFun() const {} OwnPtr<ScriptLoader> m_loader; }; void f(Sub *s) { s->someFun(); } The more permissive behavior matches both gcc (where this is not often observable, since in practice most things with virtual methods have a key function, and Sema::DefineUsedVTables() skips vtables for classes with key functions) and cl (which is my motivation for this change) – this fixes PR20337. See this issue and the review thread for some discussions about optimizations. This is similar to r213109 in spirit. r225761 was a prerequisite for this change. Various tests relied on "a->f()" marking a's vtable as used (in the sema sense), switch these to just construct a on the stack. This forces instantiation of the implicit constructor, which will mark the vtable as used. (*) The exception is -fapple-kext mode: In this mode, qualified calls to virtual functions (`a->Base::f()`) still go through the vtable, and since the vtable pointer off this doesn't point to Base's vtable, this needs to reference Base's vtable directly. To keep this working, keep referencing the vtable for virtual calls in apple kext mode. llvm-svn: 227073
2015-01-26 14:23:36 +08:00
void uses_templ() {
TemplVirt<float> f;
TemplVirt<bool> b;
TemplVirt<long> l;
}