83 lines
2.7 KiB
C++
83 lines
2.7 KiB
C++
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// RUN: %clang_cc1 -triple x86_64-windows-msvc %s -emit-llvm -fexceptions -o - | FileCheck %s
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// PR41065: As background, when constructing a complete object, virtual bases
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// are constructed first. If an exception is thrown while constructing a
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// subobject later, those virtual bases are destroyed, so sema references the
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// relevant constructors and destructors of every base class in case they are
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// needed.
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//
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// However, an abstract class can never be used to construct a complete object.
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// In the Itanium C++ ABI, this works out nicely, because we never end up
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// emitting the "complete" constructor variant, only the "base" constructor
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// variant, which can be called by constructors of derived classes. For various
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// reasons, Sema does not mark ctors and dtors of virtual bases referenced when
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// the constructor of an abstract class is emitted.
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//
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// In the Microsoft ABI, there are no complete/base variants, so before PR41065
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// was fixed, the constructor of an abstract class could reference special
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// members of a virtual base without marking them referenced. This could lead to
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// unresolved symbol errors at link time.
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//
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// The fix is to implement the same optimization as Sema: If the class is
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// abstract, don't bother initializing its virtual bases. The "is this class the
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// most derived class" check in the constructor will never pass, and the virtual
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// base constructor calls are always dead. Skip them.
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struct A {
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A();
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virtual void f() = 0;
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virtual ~A();
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};
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// B has an implicit inline dtor, but is still abstract.
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struct B : A {
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B(int n);
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int n;
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};
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// Still abstract
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struct C : virtual B {
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C(int n);
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//void f() override;
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};
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// Not abstract, D::D calls C::C and B::B.
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struct D : C {
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D(int n);
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void f() override;
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};
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void may_throw();
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C::C(int n) : B(n) { may_throw(); }
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// No branches, no constructor calls before may_throw();
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//
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// CHECK-LABEL: define dso_local %struct.C* @"??0C@@QEAA@H@Z"(%struct.C* {{[^,]*}} returned {{[^,]*}} %this, i32 %n, i32 %is_most_derived)
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// CHECK-NOT: br i1
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// CHECK-NOT: {{call.*@"\?0}}
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// CHECK: call void @"?may_throw@@YAXXZ"()
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// no cleanups
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D::D(int n) : C(n), B(n) { may_throw(); }
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// Conditionally construct (and destroy) vbase B, unconditionally C.
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//
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// CHECK-LABEL: define dso_local %struct.D* @"??0D@@QEAA@H@Z"(%struct.D* {{[^,]*}} returned {{[^,]*}} %this, i32 %n, i32 %is_most_derived)
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// CHECK: icmp ne i32 {{.*}}, 0
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// CHECK: br i1
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// CHECK: call %struct.B* @"??0B@@QEAA@H@Z"
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// CHECK: br label
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// CHECK: invoke %struct.C* @"??0C@@QEAA@H@Z"
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// CHECK: invoke void @"?may_throw@@YAXXZ"()
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// CHECK: cleanuppad
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// CHECK: call void @"??1C@@UEAA@XZ"
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// CHECK: cleanupret
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//
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// CHECK: cleanuppad
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// CHECK: icmp ne i32 {{.*}}, 0
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// CHECK: br i1
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// CHECK: call void @"??1B@@UEAA@XZ"
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// CHECK: br label
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// CHECK: cleanupret
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