| 1 | // RUN: %clang_cc1 -triple x86_64-windows-msvc %s -emit-llvm -fexceptions -o - | FileCheck %s |
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| 2 | |
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| 3 | // PR41065: As background, when constructing a complete object, virtual bases |
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| 4 | // are constructed first. If an exception is thrown while constructing a |
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| 5 | // subobject later, those virtual bases are destroyed, so sema references the |
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| 6 | // relevant constructors and destructors of every base class in case they are |
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| 7 | // needed. |
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| 8 | // |
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| 9 | // However, an abstract class can never be used to construct a complete object. |
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| 10 | // In the Itanium C++ ABI, this works out nicely, because we never end up |
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| 11 | // emitting the "complete" constructor variant, only the "base" constructor |
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| 12 | // variant, which can be called by constructors of derived classes. For various |
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| 13 | // reasons, Sema does not mark ctors and dtors of virtual bases referenced when |
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| 14 | // the constructor of an abstract class is emitted. |
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| 15 | // |
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| 16 | // In the Microsoft ABI, there are no complete/base variants, so before PR41065 |
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| 17 | // was fixed, the constructor of an abstract class could reference special |
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| 18 | // members of a virtual base without marking them referenced. This could lead to |
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| 19 | // unresolved symbol errors at link time. |
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| 20 | // |
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| 21 | // The fix is to implement the same optimization as Sema: If the class is |
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| 22 | // abstract, don't bother initializing its virtual bases. The "is this class the |
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| 23 | // most derived class" check in the constructor will never pass, and the virtual |
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| 24 | // base constructor calls are always dead. Skip them. |
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| 25 | |
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| 26 | struct A { |
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| 27 | A(); |
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| 28 | virtual void f() = 0; |
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| 29 | virtual ~A(); |
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| 30 | }; |
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| 31 | |
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| 32 | // B has an implicit inline dtor, but is still abstract. |
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| 33 | struct B : A { |
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| 34 | B(int n); |
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| 35 | int n; |
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| 36 | }; |
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| 37 | |
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| 38 | // Still abstract |
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| 39 | struct C : virtual B { |
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| 40 | C(int n); |
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| 41 | //void f() override; |
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| 42 | }; |
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| 43 | |
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| 44 | // Not abstract, D::D calls C::C and B::B. |
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| 45 | struct D : C { |
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| 46 | D(int n); |
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| 47 | void f() override; |
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| 48 | }; |
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| 49 | |
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| 50 | void may_throw(); |
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| 51 | C::C(int n) : B(n) { may_throw(); } |
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| 52 | |
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| 53 | // No branches, no constructor calls before may_throw(); |
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| 54 | // |
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| 55 | // 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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| 56 | // CHECK-NOT: br i1 |
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| 57 | // CHECK-NOT: {{call.*@"\?0}} |
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| 58 | // CHECK: call void @"?may_throw@@YAXXZ"() |
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| 59 | // no cleanups |
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| 60 | |
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| 61 | |
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| 62 | D::D(int n) : C(n), B(n) { may_throw(); } |
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| 63 | |
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| 64 | // Conditionally construct (and destroy) vbase B, unconditionally C. |
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| 65 | // |
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| 66 | // 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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| 67 | // CHECK: icmp ne i32 {{.*}}, 0 |
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| 68 | // CHECK: br i1 |
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| 69 | // CHECK: call %struct.B* @"??0B@@QEAA@H@Z" |
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| 70 | // CHECK: br label |
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| 71 | // CHECK: invoke %struct.C* @"??0C@@QEAA@H@Z" |
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| 72 | // CHECK: invoke void @"?may_throw@@YAXXZ"() |
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| 73 | // CHECK: cleanuppad |
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| 74 | // CHECK: call void @"??1C@@UEAA@XZ" |
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| 75 | // CHECK: cleanupret |
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| 76 | // |
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| 77 | // CHECK: cleanuppad |
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| 78 | // CHECK: icmp ne i32 {{.*}}, 0 |
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| 79 | // CHECK: br i1 |
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| 80 | // CHECK: call void @"??1B@@UEAA@XZ" |
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| 81 | // CHECK: br label |
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| 82 | // CHECK: cleanupret |
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| 83 | |
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