clang/test/CodeGenCXX/msabi-ctor-abstract-vbase.cpp

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