[MS ABI] Correctly make paths through covariant virtual bases

There can be multiple virtual bases which are on the path to a vfptr
when one vbase virtually inherits from another.  We should prefer the
most derived virtual base which covariantly overrides a method in the
vfptr class;  if we do not lengthen the path this way, we will end up
with too few vftable entries.

This fixes PR21073.

llvm-svn: 236239

2 files changed, 28 insertions, 1 deletions

diff --git a/clang/test/CodeGenCXX/microsoft-abi-vtables-return-thunks.cpp b/clang/test/CodeGenCXX/microsoft-abi-vtables-return-thunks.cpp
index 072cb956035..36c6434d549 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-vtables-return-thunks.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-vtables-return-thunks.cpp
@@ -128,3 +128,30 @@ C::C() {}
 // GLOBALS: @"\01?f@B@pr20479@@QAEPAUA@2@XZ"
 // GLOBALS: @"\01?f@B@pr20479@@UAEPAU12@XZ"
 }
+
+namespace pr21073 {
+struct A {
+  virtual A *f();
+};
+
+struct B : virtual A {
+  virtual B *f();
+};
+
+struct C : virtual A, virtual B {
+// VFTABLES-LABEL: VFTable for 'pr21073::A' in 'pr21073::B' in 'pr21073::C' (2 entries).
+// VFTABLES-NEXT:   0 | pr21073::B *pr21073::B::f()
+// VFTABLES-NEXT:       [return adjustment (to type 'struct pr21073::A *'): vbase #1, 0 non-virtual]
+// VFTABLES-NEXT:       [this adjustment: 8 non-virtual]
+// VFTABLES-NEXT:   1 | pr21073::B *pr21073::B::f()
+// VFTABLES-NEXT:       [return adjustment (to type 'struct pr21073::B *'): 0 non-virtual]
+// VFTABLES-NEXT:       [this adjustment: 8 non-virtual]
+  C();
+};
+
+C::C() {}
+
+// GLOBALS-LABEL: @"\01??_7C@pr21073@@6B@" = linkonce_odr unnamed_addr constant [2 x i8*]
+// GLOBALS: @"\01?f@B@pr21073@@WPPPPPPPI@AEPAUA@2@XZ"
+// GLOBALS: @"\01?f@B@pr21073@@WPPPPPPPI@AEPAU12@XZ"
+}
diff --git a/clang/test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance.cpp b/clang/test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance.cpp
index 83f8114bae9..d600ebbf4c2 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance.cpp
@@ -423,7 +423,7 @@ void use(T *obj) { obj->f(); }
 
 namespace Test10 {
 struct X : virtual C, virtual A {
-  // CHECK-LABEL: VFTable for 'A' in 'C' in 'Test10::X' (2 entries).
+  // CHECK-LABEL: VFTable for 'A' in 'Test10::X' (2 entries).
   // CHECK-NEXT: 0 | void Test10::X::f()
   // CHECK-NEXT: 1 | void A::z()