rnk created this revision.
Clang typically warns that in the following class hierarchy, 'A' is
inaccessible because there is no series of casts that the user can
write to access it unambiguously:
struct A { };
struct B : A { };
struct C : A, B { };
MSVC allows the user to convert from C* to A*, though, and we've
encountered this issue in the latest Windows SDK headers.
This patch allows this conversion when -fms-compatibility is set and
adds a warning for it under -Wmicrosoft-inaccessible-base.
https://reviews.llvm.org/D39389
Files:
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaDeclCXX.cpp
clang/test/CodeGenCXX/microsoft-inaccessible-base.cpp
clang/test/SemaCXX/accessible-base.cpp
Index: clang/test/SemaCXX/accessible-base.cpp
===================================================================
--- clang/test/SemaCXX/accessible-base.cpp
+++ clang/test/SemaCXX/accessible-base.cpp
@@ -1,23 +1,51 @@
// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -DMS -fms-compatibility -Wmicrosoft-inaccessible-base -fsyntax-only -verify %s
struct A {
int a;
};
-struct X1 : virtual A
+struct X1 : virtual A
{};
struct Y1 : X1, virtual A
{};
struct Y2 : X1, A // expected-warning{{direct base 'A' is inaccessible due to ambiguity:\n struct Y2 -> struct X1 -> struct A\n struct Y2 -> struct A}}
{};
-struct X2 : A
+struct X2 : A
{};
struct Z1 : X2, virtual A // expected-warning{{direct base 'A' is inaccessible due to ambiguity:\n struct Z1 -> struct X2 -> struct A\n struct Z1 -> struct A}}
{};
struct Z2 : X2, A // expected-warning{{direct base 'A' is inaccessible due to ambiguity:\n struct Z2 -> struct X2 -> struct A\n struct Z2 -> struct A}}
{};
+
+A *y2_to_a(Y2 *p) {
+#ifdef MS
+ // expected-warning@+4 {{accessing inaccessible direct base 'A' of 'Y2' is a Microsoft extension}}
+#else
+ // expected-error@+2 {{ambiguous conversion}}
+#endif
+ return p;
+}
+
+A *z1_to_a(Z1 *p) {
+#ifdef MS
+ // expected-warning@+4 {{accessing inaccessible direct base 'A' of 'Z1' is a Microsoft extension}}
+#else
+ // expected-error@+2 {{ambiguous conversion}}
+#endif
+ return p;
+}
+
+A *z1_to_a(Z2 *p) {
+#ifdef MS
+ // expected-warning@+4 {{accessing inaccessible direct base 'A' of 'Z2' is a Microsoft extension}}
+#else
+ // expected-error@+2 {{ambiguous conversion}}
+#endif
+ return p;
+}
Index: clang/test/CodeGenCXX/microsoft-inaccessible-base.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/microsoft-inaccessible-base.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -fms-compatibility -triple x86_64-windows-msvc %s -emit-llvm -o - | FileCheck %s
+
+// Make sure we choose the *direct* base path when doing these conversions.
+
+// CHECK: %struct.C = type { %struct.A, %struct.B }
+// CHECK: %struct.D = type { %struct.B, %struct.A }
+
+struct A { int a; };
+struct B : A { int b; };
+
+struct C : A, B { };
+extern "C" A *a_from_c(C *p) { return p; }
+// CHECK-LABEL: define %struct.A* @a_from_c(%struct.C* %{{.*}})
+// CHECK: bitcast %struct.C* %{{.*}} to %struct.A*
+
+struct D : B, A { };
+extern "C" A *a_from_d(D *p) { return p; }
+// CHECK-LABEL: define %struct.A* @a_from_d(%struct.D* %{{.*}})
+// CHECK: %[[p_i8:[^ ]*]] = bitcast %struct.D* %{{.*}} to i8*
+// CHECK: getelementptr inbounds i8, i8* %[[p_i8]], i64 8
Index: clang/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- clang/lib/Sema/SemaDeclCXX.cpp
+++ clang/lib/Sema/SemaDeclCXX.cpp
@@ -2503,13 +2503,8 @@
return DerivedRD->isDerivedFrom(BaseRD, Paths);
}
-void Sema::BuildBasePathArray(const CXXBasePaths &Paths,
- CXXCastPath &BasePathArray) {
- assert(BasePathArray.empty() && "Base path array must be empty!");
- assert(Paths.isRecordingPaths() && "Must record paths!");
-
- const CXXBasePath &Path = Paths.front();
-
+static void BuildBasePathArray(const CXXBasePath &Path,
+ CXXCastPath &BasePathArray) {
// We first go backward and check if we have a virtual base.
// FIXME: It would be better if CXXBasePath had the base specifier for
// the nearest virtual base.
@@ -2526,6 +2521,13 @@
BasePathArray.push_back(const_cast<CXXBaseSpecifier*>(Path[I].Base));
}
+
+void Sema::BuildBasePathArray(const CXXBasePaths &Paths,
+ CXXCastPath &BasePathArray) {
+ assert(BasePathArray.empty() && "Base path array must be empty!");
+ assert(Paths.isRecordingPaths() && "Must record paths!");
+ return ::BuildBasePathArray(Paths.front(), BasePathArray);
+}
/// CheckDerivedToBaseConversion - Check whether the Derived-to-Base
/// conversion (where Derived and Base are class types) is
/// well-formed, meaning that the conversion is unambiguous (and
@@ -2557,23 +2559,42 @@
"Can only be used with a derived-to-base conversion");
(void)DerivationOkay;
- if (!Paths.isAmbiguous(Context.getCanonicalType(Base).getUnqualifiedType())) {
+ const CXXBasePath *Path = nullptr;
+ if (!Paths.isAmbiguous(Context.getCanonicalType(Base).getUnqualifiedType()))
+ Path = &Paths.front();
+
+ // For MSVC compatibility, check if Derived directly inherits from Base. Clang
+ // warns about this hierarchy under -Winaccessible-base, but MSVC allows the
+ // user to access such bases.
+ if (!Path && getLangOpts().MSVCCompat) {
+ for (const CXXBasePath &PossiblePath : Paths) {
+ if (PossiblePath.size() == 1) {
+ Path = &PossiblePath;
+ if (AmbigiousBaseConvID)
+ Diag(Loc, diag::ext_ms_ambiguous_direct_base)
+ << Base << Derived << Range;
+ break;
+ }
+ }
+ }
+
+ if (Path) {
if (!IgnoreAccess) {
// Check that the base class can be accessed.
- switch (CheckBaseClassAccess(Loc, Base, Derived, Paths.front(),
- InaccessibleBaseID)) {
- case AR_inaccessible:
- return true;
- case AR_accessible:
- case AR_dependent:
- case AR_delayed:
- break;
+ switch (
+ CheckBaseClassAccess(Loc, Base, Derived, *Path, InaccessibleBaseID)) {
+ case AR_inaccessible:
+ return true;
+ case AR_accessible:
+ case AR_dependent:
+ case AR_delayed:
+ break;
}
}
// Build a base path if necessary.
if (BasePath)
- BuildBasePathArray(Paths, *BasePath);
+ ::BuildBasePathArray(*Path, *BasePath);
return false;
}
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7565,6 +7565,9 @@
def err_ambiguous_memptr_conv : Error<
"ambiguous conversion from pointer to member of %select{base|derived}0 "
"class %1 to pointer to member of %select{derived|base}0 class %2:%3">;
+def ext_ms_ambiguous_direct_base : ExtWarn<
+ "accessing inaccessible direct base %0 of %1 is a Microsoft extension">,
+ InGroup<MicrosoftInaccessibleBase>;
def err_memptr_conv_via_virtual : Error<
"conversion from pointer to member of class %0 to pointer to member "
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -890,6 +890,7 @@
def MicrosoftAnonTag : DiagGroup<"microsoft-anon-tag">;
def MicrosoftCommentPaste : DiagGroup<"microsoft-comment-paste">;
def MicrosoftEndOfFile : DiagGroup<"microsoft-end-of-file">;
+def MicrosoftInaccessibleBase : DiagGroup<"microsoft-inaccessible-base">;
// Aliases.
def : DiagGroup<"msvc-include", [MicrosoftInclude]>;
// -Wmsvc-include = -Wmicrosoft-include
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