[CIR] Fix assertion in CIRGenTypes::isFuncParamTypeConvertible (#1487)

This PR resolves an assertion failure in
`CIRGenTypes::isFuncParamTypeConvertible`, which is involved when trying
to emit a vtable entry to a virtual function whose type includes a
pointer-to-member-function.

Author: Lancern

clang/lib/CIR/CodeGen/CIRGenCXXABI.h

@@ -273,6 +273,11 @@ class CIRGenCXXABI {
   /// (in the C++ sense) with an LLVM zeroinitializer.
   virtual bool isZeroInitializable(const MemberPointerType *MPT);
 
+  /// Return whether or not a member pointers type is convertible to an IR type.
+  virtual bool isMemberPointerConvertible(const MemberPointerType *MPT) const {
+    return true;
+  }
+
   /// Gets the offsets of all the virtual base pointers in a given class.
   virtual std::vector<CharUnits> getVBPtrOffsets(const CXXRecordDecl *RD);
 

clang/lib/CIR/CodeGen/CIRGenTypes.cpp

@@ -313,7 +313,8 @@ mlir::Type CIRGenTypes::convertFunctionTypeInternal(QualType QFT) {
 bool CIRGenTypes::isFuncParamTypeConvertible(clang::QualType Ty) {
   // Some ABIs cannot have their member pointers represented in LLVM IR unless
   // certain circumstances have been reached.
-  assert(!Ty->getAs<MemberPointerType>() && "NYI");
+  if (const auto *mpt = Ty->getAs<MemberPointerType>())
+    return getCXXABI().isMemberPointerConvertible(mpt);
 
   // If this isn't a tagged type, we can convert it!
   const TagType *TT = Ty->getAs<TagType>();

clang/test/CIR/CodeGen/pointer-to-member-func.cpp

@@ -232,3 +232,11 @@ Base2MemFunc derived_to_base(DerivedMemFunc ptr) {
 // LLVM-NEXT: %[[#adj:]] = extractvalue { i64, i64 } %[[#arg]], 1
 // LLVM-NEXT: %[[#adj_adj:]] = sub i64 %[[#adj]], 16
 // LLVM-NEXT: %{{.+}} = insertvalue { i64, i64 } %[[#arg]], i64 %[[#adj_adj]], 1
+
+struct HasVTable {
+  virtual void test(void (Foo::*)());
+};
+
+// Ensure that the vfunc pointer to the function involving a pointer-to-member-
+// func could be emitted.
+void HasVTable::test(void (Foo::*)()) {}