[Clang][Interp] Assert on virtual func call from array elem

Fixes #152893.

An assert was raised when a constexpr virtual function was called from
an constexpr array element with -fexperimental-new-constant-interpreter
set.

Author: mariusdr

clang/lib/AST/ByteCode/Interp.cpp

@@ -1666,10 +1666,15 @@ bool CallVirt(InterpState &S, CodePtr OpPC, const Function *Func,
       TypePtr = TypePtr.getBase();
 
     QualType DynamicType = TypePtr.getType();
-    if (DynamicType->isPointerType() || DynamicType->isReferenceType())
+    if (DynamicType->isPointerType() || DynamicType->isReferenceType()) {
       DynamicDecl = DynamicType->getPointeeCXXRecordDecl();
-    else
+    } else if (DynamicType->isArrayType()) {
+      const Type *ElemType = DynamicType->getPointeeOrArrayElementType();
+      assert(ElemType);
+      DynamicDecl = ElemType->getAsCXXRecordDecl();
+    } else {
       DynamicDecl = DynamicType->getAsCXXRecordDecl();
+    }
   }
   assert(DynamicDecl);
 

clang/test/AST/ByteCode/cxx20.cpp

@@ -1100,3 +1100,25 @@ namespace DiscardedTrivialCXXConstructExpr {
   constexpr int y = foo(12); // both-error {{must be initialized by a constant expression}} \
                              // both-note {{in call to}}
 }
+
+namespace VirtualFunctionCallThroughArrayElem {
+  struct X {
+    constexpr virtual int foo() const {
+      return 3;
+    }
+  };
+  constexpr X xs[5];
+  static_assert(xs[3].foo() == 3);
+
+  constexpr X xs2[1][2];
+  static_assert(xs2[0].foo() == 3); // both-error {{is not a structure or union}}
+  static_assert(xs2[0][0].foo() == 3);
+
+  struct Y: public X {
+    constexpr int foo() const override {
+      return 1;
+    }
+  };
+  constexpr Y ys[20];
+  static_assert(ys[12].foo() == static_cast<const X&>(ys[12]).foo());
+}