Verify that the method referenced in {Class,Super}MethodInsts appears in the class vtable.

lib/SIL/SILVerifier.cpp

@@ -33,6 +33,7 @@
 #include "swift/SIL/SILModule.h"
 #include "swift/SIL/SILOpenedArchetypesTracker.h"
 #include "swift/SIL/SILVTable.h"
+#include "swift/SIL/SILVTableVisitor.h"
 #include "swift/SIL/SILVisitor.h"
 #include "swift/SIL/BasicBlockUtils.h"
 #include "swift/SIL/TypeLowering.h"
@@ -2554,7 +2555,56 @@ public:
                                      F.getASTContext());
     return SILType::getPrimitiveObjectType(fnTy);
   }
-  
+
+  /// Visitor class that checks whether a given decl ref has an entry in the
+  /// class's vtable.
+  class VerifyClassMethodVisitor
+      : public SILVTableVisitor<VerifyClassMethodVisitor>
+  {
+  public:
+    SILDeclRef MethodToSee;
+    bool Seen = false;
+    
+    VerifyClassMethodVisitor(ClassDecl *theClass,
+                             SILDeclRef method)
+      : MethodToSee(method)
+    {
+      addVTableEntries(theClass);
+    }
+    
+    bool methodMatches(SILDeclRef method) {
+      auto methodToCheck = MethodToSee;
+      do {
+        if (method == methodToCheck) {
+          return true;
+        }
+      } while ((methodToCheck = methodToCheck.getNextOverriddenVTableEntry()));
+
+      return false;
+    }
+    
+    void addMethod(SILDeclRef method) {
+      if (Seen)
+        return;
+      if (methodMatches(method))
+        Seen = true;
+    }
+    
+    void addMethodOverride(SILDeclRef base, SILDeclRef derived) {
+      if (Seen)
+        return;
+      // The derived method should already have been checked.
+      // Test against the overridden base.
+      if (methodMatches(base))
+        Seen = true;
+    }
+
+    
+    void addPlaceholder(MissingMemberDecl *) {
+      /* no-op */
+    }
+  };
+
   void checkClassMethodInst(ClassMethodInst *CMI) {
     auto member = CMI->getMember();
     auto overrideTy = TC.getConstantOverrideType(member);
@@ -2577,6 +2627,13 @@ public:
             "foreign method cannot be dispatched natively");
     require(!isa<ExtensionDecl>(member.getDecl()->getDeclContext()),
             "extension method cannot be dispatched natively");
+    
+    // The method ought to appear in the class vtable.
+    require(VerifyClassMethodVisitor(
+                             operandType.getASTType()->getMetatypeInstanceType()
+                                       ->getClassOrBoundGenericClass(),
+                             member).Seen,
+            "method does not appear in the class's vtable");
   }
 
   void checkSuperMethodInst(SuperMethodInst *CMI) {
@@ -2607,6 +2664,13 @@ public:
 
     require(methodClass->getClassOrBoundGenericClass(),
             "super_method must look up a class method");
+
+    // The method ought to appear in the class vtable.
+    require(VerifyClassMethodVisitor(
+                             operandType.getASTType()->getMetatypeInstanceType()
+                                       ->getClassOrBoundGenericClass(),
+                             member).Seen,
+            "method does not appear in the class's vtable");    
   }
 
   void checkObjCMethodInst(ObjCMethodInst *OMI) {