IRGen: Use the static superclass for virtual dynamic dispatch

Following the self instance pointer to its class metadata isn't sound
for chained super calls since it means the same metadata is pulled,
resulting infinite recursion.

NFC for actual IRGen. SILGen isn't using super_method for native
dispatch yet.

rdar://problem/22749732

Author: bitjammer

lib/IRGen/GenMeta.cpp

@@ -4309,18 +4309,22 @@ llvm::Value *irgen::emitVirtualMethodValue(IRGenFunction &IGF,
 
   // Find the metadata.
   llvm::Value *metadata;
-  if ((isa<FuncDecl>(methodDecl) && cast<FuncDecl>(methodDecl)->isStatic()) ||
-      (isa<ConstructorDecl>(methodDecl) &&
-       method.kind == SILDeclRef::Kind::Allocator)) {
-    metadata = base;
-  } else {
-    metadata = emitHeapMetadataRefForHeapObject(IGF, base, baseType,
-                                                /*suppress cast*/ true);
-  }
-
   if (useSuperVTable) {
-    auto superField = emitAddressOfSuperclassRefInClassMetadata(IGF, metadata);
-    metadata = IGF.Builder.CreateLoad(superField);
+    if (auto metaTy = dyn_cast<MetatypeType>(baseType.getSwiftRValueType()))
+      baseType = SILType::getPrimitiveObjectType(metaTy.getInstanceType());
+
+    auto superType = baseType.getSuperclass(/*resolver=*/nullptr);
+    metadata = emitClassHeapMetadataRef(IGF, superType.getSwiftRValueType(),
+                                        MetadataValueType::TypeMetadata);
+  } else {
+    if ((isa<FuncDecl>(methodDecl) && cast<FuncDecl>(methodDecl)->isStatic()) ||
+        (isa<ConstructorDecl>(methodDecl) &&
+         method.kind == SILDeclRef::Kind::Allocator)) {
+      metadata = base;
+    } else {
+      metadata = emitHeapMetadataRefForHeapObject(IGF, base, baseType,
+                                                  /*suppress cast*/ true);
+    }
   }
 
   // Use the type of the method we were type-checked against, not the

test/IRGen/super_class_method.sil

@@ -49,10 +49,9 @@ sil_vtable Grandchild {
 }
 
 // CHECK-LABEL: define void @Grandchild_foo(%swift.type*) #0
-// CHECK: [[OPAQUE_GRANDCHILD:%[0-9]+]] = bitcast %swift.type* %0 to %swift.type**
-// CHECK: [[SUPER_METADATA_PTR:%[0-9]+]] = getelementptr inbounds %swift.type*, %swift.type** [[OPAQUE_GRANDCHILD]], i32 1
-// CHECK: [[SUPER_METADATA:%[0-9]+]] = load %swift.type*, %swift.type** [[SUPER_METADATA_PTR]]
-// CHECK: [[FOO_VTABLE_SLOT:%[0-9]+]] = getelementptr inbounds void (%swift.type*)*, void (%swift.type*)**
+// CHECK: [[CHILD_METADATA_PTR:%[0-9]+]] = call %swift.type* @_TMaC18super_class_method5Child()
+// CHECK: [[CASTED_CHILD_METADATA_PTR:%[0-9]+]] = bitcast %swift.type* [[CHILD_METADATA_PTR]] to void (%swift.type*)**
+// CHECK: [[FOO_VTABLE_SLOT:%[0-9]+]] = getelementptr inbounds void (%swift.type*)*, void (%swift.type*)** [[CASTED_CHILD_METADATA_PTR]]
 // CHECK: [[FOO_FNPTR:%[0-9]+]] = load void (%swift.type*)*, void (%swift.type*)** [[FOO_VTABLE_SLOT]]
 // CHECK: call void
 

test/IRGen/super_instance_method.sil

@@ -48,13 +48,10 @@ sil_vtable Grandchild {
   #Parent.foo!1: Grandchild_foo
 }
 
-// CHECK: define void @Grandchild_foo(%C21super_instance_method10Grandchild*)
-// CHECK: [[OPAQUE_GRANDCHILD:%[0-9]+]] = bitcast %C21super_instance_method10Grandchild* %0 to %swift.type**
-// CHECK: [[GRANDCHILD_METADATA:%\..*]] = load %swift.type*, %swift.type** [[OPAQUE_GRANDCHILD]]
-// CHECK: [[OPAQUE_METADATA:%[0-9]+]] = bitcast %swift.type* [[GRANDCHILD_METADATA]] to %swift.type**
-// CHECK: [[SUPER_METADATA_PTR:%[0-9]+]] = getelementptr inbounds %swift.type*, %swift.type** [[OPAQUE_METADATA]], i32 1
-// CHECK: [[SUPER_METADATA:%[0-9]+]] = load %swift.type*, %swift.type** [[SUPER_METADATA_PTR]]
-// CHECK: [[FOO_VTABLE_SLOT:%[0-9]+]] = getelementptr inbounds void (%C21super_instance_method6Parent*)*, void (%C21super_instance_method6Parent*)**
-// CHECK: [[FOO_FNPTR:%[0-9]+]] = load void (%C21super_instance_method6Parent*)*, void (%C21super_instance_method6Parent*)** [[FOO_VTABLE_SLOT]]
+// CHECK-LABEL: define void @Grandchild_foo(%C21super_instance_method10Grandchild*)
+// CHECK: [[CHILD_METADATA_PTR:%[0-9]+]] = call %swift.type* @_TMaC21super_instance_method5Child()
+// CHECK: [[CASTED_CHILD_METADATA_PTR:%[0-9]+]] = bitcast %swift.type* [[CHILD_METADATA_PTR]] to void (%C21super_instance_method6Parent*)**
+// CHECK: [[FOO_VTABLE_SLOT:%[0-9]+]] = getelementptr inbounds void (%C21super_instance_method6Parent*)*, void (%C21super_instance_method6Parent*)** [[CASTED_CHILD_METADATA_PTR]]
+// CHECK: [[FOO_FN_PTR:%[0-9]+]] = load void (%C21super_instance_method6Parent*)*, void (%C21super_instance_method6Parent*)** [[FOO_VTABLE_SLOT]]
 // CHECK: call void