[runtime] [proxy] Implementing [[Call]]

src/x64/builtins-x64.cc

Index: src/x64/builtins-x64.cc
diff --git a/src/x64/builtins-x64.cc b/src/x64/builtins-x64.cc
index 1a6ee7cda1e836d9b9a5fe465f9edb43080bd339..31237d8131f0728aff3c454dd05798004ec8969f 100644
--- a/src/x64/builtins-x64.cc
+++ b/src/x64/builtins-x64.cc
@@ -1745,8 +1745,16 @@ void Builtins::Generate_Call(MacroAssembler* masm, ConvertReceiverMode mode) {
   __ CmpInstanceType(rcx, JS_PROXY_TYPE);
   __ j(not_equal, &non_function);
 
-  // 1. Call to function proxy.
-  // TODO(neis): Implement [[Call]] on proxies.
+  // 1. Runtime fallback for Proxy [[Call]].
+  __ PopReturnAddressTo(kScratchRegister);
+  __ Push(rdi);
+  __ PushReturnAddressFrom(kScratchRegister);
+  // Increase the arguments size to include the pushed function and the
+  // existing receiver on the stack.
+  __ addp(rax, Immediate(2));
+  // Tail-call to the runtime.
+  __ JumpToExternalReference(
+      ExternalReference(Runtime::kJSProxyCall, masm->isolate()), 1);
 
   // 2. Call to something else, which might have a [[Call]] internal method (if
   // not we raise an exception).