Make function proxies work as constructors.

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 8976ff82d7df4cc4f8b125163cca6fb4cd42278d..530aec60f5ee753db0d289dbbcbf2261e4e60003 100644
--- a/src/x64/builtins-x64.cc
+++ b/src/x64/builtins-x64.cc
@@ -79,12 +79,12 @@ void Builtins::Generate_JSConstructCall(MacroAssembler* masm) {
   //  -- rdi: constructor function
   // -----------------------------------
 
-  Label non_function_call;
+  Label slow, non_function_call;
   // Check that function is not a smi.
   __ JumpIfSmi(rdi, &non_function_call);
   // Check that function is a JSFunction.
   __ CmpObjectType(rdi, JS_FUNCTION_TYPE, rcx);
-  __ j(not_equal, &non_function_call);
+  __ j(not_equal, &slow);
 
   // Jump to the function-specific construct stub.
   __ movq(rbx, FieldOperand(rdi, JSFunction::kSharedFunctionInfoOffset));
@@ -94,10 +94,19 @@ void Builtins::Generate_JSConstructCall(MacroAssembler* masm) {
 
   // rdi: called object
   // rax: number of arguments
+  // rcx: object map
+  Label do_call;
+  __ bind(&slow);
+  __ CmpInstanceType(rcx, JS_FUNCTION_PROXY_TYPE);
+  __ j(not_equal, &non_function_call);
+  __ GetBuiltinEntry(rdx, Builtins::CALL_FUNCTION_PROXY_AS_CONSTRUCTOR);
+  __ jmp(&do_call);
+
   __ bind(&non_function_call);
+  __ GetBuiltinEntry(rdx, Builtins::CALL_NON_FUNCTION_AS_CONSTRUCTOR);
+  __ bind(&do_call);
   // Set expected number of arguments to zero (not changing rax).
   __ Set(rbx, 0);
-  __ GetBuiltinEntry(rdx, Builtins::CALL_NON_FUNCTION_AS_CONSTRUCTOR);
   __ SetCallKind(rcx, CALL_AS_METHOD);
   __ Jump(masm->isolate()->builtins()->ArgumentsAdaptorTrampoline(),
           RelocInfo::CODE_TARGET);