WIP context-allocation for “this” in arrow functions

src/x64/full-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
@@ skipping 95 matching lines @@
 
 #ifdef DEBUG
   if (strlen(FLAG_stop_at) > 0 &&
       info->function()->name()->IsUtf8EqualTo(CStrVector(FLAG_stop_at))) {
     __ int3();
   }
 #endif
 
   // Sloppy mode functions and builtins need to replace the receiver with the
   // global proxy when called as functions (without an explicit receiver
-  // object).
-  if (info->strict_mode() == SLOPPY && !info->is_native()) {
+  // object). Arrow functions need to replace the receiver with the receiver
+  // of the parent scope, so this does not need to be done for those.

[wingo, 2015/01/15 10:09:06]

It's not necessarily the receiver from the parent scope -- the parent scope
could be a block scope, or another arrow function; anyway let's be more precise
with comments :)

[aperez, 2015/01/15 16:58:03]

Done.

+  if (info->strict_mode() == SLOPPY && !info->is_native() &&
+      !info->function()->is_arrow()) {
     Label ok;
     // +1 for return address.
     StackArgumentsAccessor args(rsp, info->scope()->num_parameters());
     __ movp(rcx, args.GetReceiverOperand());
 
     __ CompareRoot(rcx, Heap::kUndefinedValueRootIndex);
     __ j(not_equal, &ok, Label::kNear);
 
     __ movp(rcx, GlobalObjectOperand());
     __ movp(rcx, FieldOperand(rcx, GlobalObject::kGlobalProxyOffset));
 
     __ movp(args.GetReceiverOperand(), rcx);
 
     __ bind(&ok);
   }
 
   // Open a frame scope to indicate that there is a frame on the stack.  The
   // MANUAL indicates that the scope shouldn't actually generate code to set up
   // the frame (that is done below).
   FrameScope frame_scope(masm_, StackFrame::MANUAL);
 
   info->set_prologue_offset(masm_->pc_offset());
   __ Prologue(info->IsCodePreAgingActive());
   info->AddNoFrameRange(0, masm_->pc_offset());
 
+  // For arrow functions the value of the receiver is stored in the context,
+  // so in the case of a function that actually uses "this", the receiver is
+  // replaced by the one resulting from looking it up in the context.
+  if (info->function()->is_arrow() && info->scope()->uses_this()) {
+    DCHECK(info->scope()->scope_type() == ARROW_SCOPE);
+    Comment cmnt(masm_, "[ Patch receiver for arrow function");
+    StackArgumentsAccessor args(rbp, info->scope()->num_parameters());
+    __ Push(rsi);  // Context
+    __ Push(isolate()->factory()->this_string());
+    __ CallRuntime(Runtime::kLoadLookupSlot, 2);
+    __ movp(args.GetReceiverOperand(), rax);
+  }
+
   { Comment cmnt(masm_, "[ Allocate locals");
     int locals_count = info->scope()->num_stack_slots();
     // Generators allocate locals, if any, in context slots.
     DCHECK(!info->function()->is_generator() || locals_count == 0);
     if (locals_count == 1) {
       __ PushRoot(Heap::kUndefinedValueRootIndex);
     } else if (locals_count > 1) {
       if (locals_count >= 128) {
         Label ok;
         __ movp(rcx, rsp);
@@ skipping 47 matching lines @@
       __ Push(rdi);
       __ CallRuntime(Runtime::kNewFunctionContext, 1);
     }
     function_in_register = false;
     // Context is returned in rax.  It replaces the context passed to us.
     // It's saved in the stack and kept live in rsi.
     __ movp(rsi, rax);
     __ movp(Operand(rbp, StandardFrameConstants::kContextOffset), rax);
 
     // Copy any necessary parameters into the context.
+    if (info->scope()->inner_uses_this()) {

[wingo, 2015/01/15 10:09:06]

Let's factor this into the loop below

[aperez, 2015/01/15 16:58:03]

Done.

+      Comment cmnt(masm_, "[ Save receiver in context for arrow function");
+      DCHECK(info->scope()->receiver()->IsContextSlot());
+      // Put the "this" in the context after the rest of the function
+      // parameters, to avoid having to change the case that handles those.
+      int parameter_offset = StandardFrameConstants::kCallerSPOffset +
+          info->scope()->num_parameters() * kPointerSize;
+      __ movp(rax, Operand(rbp, parameter_offset));
+
+      // Store it in the context.
+      int context_offset = Context::SlotOffset(scope()->receiver()->index());
+      __ movp(Operand(rsi, context_offset), rax);
+
+      if (need_write_barrier) {
+        __ RecordWriteContextSlot(
+            rsi, context_offset, rax, rbx, kDontSaveFPRegs);
+      } else if (FLAG_debug_code) {
+        Label done;
+        __ JumpIfInNewSpace(rsi, rax, &done, Label::kNear);
+        __ Abort(kExpectedNewSpaceObject);
+        __ bind(&done);
+      }
+    }
+
     int num_parameters = info->scope()->num_parameters();
     for (int i = 0; i < num_parameters; i++) {
       Variable* var = scope()->parameter(i);
       if (var->IsContextSlot()) {
         int parameter_offset = StandardFrameConstants::kCallerSPOffset +
             (num_parameters - 1 - i) * kPointerSize;
         // Load parameter from stack.
         __ movp(rax, Operand(rbp, parameter_offset));
         // Store it in the context.
         int context_offset = Context::SlotOffset(var->index());
@@ skipping 2494 matching lines @@
 
   CallICState::CallType call_type =
       callee->IsVariableProxy() ? CallICState::FUNCTION : CallICState::METHOD;
   // Get the target function.
   if (call_type == CallICState::FUNCTION) {
     { StackValueContext context(this);
       EmitVariableLoad(callee->AsVariableProxy());
       PrepareForBailout(callee, NO_REGISTERS);
     }
     // Push undefined as receiver. This is patched in the method prologue if it
-    // is a sloppy mode method.
+    // is a sloppy mode method, or by the function prologue it is an arrow

[wingo, 2015/01/15 10:09:06]

"if it is"

[aperez, 2015/01/15 16:58:03]

Done.

+    // function.
     __ Push(isolate()->factory()->undefined_value());
   } else {
     // Load the function from the receiver.
     DCHECK(callee->IsProperty());
     DCHECK(!callee->AsProperty()->IsSuperAccess());
     __ movp(LoadDescriptor::ReceiverRegister(), Operand(rsp, 0));
     EmitNamedPropertyLoad(callee->AsProperty());
     PrepareForBailoutForId(callee->AsProperty()->LoadId(), TOS_REG);
     // Push the target function under the receiver.
     __ Push(Operand(rsp, 0));
@@ skipping 2458 matching lines @@
   DCHECK_EQ(isolate->builtins()->OsrAfterStackCheck()->entry(),
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64