[es6] Tail calls support.

src/x64/builtins-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.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/code-factory.h"
 #include "src/codegen.h"
 #include "src/deoptimizer.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 1179 matching lines @@
   __ JumpIfRoot(rax, Heap::kNullValueRootIndex, &no_arguments, Label::kNear);
   __ JumpIfRoot(rax, Heap::kUndefinedValueRootIndex, &no_arguments,
                 Label::kNear);
 
   // 4a. Apply the receiver to the given argArray (passing undefined for
   // new.target).
   __ LoadRoot(rdx, Heap::kUndefinedValueRootIndex);
   __ Jump(masm->isolate()->builtins()->Apply(), RelocInfo::CODE_TARGET);
 
   // 4b. The argArray is either null or undefined, so we tail call without any
-  // arguments to the receiver.
+  // arguments to the receiver. Since we did not create a frame for
+  // Function.prototype.apply() yet, we use a normal Call builtin here.
   __ bind(&no_arguments);
   {
     __ Set(rax, 0);
     __ Jump(masm->isolate()->builtins()->Call(), RelocInfo::CODE_TARGET);
   }
 
   // 4c. The receiver is not callable, throw an appropriate TypeError.
   __ bind(&receiver_not_callable);
   {
     StackArgumentsAccessor args(rsp, 0);
@@ skipping 43 matching lines @@
     __ bind(&loop);
     __ movp(rbx, args.GetArgumentOperand(1));
     __ movp(args.GetArgumentOperand(0), rbx);
     __ decp(rcx);
     __ j(not_zero, &loop);              // While non-zero.
     __ DropUnderReturnAddress(1, rbx);  // Drop one slot under return address.
     __ decp(rax);  // One fewer argument (first argument is new receiver).
   }
 
   // 4. Call the callable.
+  // Since we did not create a frame for Function.prototype.call() yet,
+  // we use a normal Call builtin here.
   __ Jump(masm->isolate()->builtins()->Call(), RelocInfo::CODE_TARGET);
 }
 
 
 void Builtins::Generate_ReflectApply(MacroAssembler* masm) {
   // ----------- S t a t e -------------
   //  -- rax     : argc
   //  -- rsp[0]  : return address
   //  -- rsp[8]  : argumentsList
   //  -- rsp[16] : thisArgument
@@ skipping 761 matching lines @@
 
   // Dispatch to Call or Construct depending on whether new.target is undefined.
   {
     __ CompareRoot(rdx, Heap::kUndefinedValueRootIndex);
     __ j(equal, masm->isolate()->builtins()->Call(), RelocInfo::CODE_TARGET);
     __ Jump(masm->isolate()->builtins()->Construct(), RelocInfo::CODE_TARGET);
   }
 }
 
 
+namespace {
+
+// Drops top JavaScript frame and an arguments adaptor frame below it (if
+// present) preserving all the arguments prepared for current call.
+// Does nothing if debugger is currently active.
+// ES6 14.6.3. PrepareForTailCall
+//
+// Stack structure for the function g() tail calling f():
+//
+// ------- Caller frame: -------
+// |  ...
+// |  g()'s arg M
+// |  ...
+// |  g()'s arg 1
+// |  g()'s receiver arg
+// |  g()'s caller pc
+// ------- g()'s frame: -------
+// |  g()'s caller fp      <- fp
+// |  g()'s context
+// |  function pointer: g
+// |  -------------------------
+// |  ...
+// |  ...
+// |  f()'s arg N
+// |  ...
+// |  f()'s arg 1
+// |  f()'s receiver arg
+// |  f()'s caller pc      <- sp
+// ----------------------
+//
+void PrepareForTailCall(MacroAssembler* masm, Register args_reg,
+                        Register scratch1, Register scratch2,
+                        Register scratch3) {
+  DCHECK(!AreAliased(args_reg, scratch1, scratch2, scratch3));
+  Comment cmnt(masm, "[ PrepareForTailCall");
+
+  // Prepare for tail call only if the debugger is not active.
+  Label done;
+  ExternalReference debug_is_active =
+      ExternalReference::debug_is_active_address(masm->isolate());
+  __ Move(kScratchRegister, debug_is_active);
+  __ cmpb(Operand(kScratchRegister, 0), Immediate(0));
+  __ j(not_equal, &done, Label::kNear);
+
+  // Check if next frame is an arguments adaptor frame.
+  Label no_arguments_adaptor, formal_parameter_count_loaded;
+  __ movp(scratch2, Operand(rbp, StandardFrameConstants::kCallerFPOffset));
+  __ Cmp(Operand(scratch2, StandardFrameConstants::kContextOffset),
+         Smi::FromInt(StackFrame::ARGUMENTS_ADAPTOR));
+  __ j(not_equal, &no_arguments_adaptor, Label::kNear);
+
+  // Drop arguments adaptor frame and load arguments count.
+  __ movp(rbp, scratch2);
+  __ SmiToInteger32(
+      scratch1, Operand(rbp, ArgumentsAdaptorFrameConstants::kLengthOffset));
+  __ jmp(&formal_parameter_count_loaded, Label::kNear);
+
+  __ bind(&no_arguments_adaptor);
+  // Load caller's formal parameter count
+  __ movp(scratch1, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
+  __ movp(scratch1,
+          FieldOperand(scratch1, JSFunction::kSharedFunctionInfoOffset));
+  __ LoadSharedFunctionInfoSpecialField(
+      scratch1, scratch1, SharedFunctionInfo::kFormalParameterCountOffset);
+
+  __ bind(&formal_parameter_count_loaded);
+
+  // Calculate the destination address where we will put the return address
+  // after we drop current frame.
+  Register new_sp_reg = scratch2;
+  __ subp(scratch1, args_reg);
+  __ leap(new_sp_reg, Operand(rbp, scratch1, times_pointer_size,
+                              StandardFrameConstants::kCallerPCOffset));
+
+  if (FLAG_debug_code) {
+    __ cmpp(rsp, new_sp_reg);
+    __ Check(below, kStackAccessBelowStackPointer);
+  }
+
+  // Copy receiver and return address as well.
+  Register count_reg = scratch1;
+  __ leap(count_reg, Operand(args_reg, 2));
+
+  // Copy return address from caller's frame to current frame's return address
+  // to avoid its trashing and let the following loop copy it to the right
+  // place.
+  Register tmp_reg = scratch3;
+  __ movp(tmp_reg, Operand(rbp, StandardFrameConstants::kCallerPCOffset));
+  __ movp(Operand(rsp, 0), tmp_reg);
+
+  // Restore caller's frame pointer now as it could be overwritten by
+  // the copying loop.
+  __ movp(rbp, Operand(rbp, StandardFrameConstants::kCallerFPOffset));
+
+  Operand src(rsp, count_reg, times_pointer_size, 0);
+  Operand dst(new_sp_reg, count_reg, times_pointer_size, 0);
+
+  // Now copy callee arguments to the caller frame going backwards to avoid
+  // callee arguments corruption (source and destination areas could overlap).
+  Label loop, entry;
+  __ jmp(&entry, Label::kNear);
+  __ bind(&loop);
+  __ decp(count_reg);
+  __ movp(tmp_reg, src);
+  __ movp(dst, tmp_reg);
+  __ bind(&entry);
+  __ cmpp(count_reg, Immediate(0));
+  __ j(not_equal, &loop, Label::kNear);
+
+  // Leave current frame.
+  __ movp(rsp, new_sp_reg);
+
+  __ bind(&done);
+}
+}  // namespace
+
+
 // static
 void Builtins::Generate_CallFunction(MacroAssembler* masm,
-                                     ConvertReceiverMode mode) {
+                                     ConvertReceiverMode mode,
+                                     TailCallMode tail_call_mode) {
   // ----------- S t a t e -------------
   //  -- rax : the number of arguments (not including the receiver)
   //  -- rdi : the function to call (checked to be a JSFunction)
   // -----------------------------------
   StackArgumentsAccessor args(rsp, rax);
   __ AssertFunction(rdi);
 
   // ES6 section 9.2.1 [[Call]] ( thisArgument, argumentsList)
   // Check that the function is not a "classConstructor".
   Label class_constructor;
@@ skipping 75 matching lines @@
   }
   __ bind(&done_convert);
 
   // ----------- S t a t e -------------
   //  -- rax : the number of arguments (not including the receiver)
   //  -- rdx : the shared function info.
   //  -- rdi : the function to call (checked to be a JSFunction)
   //  -- rsi : the function context.
   // -----------------------------------
 
+  if (tail_call_mode == TailCallMode::kAllow) {
+    PrepareForTailCall(masm, rax, rbx, rcx, r8);
+  }
+
   __ LoadSharedFunctionInfoSpecialField(
       rbx, rdx, SharedFunctionInfo::kFormalParameterCountOffset);
   ParameterCount actual(rax);
   ParameterCount expected(rbx);
 
   __ InvokeFunctionCode(rdi, no_reg, expected, actual, JUMP_FUNCTION,
                         CheckDebugStepCallWrapper());
 
   // The function is a "classConstructor", need to raise an exception.
   __ bind(&class_constructor);
@@ skipping 84 matching lines @@
     // [[BoundArguments]]), so we need to subtract one for the return address.
     __ decl(rax);
   }
   __ bind(&no_bound_arguments);
 }
 
 }  // namespace
 
 
 // static
-void Builtins::Generate_CallBoundFunction(MacroAssembler* masm) {
+void Builtins::Generate_CallBoundFunctionImpl(MacroAssembler* masm,

[Benedikt Meurer, 2016/01/22 05:23:12]

Nit: No need to add Impl suffix here.

[Igor Sheludko, 2016/01/22 09:48:51]

We have to use a different name here otherwise the compiler will complain about
ambiguity of the &Generate_CallBoundFunction that we have in our macros.

+                                              TailCallMode tail_call_mode) {
   // ----------- S t a t e -------------
   //  -- rax : the number of arguments (not including the receiver)
   //  -- rdi : the function to call (checked to be a JSBoundFunction)
   // -----------------------------------
   __ AssertBoundFunction(rdi);
 
+  if (tail_call_mode == TailCallMode::kAllow) {

[Benedikt Meurer, 2016/01/22 05:23:12]

You don't need to do this here. Just pick the right Call builtin at the end,
depending on tail_call_mode, which will then deconstruct the frame properly,
i.e.

__ Load(rcx, ExternalReference(tail_call_mode == TailCallMode::kAllow ?
Builtins::kTailCall_ReceiverIsAny : Builtins::kCall_ReceiverIsAny,
masm->isolate()));

should do the trick.

[Igor Sheludko, 2016/01/22 09:48:51]

If we do like you suggested that would mean that we will copy the bound
arguments twice. Probably we don't want that.

+    PrepareForTailCall(masm, rax, rbx, rcx, r8);
+  }
+
   // Patch the receiver to [[BoundThis]].
   StackArgumentsAccessor args(rsp, rax);
   __ movp(rbx, FieldOperand(rdi, JSBoundFunction::kBoundThisOffset));
   __ movp(args.GetReceiverOperand(), rbx);
 
   // Push the [[BoundArguments]] onto the stack.
   Generate_PushBoundArguments(masm);
 
   // Call the [[BoundTargetFunction]] via the Call builtin.
   __ movp(rdi, FieldOperand(rdi, JSBoundFunction::kBoundTargetFunctionOffset));
   __ Load(rcx,
           ExternalReference(Builtins::kCall_ReceiverIsAny, masm->isolate()));
   __ leap(rcx, FieldOperand(rcx, Code::kHeaderSize));
   __ jmp(rcx);
 }
 
 
 // static
-void Builtins::Generate_Call(MacroAssembler* masm, ConvertReceiverMode mode) {
+void Builtins::Generate_Call(MacroAssembler* masm, ConvertReceiverMode mode,
+                             TailCallMode tail_call_mode) {
   // ----------- S t a t e -------------
   //  -- rax : the number of arguments (not including the receiver)
   //  -- rdi : the target to call (can be any Object)
   // -----------------------------------
   StackArgumentsAccessor args(rsp, rax);
 
   Label non_callable, non_function, non_smi;
   __ JumpIfSmi(rdi, &non_callable);
   __ bind(&non_smi);
   __ CmpObjectType(rdi, JS_FUNCTION_TYPE, rcx);
-  __ j(equal, masm->isolate()->builtins()->CallFunction(mode),
+  __ j(equal, masm->isolate()->builtins()->CallFunction(mode, tail_call_mode),
        RelocInfo::CODE_TARGET);
   __ CmpInstanceType(rcx, JS_BOUND_FUNCTION_TYPE);
-  __ j(equal, masm->isolate()->builtins()->CallBoundFunction(),
+  __ j(equal, masm->isolate()->builtins()->CallBoundFunction(tail_call_mode),
        RelocInfo::CODE_TARGET);
   __ CmpInstanceType(rcx, JS_PROXY_TYPE);
   __ j(not_equal, &non_function);
 
+  // 0. Prepare for tail call if necessary.
+  if (tail_call_mode == TailCallMode::kAllow) {
+    PrepareForTailCall(masm, rax, rbx, rcx, r8);
+  }
+
   // 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()));
 
   // 2. Call to something else, which might have a [[Call]] internal method (if
   // not we raise an exception).
   __ bind(&non_function);
   // Check if target has a [[Call]] internal method.
   __ testb(FieldOperand(rcx, Map::kBitFieldOffset),
            Immediate(1 << Map::kIsCallable));
   __ j(zero, &non_callable, Label::kNear);
   // Overwrite the original receiver with the (original) target.
   __ movp(args.GetReceiverOperand(), rdi);
   // Let the "call_as_function_delegate" take care of the rest.
   __ LoadNativeContextSlot(Context::CALL_AS_FUNCTION_DELEGATE_INDEX, rdi);
   __ Jump(masm->isolate()->builtins()->CallFunction(
-              ConvertReceiverMode::kNotNullOrUndefined),
+              ConvertReceiverMode::kNotNullOrUndefined, tail_call_mode),
           RelocInfo::CODE_TARGET);
 
   // 3. Call to something that is not callable.
   __ bind(&non_callable);
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
     __ Push(rdi);
     __ CallRuntime(Runtime::kThrowCalledNonCallable);
   }
 }
@@ skipping 290 matching lines @@
   __ ret(0);
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64