[turbofan] Implement tail calls with differing stack parameter counts

src/compiler/ast-graph-builder.cc

 // Copyright 2014 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/compiler/ast-graph-builder.h"
 
 #include "src/compiler.h"
 #include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
 #include "src/compiler/js-type-feedback.h"
@@ skipping 2583 matching lines @@
     ast_context()->ProduceValue(jsgraph()->TheHoleConstant());
     return SetStackOverflow();
   }
 
   // Evaluate all arguments to the runtime call.
   ZoneList<Expression*>* args = expr->arguments();
   VisitForValues(args);
 
   // Create node to perform the runtime call.
   Runtime::FunctionId functionId = function->function_id;
-  const Operator* call = javascript()->CallRuntime(functionId, args->length());
+  // Outer-most frame of calls into native function chains must have a frame in
+  // the stack crawl.
+  TailCallMode mode =

[Benedikt Meurer, 2015/07/30 06:47:24]

IMHO this will be highly confusing and might be a source of weird bugs in the
future. By just looking at a tail call site in a .js file you will be mostly
unable to tell whether it is actually a tailcall to the runtime or a regular
call. I'd really prefer to have this explicit at the tail call site so people
are aware of what they are doing, just like we do in the native code stubs,
where we have __ TailCallRuntime and __ CallRuntime.

+      info()->shared_info()->native() ? NO_TAIL_CALLS : ALLOW_TAIL_CALLS;
+  const Operator* call =
+      javascript()->CallRuntime(functionId, args->length(), mode);
   FrameStateBeforeAndAfter states(this, expr->CallId());
   Node* value = ProcessArguments(call, args->length());
   states.AddToNode(value, expr->id(), ast_context()->GetStateCombine());
   ast_context()->ProduceValue(value);
 }
 
 
 void AstGraphBuilder::VisitUnaryOperation(UnaryOperation* expr) {
   switch (expr->op()) {
     case Token::DELETE:
@@ skipping 1701 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8