[turbofan] Add basic support for calling to (a subset of) C functions.

src/compiler/linkage.h

 // 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.
 
 #ifndef V8_COMPILER_LINKAGE_H_
 #define V8_COMPILER_LINKAGE_H_
 
 #include "src/base/flags.h"
 #include "src/compiler/frame.h"
 #include "src/compiler/machine-type.h"
@@ skipping 84 matching lines @@
         callee_saved_registers_(callee_saved_registers),
         flags_(flags),
         debug_name_(debug_name) {
     DCHECK(machine_sig->return_count() == location_sig->return_count());
     DCHECK(machine_sig->parameter_count() == location_sig->parameter_count());
   }
 
   // Returns the kind of this call.
   Kind kind() const { return kind_; }
 
+  // Returns {true} if this descriptor is a call to a C function.
+  bool IsCFunctionCall() const { return kind_ == kCallAddress; }
+
   // Returns {true} if this descriptor is a call to a JSFunction.
   bool IsJSFunctionCall() const { return kind_ == kCallJSFunction; }
 
   // The number of return values from this call.
   size_t ReturnCount() const { return machine_sig_->return_count(); }
 
+  // The number of C parameters to this call.
+  size_t CParameterCount() const { return machine_sig_->parameter_count(); }
+
   // The number of JavaScript parameters to this call, including the receiver
   // object.
   size_t JSParameterCount() const { return js_param_count_; }
 
   // The total number of inputs to this call, which includes the target,
   // receiver, context, etc.
   // TODO(titzer): this should input the framestate input too.
   size_t InputCount() const { return 1 + machine_sig_->parameter_count(); }
 
   size_t FrameStateCount() const { return NeedsFrameState() ? 1 : 0; }
@@ skipping 136 matching lines @@
   CallDescriptor* const incoming_;
 
   DISALLOW_COPY_AND_ASSIGN(Linkage);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LINKAGE_H_