StubCallInterfaceDescriptor takes a context register.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 425683c4fb4d2626736f6cd81bce88385163003a..c5858c0534d7b2448341096bdc4557a060adcc96 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -2321,12 +2321,13 @@ class HCallWithDescriptor V8_FINAL : public HInstruction {
  public:
   static HCallWithDescriptor* New(Zone* zone, HValue* context,
       HValue* target,
+      HValue* call_context,
       int argument_count,
-      const CallInterfaceDescriptor* descriptor,
+      const InterfaceDescriptor* descriptor,
       const Vector<HValue*>& operands) {
     ASSERT(operands.length() == descriptor->environment_length());
     HCallWithDescriptor* res =
-        new(zone) HCallWithDescriptor(target, argument_count,
+        new(zone) HCallWithDescriptor(target, call_context, argument_count,
                                       descriptor, operands, zone);
     return res;
   }
@@ -2338,12 +2339,18 @@ class HCallWithDescriptor V8_FINAL : public HInstruction {
     return values_[index];
   }
 
+  int FirstDescriptorOperandIndex() const {
+    // Our Operand array contains target and possibly context before the
+    // descriptor parameters.
+    return descriptor_->needs_context_register() ? 2 : 1;

[danno, 2014/07/15 07:48:31]

Is it possible to roll this into the descriptor, too? You might need two calls:
GetParameterRepresentation and  GetOperandParameterRepresentation that do the
implicit +1 if there is a context register. But that moves the logic out of this
call class.

+  }
+
   virtual Representation RequiredInputRepresentation(
       int index) V8_FINAL V8_OVERRIDE {
-    if (index == 0) {
+    if (index < FirstDescriptorOperandIndex()) {
       return Representation::Tagged();
     } else {
-      int par_index = index - 1;
+      int par_index = index - FirstDescriptorOperandIndex();
       ASSERT(par_index < descriptor_->environment_length());
       return descriptor_->GetParameterRepresentation(par_index);
     }
@@ -2363,7 +2370,7 @@ class HCallWithDescriptor V8_FINAL : public HInstruction {
     return -argument_count_;
   }
 
-  const CallInterfaceDescriptor* descriptor() const {
+  const InterfaceDescriptor* descriptor() const {
     return descriptor_;
   }
 
@@ -2371,19 +2378,29 @@ class HCallWithDescriptor V8_FINAL : public HInstruction {
     return OperandAt(0);
   }
 
+  HValue* context() {
+    ASSERT(descriptor_->needs_context_register());
+    return OperandAt(1);
+  }
+
   virtual OStream& PrintDataTo(OStream& os) const V8_OVERRIDE;  // NOLINT
 
  private:
   // The argument count includes the receiver.
   HCallWithDescriptor(HValue* target,
+                      HValue* context,
                       int argument_count,
-                      const CallInterfaceDescriptor* descriptor,
+                      const InterfaceDescriptor* descriptor,
                       const Vector<HValue*>& operands,
                       Zone* zone)
     : descriptor_(descriptor),
-      values_(descriptor->environment_length() + 1, zone) {
+      values_(value_array_length(descriptor), zone) {
     argument_count_ = argument_count;
     AddOperand(target, zone);
+    if (descriptor->needs_context_register()) {
+      ASSERT(context != NULL);
+      AddOperand(context, zone);
+    }
     for (int i = 0; i < operands.length(); i++) {
       AddOperand(operands[i], zone);
     }
@@ -2391,6 +2408,11 @@ class HCallWithDescriptor V8_FINAL : public HInstruction {
     this->SetAllSideEffects();
   }
 
+  static int value_array_length(const InterfaceDescriptor* descriptor) {
+    int extra_operands = descriptor->needs_context_register() ? 2 : 1;
+    return descriptor->environment_length() + extra_operands;

[danno, 2014/07/15 07:48:31]

Similar to GetParameterRepresentation, you will need two version of
GetEnvironmentLength

+  }
+
   void AddOperand(HValue* v, Zone* zone) {
     values_.Add(NULL, zone);
     SetOperandAt(values_.length() - 1, v);
@@ -2401,7 +2423,7 @@ class HCallWithDescriptor V8_FINAL : public HInstruction {
     values_[index] = value;
   }
 
-  const CallInterfaceDescriptor* descriptor_;
+  const InterfaceDescriptor* descriptor_;
   ZoneList<HValue*> values_;
   int argument_count_;
 };