First take on custom call generators.

src/ia32/codegen-ia32.h

Index: src/ia32/codegen-ia32.h
diff --git a/src/ia32/codegen-ia32.h b/src/ia32/codegen-ia32.h
index b0adebe840eac535ac5d9d9ccee2c2785b26983d..f7ec0b580ef5ef9d1f5d2e47ec827f97c8f7bbd3 100644
--- a/src/ia32/codegen-ia32.h
+++ b/src/ia32/codegen-ia32.h
@@ -977,6 +977,42 @@ class NumberToStringStub: public CodeStub {
 };
 
 
+class RecordWriteStub : public CodeStub {
+ public:
+  RecordWriteStub(Register object, Register addr, Register scratch)
+      : object_(object), addr_(addr), scratch_(scratch) { }
+
+  void Generate(MacroAssembler* masm);
+
+ private:
+  Register object_;
+  Register addr_;
+  Register scratch_;
+
+#ifdef DEBUG
+  void Print() {
+    PrintF("RecordWriteStub (object reg %d), (addr reg %d), (scratch reg %d)\n",
+           object_.code(), addr_.code(), scratch_.code());
+  }
+#endif
+
+  // Minor key encoding in 12 bits of three registers (object, address and
+  // scratch) OOOOAAAASSSS.
+  class ScratchBits: public BitField<uint32_t, 0, 4> {};
+  class AddressBits: public BitField<uint32_t, 4, 4> {};
+  class ObjectBits: public BitField<uint32_t, 8, 4> {};
+
+  Major MajorKey() { return RecordWrite; }
+
+  int MinorKey() {
+    // Encode the registers.
+    return ObjectBits::encode(object_.code()) |
+           AddressBits::encode(addr_.code()) |
+           ScratchBits::encode(scratch_.code());
+  }
+};
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_IA32_CODEGEN_IA32_H_