want to port JIT to MIPS - IEEE ques

want to port JIT to MIPS - IEEE ques 

http://marc.info/?l=webkit-dev&m=123362331100323&w=2 

 In Generator::generateEnter(), there is comment "On gcc the function is regparm(3)...", how to understand that?
 WREC JIT generates a function with a C calling convention that implements the regular expression.  The entry and exit 
from the function are generated by the generateEnter() and generateReturn*() methods. 
 On OS X x86, the JIT generated function implements a regparm(3) calling convention (see WREC.h, the generated code is called through a CompiledRegExp function pointer).

The function has no argument, why we peek four arguments from stack(input,output,length,index)?
>  These calls are not peeking values from the stack at the time they are called; they are emitting JIT code that will 
read values from the stack, when the JIT function has been generated and is run.
>  The JIT generated regular expression function is passed these four arguments (again see WREC.h).