Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!POSTGRES.BERKELEY.EDU!dillon
From: dillon@POSTGRES.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga compiler optimizing test
Message-ID: <8903051103.AA00179@postgres.Berkeley.EDU>
Date: 5 Mar 89 11:03:40 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 18

>Why would an optimizing compiler put `link a5, 0000' and 'unlnk a5'
>instructions into a subroutine that needed no local variables?

	(1) So A5 can be used to referenced arguments

	(2) So a debugger can backtrace the stack frame.

	Apart from that, there is no reason to use link/unlk at all.  If
you want to talk about optimization, one can cut the call-return overhead by
half or more by:

	(1) caller passes the return address in a register and jmp's or bra's
	    to the routine instead of jsr'ing

	(2) callee pops caller's arguments (it can pop the args and free up
	    its own stack (local vars) in one instruction.. an add).

							-Matt