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compile-rtl, II

From: Stefan Israelsson Tampe
Subject: compile-rtl, II
Date: Mon, 15 Oct 2012 16:05:40 +0200

Hi all, Let me suggest another layout of function frames

(arg1, return-address, old-frame, program, arg2 ...)

And the layout of the return is

(ret1, return-address, old-frame, program, ret2 ,....)

and let the local registers be occupied by

fr[0] = arg1
fr[1] = return-address
fr[2] = old-frame
fr[3] = program
fr[4] = arg2

This way we do not need to copy the program field at a tail call and also, we do not need to
move the return value when we do a call e.g.

(f (g x))

can minimally be described by sp = 10

(s-move 10 x)
(f-move 13 g L1)
(call    10 1)
(f-move 13 f L2:)
(call    10 1)
(return 10)

f-moves  : makes sure to prepare a function header
s-moves : adjust the stack to the target of the move

This looks minimally, but the f-move and s-move
variants together with ordinary moves is a flavor for every
value producing instruction, in some way we would need to
add flags to many of the instructions or triple the number of
them. I need to play with this further to understand how to solve this

Also another kind of difficulty will arise, many instructions only take a
value of 256 register positions, we would somehow need to handle the larger
instructions by moving things and this is complicated. Don't know what to do about this yet


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