The code generator is fairly straightforward. Its output is a list-structured representation of assembly code for a hypothetical MacScheme machine.
Only a few optimizations are performed during Pass 4:
LET optimization.
The
real output of pass 4
usually includes nop instructions,
which are removed by an
optional pass
and are ignored by the
assembler
in any case.
Without these nop instructions,
the MacScheme machine assembly code that is generated for the
reverse-map
example is
((17 ( ; lambda *,0,*
(62) ; ; .proc
(19 2) ; ; args= 2
(1 unspecified) ; ; op1 unspecified
(5 ()) ; ; const ()
(15 3) ; ; setreg 3
(32 1001 3) ; ; branch 1001,3
(60 4) ; ; .align 4
(63 1001) ; ; L1001:
(62) ; ; .proc
(58 #(.loop|2 ; ; .proc-doc #(.loop|2
#f 2 #f #f ; ; #f 2 #f #f
(l x))) ; ; (l x))
(14 2 .l|3) ; ; reg 2,.l|3
(1 pair?) ; ; op1 pair?
(33 1004 3) ; ; branchf 1004,3
(22 3) ; ; save 3
(13 0 0) ; ; store 0,0
(13 1 2) ; ; store 1,2
(13 2 3) ; ; store 2,3
(13 3 1) ; ; store 3,1
(14 2 .l|3) ; ; reg 2,.l|3
(1 car) ; ; op1 car
(15 7) ; ; setreg 7
(14 1 .f|1|6) ; ; reg 1,.f|1|6
(15 2) ; ; setreg 2
(16 7 1) ; ; movereg 7,1
(14 2) ; ; reg 2
(23 1007) ; ; setrtn 1007
(21 1) ; ; invoke 1
(60 4) ; ; .align 4
(63 1007) ; ; L1007:
(61) ; ; .cont
(12 0 0) ; ; load 0,0
(12 7 1) ; ; load 7,1
(2 cons 7) ; ; op2 cons,7
(15 3) ; ; setreg 3
(12 1 2) ; ; load 1,2
(10 3) ; ; stack 3
(1 cdr) ; ; op1 cdr
(15 2) ; ; setreg 2
(25 3) ; ; pop 3
(32 1001 3) ; ; branch 1001,3
(63 1004) ; ; L1004:
(14 3 .x|3) ; ; reg 3,.x|3
(26)) ; ; return
0 ; ;
#(reverse-map ; ;
#f 2 #f #f ; ;
(f l))) ; ;
(7 reverse-map) ; setglbl reverse-map
(5 reverse-map) ; const reverse-map
(26)) ; return
This MacScheme machine assembly code is then passed to the assembler for peephole optimization and generation of native code for the real target machine.