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1 (* L3 compiler

2 * peephole optimizer

3 * optimizes away redundant insns such as:

4 mov a, b

5 mov a, b

6

7 mov a, b

8 mov b, a

9

10 mov a, a

11

12 neg a

13 neg a

14 * Author: Chris Lu <czl@andrew.cmu.edu>

15 *)

16

17 structure Peephole :> OPTIMIZATION =

18 struct

19 structure X = x86

20

21 (* val peephole : x86.insn list -> x86.insn list *)

22 fun peephole ((insn1 as X.MOV(d1, s1 as (X.REL a,_)))::(insn2 as X.MOV(d2, s2 as (X.REL(a2,b2,m),_)))::l) =

23 if(X.opereq(a2,d1) orelse X.opereq(b2,d1)) then

24 insn1::(peephole (insn2::l))

25 else if(X.opereq(s1,s2) andalso X.opereq (d1,d2)) then

26 peephole (insn2::l)

27 else

28 insn1::(peephole (insn2::l))

29 | peephole ((insn1 as X.MOV(a1,b1))::(insn2 as X.MOV(a2,b2))::l) =

30 if(X.opereq(a1, b1) orelse (X.opereq(a1, a2) andalso X.opereq(b1, b2))) then

31 peephole (insn2::l)

32 else if(X.opereq(a2, b2) orelse (X.opereq(a1, b2) andalso X.opereq(b1, a2))) then

33 peephole (insn1::l)

34 else

35 insn1::(peephole (insn2::l))

36 | peephole (X.MOV (a as (X.REG r,s), (X.CONST 0w0,_))::l) = (X.XOR (a, a))::(peephole l)

37 | peephole ((insn as X.MOV(a,b))::l) = if X.opereq(a, b) then peephole l else insn::(peephole l)

38 | peephole ((insn1 as X.NEG(a))::(insn2 as X.NEG(b))::l) = if X.opereq(a, b) then peephole l else insn1::(peephole (insn2::l))

39 | peephole (X.ADD (_, (X.CONST 0w0,_))::l) = peephole l

40 | peephole (X.SUB (_, (X.CONST 0w0,_))::l) = peephole l

41 (* | peephole (X.CMP ((X.REG r,s), (X.CONST 0w0,_))::l) = (X.TEST ((X.REG r,s), (X.REG r,s)))::(peephole l) *)

42 | peephole ((X.JMP a)::(X.JMP b)::l) = peephole ((X.JMP a)::l) (* What the cock? Yes, we actually generate this. *)

43 | peephole ((X.JMP l1)::(X.LABEL l2)::l) = if (Label.compare (l1,l2) = EQUAL) then (X.LABEL l2)::(peephole l) else (X.JMP l1)::(X.LABEL l2)::(peephole l)

44 | peephole (a::l) = a::(peephole l)

45 | peephole nil = nil

46

47 val optimizer = { shortname = "peephole", description = "Peephole analysis", func = Optimizer.FINAL peephole }

48 end