[snipe.git] / codegen / solidify.sml

(* L3 Compiler
 * Takes a list of mappings of temporaries to colors and a pseudoasm listing,
 * then produces x86 code.
 * Author: Chris Lu <czl@andrew.cmu.edu>
 * Author: Joshua Wise <jwise@andrew.cmu.edu>
 *)

signature SOLIDIFY =
sig
  type colorings = (Temp.temp * int) list
  type asm = Blarg.insn list
  
  val solidify : colorings -> asm -> asm
end

structure Solidify :> SOLIDIFY =
struct
  structure X = Blarg
  structure T = Temp
  
  type colorings = (Temp.temp * int) list
  type asm = Blarg.insn list
  
  exception Spilled

  structure TempMap = SplayMapFn(struct
                                   type ord_key = Temp.temp
                                   val compare = Temp.compare
                                 end)
  structure Tm = Temp

  fun solidify (regmap : colorings) (instrs : asm) : asm =
    let
      (* r11 and r12 is reserved for spilling *)
      val maxreg = X.regtonum X.R10
      fun numtoreg n =
          if (n > maxreg)
          then raise Spilled
          else X.numtoreg n

      val tempnums = List.foldr (fn ((t,n),b) => TempMap.insert(b,t,n)) (TempMap.empty) regmap
      fun temptonum (t: T.temp) : int = valOf (TempMap.find (tempnums, t))

      fun temptoreg (t: T.temp) : Blarg.reg =
        numtoreg (temptonum t)          
        handle Option => raise ErrorMsg.InternalError ("Uncolored temp "^(Temp.name t)^", agh!")

      val spillreg1 = X.R12
      val spillreg2 = X.R11

      (* Determine which need to be saved. *)
      val opsused = (map (fn (_, n) => X.REG (numtoreg n handle Spilled => X.R12)) regmap) @ [X.REG X.R11]
      val saveregs = X.OperSet.intersection (
        X.OperSet.addList (X.OperSet.empty, opsused),
        X.OperSet.addList (
          X.OperSet.empty,
          [X.REG X.R7,
           X.REG X.R8,
           X.REG X.R9,
           X.REG X.R10,
           X.REG X.R11,
           X.REG X.R12]))
      val savelist = X.OperSet.listItems saveregs
      val nsave = length savelist

      val numreg = foldr (Int.max) 0 (map (fn (_, n) => n) regmap)    (* Number of registers used. *)
      val nspilled = Int.max (numreg - maxreg, 0)    (* Number of spilled registers. *)
      fun isspilled (X.TEMP temp) = (temptonum temp) > maxreg    (* Whether a register is spilled *)
        | isspilled (X.STACKARG _) = true
        | isspilled _ = false

      val stacksz = (nspilled + nsave) * 1
      fun stackpos (reg: int) = stacksz - (reg - maxreg + nsave) * 1    (* Stack position of some register number *)

      val prologue =
        [X.INSN (X.AL, X.MOVLIT (X.REG X.R4, Word.fromInt stacksz)),
         X.INSN (X.AL, X.SUB (X.REG X.SP, X.REG X.R4))] @
        (List.concat
          (ListPair.map
            (fn (num, reg) =>
              [X.INSN (X.AL, X.MOVLIT (X.REG X.R4, Word.fromInt (stacksz - 1*(num+1)))),
               X.INSN (X.AL, X.ADD (X.REG X.R4, X.REG X.SP)),
               X.INSN (X.AL, X.STO (X.REG X.R4, reg))])
            (List.tabulate (nsave, fn x => x), savelist)
          )
        )
      val epilogue =
        (List.concat
          (ListPair.map
            (fn (num, reg) =>
              [X.INSN (X.AL, X.MOVLIT (X.REG X.R4, Word.fromInt (stacksz - 1*(num+1)))),
               X.INSN (X.AL, X.ADD (X.REG X.R4, X.REG X.SP)),
               X.INSN (X.AL, X.LDR (reg, X.REG X.R4))])
            (List.tabulate (nsave, fn x => x), savelist)
          )
        ) @
        [X.INSN (X.AL, X.MOVLIT (X.REG X.R4, Word.fromInt stacksz)),
         X.INSN (X.AL, X.ADD (X.REG X.SP, X.REG X.R4))]
      val endlbl = Label.new()

      fun spill (X.TEMP temp, xreg: Blarg.reg) =    (* Spill a register if need be. *)
            let
              val base = X.REG X.SP
              val offs = Word.fromInt (stackpos (temptonum temp))
            in
              if (isspilled (X.TEMP temp))
                then raise ErrorMsg.InternalError "unspill not supported" (*[X.MOV ((X.REL (base, offs, 0w1), Tm.Quad), (X.REG xreg, Tm.Quad))]*)
                else nil
            end
        | spill (X.STACKARG _, _) = raise ErrorMsg.InternalError "Cannot spill to a stack arg"
        | spill _ = nil        (* Nothing else can be spilled. *)
      fun unspill (X.TEMP temp, xreg: Blarg.reg) =    (* Unspill a register if need be. *)
            let
              val base = X.REG X.SP
              val offs = Word.fromInt (stackpos (temptonum temp))
            in
              if (isspilled (X.TEMP temp))
                then raise ErrorMsg.InternalError "unspill not supported" (*[X.MOV ((X.REG xreg, Tm.Quad), (X.REL (base, offs, 0w1), Tm.Quad))]*)
                else nil
            end
        | unspill (X.STACKARG arg, xreg) =
            let
              val base = X.REG X.SP
              val offs = Word.fromInt (stacksz + 8 + (arg * 8))
            in
              (*[X.MOV ((X.REG xreg, s), (X.REL (base, offs, 0w1), s))]*)
              raise ErrorMsg.InternalError "unspill from stack not supported"
            end
        | unspill _ = nil

      fun unspill_ops (op1, op2) =
        case (isspilled op1, isspilled op2)
        of (false, false) => []
         | (true, false) => unspill (op1, spillreg1)
         | (false, true) => unspill (op2, spillreg2)
         | (true, true)  => unspill (op1, spillreg1) @ unspill (op2, spillreg2)
      
      fun respill_ops (op1, op2) =
        case (isspilled op1, isspilled op2) (* no instruction writes back to op2 *)
        of (false, _) => []
         | (true, _) => spill (op1, spillreg1)
      
      fun real_op1 op1 =
        case op1
        of (X.TEMP temp) => if isspilled op1
                            then (X.REG spillreg1)
                            else X.REG (temptoreg temp)
         | (X.STACKARG arg) => X.REG spillreg1
         | r => r
      
      fun real_ops (op1, op2) =
        (case op1
         of (X.TEMP temp) => if isspilled op1
                             then (X.REG spillreg1)
                             else X.REG (temptoreg temp)
          | (X.STACKARG arg) => X.REG spillreg1
          | r => r,
        case op2
         of (X.TEMP temp) => if isspilled op2
                             then (X.REG spillreg2)
                             else X.REG (temptoreg temp)
          | (X.STACKARG arg) => X.REG spillreg2
          | r => r)

      fun whack_insn (pred, insn, op1, op2) =
        (map (fn i => X.INSN (pred, i)) (unspill_ops (op1, op2))) @
        [ X.INSN (pred, insn (real_ops (op1, op2))) ] @
        (map (fn i => X.INSN (pred, i)) (respill_ops (op1, op2)))

      fun transform (X.DIRECTIVE s) = [X.DIRECTIVE s]
        | transform (X.COMMENT s) = [X.COMMENT s]
        | transform (X.LABEL l) = [X.LABEL l]
        | transform (X.LIVEIGN a) = transform a
        
        (* god the special cases are going to suck *)
        | transform (X.INSN (pred, X.MOVLIT (op1, w))) =
            [ X.INSN (pred, X.MOVLIT (real_op1 op1, w)) ] @
            (if isspilled op1
             then spill (op1, spillreg1)
             else [])
        | transform (X.INSN (pred, X.MOVSYM (op1, w))) =
            [ X.INSN (pred, X.MOVSYM (real_op1 op1, w)) ] @
            (if isspilled op1
             then spill (op1, spillreg1)
             else [])
        | transform (X.INSN (pred, X.MOVSTR (op1, w))) =
            [ X.INSN (pred, X.MOVSTR (real_op1 op1, w)) ] @
            (if isspilled op1
             then spill (op1, spillreg1)
             else [])
        | transform (X.INSN (pred, X.MOVLBL (op1, w))) =
            [ X.INSN (pred, X.MOVLBL (real_op1 op1, w)) ] @
            (if isspilled op1
             then spill (op1, spillreg1)
             else [])
        
        (* and here comes the boilerplate *)
        | transform (X.INSN (pred, X.LDR (op1, op2))) =  whack_insn (pred, X.LDR, op1, op2)
        | transform (X.INSN (pred, X.STO (op1, op2))) =  whack_insn (pred, X.STO, op1, op2)
        | transform (X.INSN (pred, X.MOV (op1, op2))) =  whack_insn (pred, X.MOV, op1, op2)
        | transform (X.INSN (pred, X.MOVS (op1, op2))) = whack_insn (pred, X.MOVS, op1, op2)
        | transform (X.INSN (pred, X.ADD (op1, op2))) =  whack_insn (pred, X.ADD, op1, op2)
        | transform (X.INSN (pred, X.ADDS (op1, op2))) = whack_insn (pred, X.ADDS, op1, op2)
        | transform (X.INSN (pred, X.SUB (op1, op2))) =  whack_insn (pred, X.SUB, op1, op2)
        | transform (X.INSN (pred, X.SUBS (op1, op2))) = whack_insn (pred, X.SUBS, op1, op2)
        | transform (X.INSN (pred, X.AND (op1, op2))) =  whack_insn (pred, X.AND, op1, op2)
        | transform (X.INSN (pred, X.ANDS (op1, op2))) = whack_insn (pred, X.ANDS, op1, op2)
        | transform (X.INSN (pred, X.NOT (op1, op2))) =  whack_insn (pred, X.NOT, op1, op2)
        | transform (X.INSN (pred, X.NOTS (op1, op2))) = whack_insn (pred, X.NOTS, op1, op2)
        | transform (X.INSN (pred, X.PUSH (op1, op2))) = if isspilled op2
                                                         then raise ErrorMsg.InternalError "PUSH on spilled op2 is not possible"
                                                         else [ X.INSN (pred, X.PUSH (real_ops (op1, op2))) ]
        | transform (X.INSN (pred, X.POP (X.REG X.SP, X.REG X.PC))) = [ X.INSN (pred, X.MOVLBL (X.REG X.PC, endlbl)) ] (* optimize epilogue? *)
        | transform (X.INSN (pred, X.POP (op1, op2))) =  if isspilled op2
                                                         then raise ErrorMsg.InternalError "POP on spilled op2 is not possible"
                                                         else [ X.INSN (pred, X.POP (real_ops (op1, op2))) ]
        | transform (X.INSN (pred, X.CALL (op1, op2, i))) =  if isspilled op2
                                                             then raise ErrorMsg.InternalError "CALL on spilled op2 is not possible"
                                                             else [ X.INSN (pred, X.CALL ((fn (x, y) => (x, y, i)) (real_ops (op1, op2)))) ]
        | transform (X.INSN (pred, X.SHR (op1, op2))) =  whack_insn (pred, X.SHR, op1, op2)
        | transform (X.INSN (pred, X.SHL (op1, op2))) =  whack_insn (pred, X.SHL, op1, op2)
        (*| transform _ = raise ErrorMsg.InternalError "unimplemented"*)
    in
      (*if (nsave < 2) then
        List.concat (prologue :: (map transform instrs))
      else
      *)
      List.concat (prologue ::
                   ((map transform instrs) @
                    [[X.LABEL endlbl],
                     epilogue,
                     [X.INSN (X.AL, X.POP (X.REG X.SP, X.REG X.PC))]
                    ]
                   )
                  )
    end
end
Commit	Line	Data
6ade8b0a	1	(* L3 Compiler
12aa4087 JW	2	* Takes a list of mappings of temporaries to colors and a pseudoasm listing,
12aa4087 JW	3	* then produces x86 code.
0a24e44d	4	* Author: Chris Lu <czl@andrew.cmu.edu>
12aa4087 JW	5	* Author: Joshua Wise <jwise@andrew.cmu.edu>
	6	*)
	7
	8	signature SOLIDIFY =
	9	sig
	10	type colorings = (Temp.temp * int) list
c2b45b36	11	type asm = Blarg.insn list
12aa4087 JW	12
	13	val solidify : colorings -> asm -> asm
	14	end
	15
	16	structure Solidify :> SOLIDIFY =
	17	struct
c2b45b36	18	structure X = Blarg
12aa4087 JW	19	structure T = Temp
	20
	21	type colorings = (Temp.temp * int) list
c2b45b36	22	type asm = Blarg.insn list
12aa4087 JW	23
12aa4087 JW	24	exception Spilled
5c79bb68 JW	25
	26	structure TempMap = SplayMapFn(struct
	27	type ord_key = Temp.temp
	28	val compare = Temp.compare
	29	end)
	30	structure Tm = Temp
	31
12aa4087 JW	32	fun solidify (regmap : colorings) (instrs : asm) : asm =
12aa4087 JW	33	let
c2b45b36 JW	34	(* r11 and r12 is reserved for spilling *)
c2b45b36 JW	35	val maxreg = X.regtonum X.R10
12aa4087 JW	36	fun numtoreg n =
	37	if (n > maxreg)
	38	then raise Spilled
	39	else X.numtoreg n
1144856b	40
5c79bb68 JW	41	val tempnums = List.foldr (fn ((t,n),b) => TempMap.insert(b,t,n)) (TempMap.empty) regmap
	42	fun temptonum (t: T.temp) : int = valOf (TempMap.find (tempnums, t))
	43
c2b45b36	44	fun temptoreg (t: T.temp) : Blarg.reg =
12aa4087	45	numtoreg (temptonum t)
c2b45b36	46	handle Option => raise ErrorMsg.InternalError ("Uncolored temp "^(Temp.name t)^", agh!")
6ade8b0a	47
c2b45b36 JW	48	val spillreg1 = X.R12
c2b45b36 JW	49	val spillreg2 = X.R11
6ade8b0a JW	50
6ade8b0a JW	51	(* Determine which need to be saved. *)
c2b45b36	52	val opsused = (map (fn (_, n) => X.REG (numtoreg n handle Spilled => X.R12)) regmap) @ [X.REG X.R11]
6ade8b0a JW	53	val saveregs = X.OperSet.intersection (
	54	X.OperSet.addList (X.OperSet.empty, opsused),
	55	X.OperSet.addList (
	56	X.OperSet.empty,
c2b45b36 JW	57	[X.REG X.R7,
	58	X.REG X.R8,
	59	X.REG X.R9,
	60	X.REG X.R10,
	61	X.REG X.R11,
	62	X.REG X.R12]))
6ade8b0a JW	63	val savelist = X.OperSet.listItems saveregs
	64	val nsave = length savelist
	65
1144856b JW	66	val numreg = foldr (Int.max) 0 (map (fn (_, n) => n) regmap) (* Number of registers used. *)
1144856b JW	67	val nspilled = Int.max (numreg - maxreg, 0) (* Number of spilled registers. *)
c2b45b36 JW	68	fun isspilled (X.TEMP temp) = (temptonum temp) > maxreg (* Whether a register is spilled *)
c2b45b36 JW	69	\| isspilled (X.STACKARG _) = true
12aa4087	70	\| isspilled _ = false
5c79bb68	71
c2b45b36 JW	72	val stacksz = (nspilled + nsave) * 1
c2b45b36 JW	73	fun stackpos (reg: int) = stacksz - (reg - maxreg + nsave) * 1 (* Stack position of some register number *)
6ade8b0a JW	74
6ade8b0a JW	75	val prologue =
c2b45b36 JW	76	[X.INSN (X.AL, X.MOVLIT (X.REG X.R4, Word.fromInt stacksz)),
	77	X.INSN (X.AL, X.SUB (X.REG X.SP, X.REG X.R4))] @
	78	(List.concat
	79	(ListPair.map
	80	(fn (num, reg) =>
	81	[X.INSN (X.AL, X.MOVLIT (X.REG X.R4, Word.fromInt (stacksz - 1*(num+1)))),
	82	X.INSN (X.AL, X.ADD (X.REG X.R4, X.REG X.SP)),
	83	X.INSN (X.AL, X.STO (X.REG X.R4, reg))])
	84	(List.tabulate (nsave, fn x => x), savelist)
	85	)
	86	)
6ade8b0a	87	val epilogue =
c2b45b36 JW	88	(List.concat
	89	(ListPair.map
	90	(fn (num, reg) =>
	91	[X.INSN (X.AL, X.MOVLIT (X.REG X.R4, Word.fromInt (stacksz - 1*(num+1)))),
	92	X.INSN (X.AL, X.ADD (X.REG X.R4, X.REG X.SP)),
	93	X.INSN (X.AL, X.LDR (reg, X.REG X.R4))])
	94	(List.tabulate (nsave, fn x => x), savelist)
	95	)
	96	) @
	97	[X.INSN (X.AL, X.MOVLIT (X.REG X.R4, Word.fromInt stacksz)),
	98	X.INSN (X.AL, X.ADD (X.REG X.SP, X.REG X.R4))]
6ade8b0a JW	99	val endlbl = Label.new()
6ade8b0a JW	100
c2b45b36	101	fun spill (X.TEMP temp, xreg: Blarg.reg) = (* Spill a register if need be. *)
5c79bb68	102	let
c2b45b36 JW	103	val base = X.REG X.SP
c2b45b36 JW	104	val offs = Word.fromInt (stackpos (temptonum temp))
5c79bb68	105	in
c2b45b36 JW	106	if (isspilled (X.TEMP temp))
c2b45b36 JW	107	then raise ErrorMsg.InternalError "unspill not supported" ([X.MOV ((X.REL (base, offs, 0w1), Tm.Quad), (X.REG xreg, Tm.Quad))])
5c79bb68 JW	108	else nil
5c79bb68 JW	109	end
c2b45b36	110	\| spill (X.STACKARG _, _) = raise ErrorMsg.InternalError "Cannot spill to a stack arg"
5c79bb68	111	\| spill _ = nil (* Nothing else can be spilled. *)
c2b45b36	112	fun unspill (X.TEMP temp, xreg: Blarg.reg) = (* Unspill a register if need be. *)
5c79bb68	113	let
c2b45b36 JW	114	val base = X.REG X.SP
c2b45b36 JW	115	val offs = Word.fromInt (stackpos (temptonum temp))
5c79bb68	116	in
c2b45b36 JW	117	if (isspilled (X.TEMP temp))
c2b45b36 JW	118	then raise ErrorMsg.InternalError "unspill not supported" ([X.MOV ((X.REG xreg, Tm.Quad), (X.REL (base, offs, 0w1), Tm.Quad))])
5c79bb68 JW	119	else nil
5c79bb68 JW	120	end
c2b45b36	121	\| unspill (X.STACKARG arg, xreg) =
5c79bb68	122	let
c2b45b36 JW	123	val base = X.REG X.SP
c2b45b36 JW	124	val offs = Word.fromInt (stacksz + 8 + (arg * 8))
5c79bb68	125	in
c2b45b36 JW	126	([X.MOV ((X.REG xreg, s), (X.REL (base, offs, 0w1), s))])
c2b45b36 JW	127	raise ErrorMsg.InternalError "unspill from stack not supported"
5c79bb68	128	end
5c79bb68 JW	129	\| unspill _ = nil
5c79bb68 JW	130
c2b45b36 JW	131	fun unspill_ops (op1, op2) =
	132	case (isspilled op1, isspilled op2)
	133	of (false, false) => []
	134	\| (true, false) => unspill (op1, spillreg1)
	135	\| (false, true) => unspill (op2, spillreg2)
	136	\| (true, true) => unspill (op1, spillreg1) @ unspill (op2, spillreg2)
	137
	138	fun respill_ops (op1, op2) =
	139	case (isspilled op1, isspilled op2) (* no instruction writes back to op2 *)
	140	of (false, _) => []
	141	\| (true, _) => spill (op1, spillreg1)
	142
	143	fun real_op1 op1 =
	144	case op1
	145	of (X.TEMP temp) => if isspilled op1
	146	then (X.REG spillreg1)
	147	else X.REG (temptoreg temp)
	148	\| (X.STACKARG arg) => X.REG spillreg1
	149	\| r => r
	150
	151	fun real_ops (op1, op2) =
	152	(case op1
	153	of (X.TEMP temp) => if isspilled op1
	154	then (X.REG spillreg1)
	155	else X.REG (temptoreg temp)
	156	\| (X.STACKARG arg) => X.REG spillreg1
	157	\| r => r,
	158	case op2
	159	of (X.TEMP temp) => if isspilled op2
	160	then (X.REG spillreg2)
	161	else X.REG (temptoreg temp)
	162	\| (X.STACKARG arg) => X.REG spillreg2
	163	\| r => r)
	164
	165	fun whack_insn (pred, insn, op1, op2) =
	166	(map (fn i => X.INSN (pred, i)) (unspill_ops (op1, op2))) @
	167	[ X.INSN (pred, insn (real_ops (op1, op2))) ] @
	168	(map (fn i => X.INSN (pred, i)) (respill_ops (op1, op2)))
1144856b	169
12aa4087 JW	170	fun transform (X.DIRECTIVE s) = [X.DIRECTIVE s]
12aa4087 JW	171	\| transform (X.COMMENT s) = [X.COMMENT s]
c2b45b36	172	\| transform (X.LABEL l) = [X.LABEL l]
6ade8b0a	173	\| transform (X.LIVEIGN a) = transform a
c2b45b36 JW	174
	175	(* god the special cases are going to suck *)
	176	\| transform (X.INSN (pred, X.MOVLIT (op1, w))) =
	177	[ X.INSN (pred, X.MOVLIT (real_op1 op1, w)) ] @
	178	(if isspilled op1
	179	then spill (op1, spillreg1)
	180	else [])
	181	\| transform (X.INSN (pred, X.MOVSYM (op1, w))) =
	182	[ X.INSN (pred, X.MOVSYM (real_op1 op1, w)) ] @
	183	(if isspilled op1
	184	then spill (op1, spillreg1)
	185	else [])
5c90fbb8 JW	186	\| transform (X.INSN (pred, X.MOVSTR (op1, w))) =
	187	[ X.INSN (pred, X.MOVSTR (real_op1 op1, w)) ] @
	188	(if isspilled op1
	189	then spill (op1, spillreg1)
	190	else [])
c2b45b36 JW	191	\| transform (X.INSN (pred, X.MOVLBL (op1, w))) =
	192	[ X.INSN (pred, X.MOVLBL (real_op1 op1, w)) ] @
	193	(if isspilled op1
	194	then spill (op1, spillreg1)
	195	else [])
	196
	197	(* and here comes the boilerplate *)
	198	\| transform (X.INSN (pred, X.LDR (op1, op2))) = whack_insn (pred, X.LDR, op1, op2)
	199	\| transform (X.INSN (pred, X.STO (op1, op2))) = whack_insn (pred, X.STO, op1, op2)
	200	\| transform (X.INSN (pred, X.MOV (op1, op2))) = whack_insn (pred, X.MOV, op1, op2)
	201	\| transform (X.INSN (pred, X.MOVS (op1, op2))) = whack_insn (pred, X.MOVS, op1, op2)
	202	\| transform (X.INSN (pred, X.ADD (op1, op2))) = whack_insn (pred, X.ADD, op1, op2)
	203	\| transform (X.INSN (pred, X.ADDS (op1, op2))) = whack_insn (pred, X.ADDS, op1, op2)
	204	\| transform (X.INSN (pred, X.SUB (op1, op2))) = whack_insn (pred, X.SUB, op1, op2)
	205	\| transform (X.INSN (pred, X.SUBS (op1, op2))) = whack_insn (pred, X.SUBS, op1, op2)
	206	\| transform (X.INSN (pred, X.AND (op1, op2))) = whack_insn (pred, X.AND, op1, op2)
	207	\| transform (X.INSN (pred, X.ANDS (op1, op2))) = whack_insn (pred, X.ANDS, op1, op2)
	208	\| transform (X.INSN (pred, X.NOT (op1, op2))) = whack_insn (pred, X.NOT, op1, op2)
	209	\| transform (X.INSN (pred, X.NOTS (op1, op2))) = whack_insn (pred, X.NOTS, op1, op2)
	210	\| transform (X.INSN (pred, X.PUSH (op1, op2))) = if isspilled op2
	211	then raise ErrorMsg.InternalError "PUSH on spilled op2 is not possible"
	212	else [ X.INSN (pred, X.PUSH (real_ops (op1, op2))) ]
	213	\| transform (X.INSN (pred, X.POP (X.REG X.SP, X.REG X.PC))) = [ X.INSN (pred, X.MOVLBL (X.REG X.PC, endlbl)) ] (* optimize epilogue? *)
	214	\| transform (X.INSN (pred, X.POP (op1, op2))) = if isspilled op2
	215	then raise ErrorMsg.InternalError "POP on spilled op2 is not possible"
	216	else [ X.INSN (pred, X.POP (real_ops (op1, op2))) ]
	217	\| transform (X.INSN (pred, X.CALL (op1, op2, i))) = if isspilled op2
	218	then raise ErrorMsg.InternalError "CALL on spilled op2 is not possible"
	219	else [ X.INSN (pred, X.CALL ((fn (x, y) => (x, y, i)) (real_ops (op1, op2)))) ]
	220	\| transform (X.INSN (pred, X.SHR (op1, op2))) = whack_insn (pred, X.SHR, op1, op2)
	221	\| transform (X.INSN (pred, X.SHL (op1, op2))) = whack_insn (pred, X.SHL, op1, op2)
	222	(\| transform _ = raise ErrorMsg.InternalError "unimplemented")
12aa4087	223	in
c2b45b36	224	(*if (nsave < 2) then
6ade8b0a JW	225	List.concat (prologue :: (map transform instrs))
6ade8b0a JW	226	else
c2b45b36 JW	227	*)
	228	List.concat (prologue ::
	229	((map transform instrs) @
	230	[[X.LABEL endlbl],
	231	epilogue,
	232	[X.INSN (X.AL, X.POP (X.REG X.SP, X.REG X.PC))]
	233	]
	234	)
	235	)
12aa4087 JW	236	end
12aa4087 JW	237	end