X-Git-Url: http://git.joshuawise.com/snipe.git/blobdiff_plain/0a24e44d4e9f82f8d3d83de8e58c83c8cf2868b6..141a7120aec6ddf3ab097f275498d8e3a1b90401:/codegen/codegen.sml diff --git a/codegen/codegen.sml b/codegen/codegen.sml index 9b99ef7..aad1770 100644 --- a/codegen/codegen.sml +++ b/codegen/codegen.sml @@ -1,4 +1,4 @@ -(* L2 Compiler +(* L3 Compiler * Assembly code generator for fake x86 assembly * Author: Joshua Wise * Author: Chris Lu @@ -6,181 +6,315 @@ signature CODEGEN = sig - val codegen : Tree.stm list -> x86.insn list + val codegen : Tree.stm list -> Blarg.insn list end structure Codegen :> CODEGEN = struct structure T = Tree - structure X = x86 + structure TU = TreeUtils + structure X = Blarg + structure Tm = Temp + + (* hasfixed : T.exp -> bool + * true iff the given expression has an hasfixed. + *) + fun hasfixed (T.CALL _) = true + | hasfixed (T.BINOP(_, a, b)) = (hasfixed a) orelse (hasfixed b) + | hasfixed (T.UNOP (_, a)) = hasfixed a + | hasfixed (T.ALLOC(_)) = true + | hasfixed (T.MEMORY (m)) = hasfixed m + | hasfixed (T.STMVAR _) = true + | hasfixed _ = false + + (* binophit : X.oper -> X.opc -> T.exp -> T.exp -> X.insn list *) + (* binophit d oper e1 e2 + * generates instructions to achieve d <- e1 oper e2 + * oper should be something like X.ADD + *) + fun binophit d oper e1 e2 = + let + val t = X.TEMP (Tm.new "binop") + val i1 = munch_exp d e1 + val i2 = munch_exp t e2 +(* val _ = print ("s1 = " ^ Tm.sfx s1 ^ ", s2 = " ^ Tm.sfx s2 ^ ", ") *) +(* val _ = print ("rs = " ^ Tm.sfx rs ^ " from " ^ TU.Print.pp_exp e1 ^ " and " ^ TU.Print.pp_exp e2 ^ "\n") *) + in + i1 @ i2 @ [X.INSN (X.AL, oper (d, t))] + end + + (* cmphit : X.oper -> X.exp -> X.insn list + * cmphit d ex + * generates instructions to set d based on the truth value of ex + *) + and cmphit d ex = + let + val (insns, pos, neg) = munch_cond ex + in + insns @ [X.INSN (X.AL, X.MOVLIT (d, 0w0)), X.INSN (pos, X.MOVLIT (d, 0w1))] + end (* munch_exp : prex86oper -> T.exp -> prex86insn list *) (* munch_exp d e * generates instructions to achieve d <- e * d must be TEMP(t) or REG(r) *) - fun munch_exp d (T.CONST(n)) = [X.MOVL(d, X.CONST n)] - | munch_exp d (T.TEMP(t)) = [X.MOVL(d, X.TEMP t)] - | munch_exp d (T.BINOP(T.ADD, e1, T.CONST n)) = (munch_exp d e1) @ [X.ADDL(d, X.CONST n)] - | munch_exp d (T.BINOP(T.ADD, T.CONST n, e1)) = (munch_exp d e1) @ [X.ADDL(d, X.CONST n)] - | munch_exp d (T.BINOP(T.ADD, e1, e2)) = + and munch_exp d (T.CONST n) = [X.INSN (X.AL, X.MOVLIT(d, Word.fromLarge n))] + | munch_exp d (T.NULLPTR) = [X.INSN (X.AL, X.MOVLIT(d, 0w0))] + | munch_exp d (T.TEMP(t)) = [X.INSN (X.AL, X.MOV(d, X.TEMP t))] + | munch_exp d (T.ARG(0)) = [X.INSN (X.AL, X.MOV(d, X.REG X.R0))] + | munch_exp d (T.ARG(1)) = [X.INSN (X.AL, X.MOV(d, X.REG X.R1))] + | munch_exp d (T.ARG(2)) = [X.INSN (X.AL, X.MOV(d, X.REG X.R2))] + | munch_exp d (T.ARG(3)) = [X.INSN (X.AL, X.MOV(d, X.REG X.R3))] + | munch_exp d (T.ARG(t)) = [X.INSN (X.AL, X.MOV(d, X.STACKARG (t - 4)))] + | munch_exp d (T.CALL(name, l)) = (* Scary demons live here. *) let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ [X.ADDL(d, X.TEMP t1)] - end - | munch_exp d (T.BINOP(T.SUB, T.CONST 0w0, e1)) = (munch_exp d e1) @ [X.NEG d] - | munch_exp d (T.BINOP(T.SUB, e1, T.CONST(n))) = (munch_exp d e1) @ [X.SUBL(d, X.CONST n)] - | munch_exp d (T.BINOP(T.SUB, e1, e2)) = - let val - t1 = Temp.new () + val nargs = length l + val nstack = if (nargs <= 4) + then 0 + else nargs - 4 + val stackb = nstack * 1 + fun argdest 1 = X.REG X.R0 + | argdest 2 = X.REG X.R1 + | argdest 3 = X.REG X.R2 + | argdest 4 = X.REG X.R3 + | argdest n = raise ErrorMsg.InternalError "more than 4 args not supported yet" (*X.REL ((X.REG X.RSP, Tm.Quad), (X.CONST (Word32.fromInt (~(stackb - 8 * (n - 7)))), Tm.Quad), 0w1)*) + + val dests = List.tabulate (nargs, fn x => argdest (x+1)) + val hf = List.map hasfixed l + val (d_hf, l_hf) = ListPair.unzip (ListPair.foldr + (fn (a,b,c) => if b then a::c else c) + nil + (ListPair.zip (dests,l), hf) + ) + val (d_nohf, l_nohf) = ListPair.unzip (ListPair.foldr + (fn (a,b,c) => if b then c else a::c) + nil + (ListPair.zip (dests,l), hf) + ) + val temps = List.map (fn _ => Temp.new ("arg")) l_hf + val argevals_hf = List.map + (fn (t,exp) => munch_exp (X.TEMP t) exp) + (ListPair.zip (temps, l_hf)) + val argpushes = List.map + (fn (dest, t) => [X.INSN (X.AL, X.MOV (dest, X.TEMP t))]) + (ListPair.zip (d_hf, temps)) + val argevals_nohf = List.map + (fn (d,exp) => munch_exp d exp) + (ListPair.zip (d_nohf, l_nohf)) + + val t_stackb = Temp.new ("stackb") + val t_target = Temp.new ("target") in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ [X.SUBL(d, X.TEMP t1)] + List.concat argevals_hf @ + List.concat argpushes @ + List.concat argevals_nohf @ + [ X.INSN (X.AL, X.MOVLIT (X.TEMP t_stackb, Word.fromInt stackb)), + X.INSN (X.AL, X.MOVSYM (X.TEMP t_target, name)), + X.INSN (X.AL, X.SUB (X.REG X.SP, X.TEMP t_stackb)), + X.INSN (X.AL, X.CALL (X.REG X.SP, X.TEMP t_target, nargs)), + X.INSN (X.AL, X.ADD (X.REG X.SP, X.TEMP t_stackb)), + X.INSN (X.AL, X.MOV (d, X.REG X.R0))] end - | munch_exp d (T.BINOP(T.MUL, T.TEMP t, T.CONST n)) = [X.IMUL3(d, X.TEMP t, n)] - | munch_exp d (T.BINOP(T.MUL, T.CONST n, T.TEMP t)) = [X.IMUL3(d, X.TEMP t, n)] - | munch_exp d (T.BINOP(T.MUL, e1, T.CONST n)) = (munch_exp d e1) @ [X.IMUL(d, X.CONST n)] - | munch_exp d (T.BINOP(T.MUL, T.CONST n, e1)) = (munch_exp d e1) @ [X.IMUL(d, X.CONST n)] - | munch_exp d (T.BINOP(T.MUL, e1, e2)) = + (*| munch_exp d (T.BINOP(T.ADD, e1, T.CONST n)) = binophit_c d X.ADD e1 n + | munch_exp d (T.BINOP(T.ADD, T.CONST n, e1)) = binophit_c d X.ADD e1 n + | munch_exp d (T.BINOP(T.ADD, e1, T.TEMP t)) = binophit_t d X.ADD e1 t + | munch_exp d (T.BINOP(T.ADD, T.TEMP t, e1)) = binophit_t d X.ADD e1 t*) + | munch_exp d (T.BINOP(T.ADD, e1, e2)) = binophit d X.ADD e1 e2 + + (*| munch_exp d (T.BINOP(T.SUB, e1, T.CONST n)) = binophit_c d X.SUB e1 n + | munch_exp d (T.BINOP(T.SUB, e1, T.TEMP t)) = binophit_t d X.SUB e1 t*) + | munch_exp d (T.BINOP(T.SUB, e1, e2)) = binophit d X.SUB e1 e2 + | munch_exp d (T.BINOP(T.MUL, _, _)) = raise ErrorMsg.InternalError "MUL does not exist on blargcpu" + | munch_exp d (T.BINOP(T.DIV, _, _)) = raise ErrorMsg.InternalError "DIV does not exist on blargcpu" + | munch_exp d (T.BINOP(T.MOD, _, _)) = raise ErrorMsg.InternalError "MOD does not exist on blargcpu" + | munch_exp d (T.BINOP(T.LSH, e1, e2)) = binophit d X.SHL e1 e2 + | munch_exp d (T.BINOP(T.RSH, e1, e2)) = binophit d X.SHR e1 e2 + | munch_exp d (T.BINOP(T.BITAND, e1, e2)) = binophit d X.AND e1 e2 + | munch_exp d (T.BINOP(T.BITOR, e1, e2)) = munch_exp d (T.UNOP (T.BITNOT, T.BINOP (T.BITAND, T.UNOP (T.BITNOT, e1), T.UNOP (T.BITNOT, e2)))) + | munch_exp d (T.BINOP(T.BITXOR, e1, e2)) = + munch_exp d (T.BINOP(T.BITOR, T.BINOP(T.BITAND, e1, T.UNOP(T.BITNOT, e2)), + T.BINOP(T.BITAND, e2, T.UNOP(T.BITNOT, e1)))) + + | munch_exp d (a as T.BINOP(T.LOGAND, e1, e2)) = let - val t1 = Temp.new () + val (insn1, pos1, neg1) = munch_cond e1 + val (insn2, pos2, neg2) = munch_cond e2 + val l = Label.new () in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ [X.IMUL(d, X.TEMP t1)] + (insn1) @ + [X.INSN (X.AL, X.MOVLIT (d, 0w0)), + X.INSN (neg1, X.MOVLBL (X.REG X.PC, l))] @ + (insn2) @ + [X.INSN (pos2, X.MOVLIT (d, 0w1)), + X.LABEL l] end - | munch_exp d (T.BINOP(T.DIV, e1, e2)) = + | munch_exp d (a as T.BINOP(T.LOGOR, e1, e2)) = let - val t1 = Temp.new () + val (insn1, pos1, neg1) = munch_cond e1 + val (insn2, pos2, neg2) = munch_cond e2 + val t1 = X.TEMP (Tm.new "logand 1") + val t2 = X.TEMP (Tm.new "logand 2") + val l = Label.new () in - (munch_exp (X.TEMP t1) e1) @ (munch_exp d e2) @ - [X.MOVL (X.REG X.EAX, X.TEMP t1), X.CLTD, X.IDIVL d, X.MOVL (d, X.REG X.EAX)] + (insn1) @ + [X.INSN (X.AL, X.MOVLIT (d, 0w0)), + X.INSN (pos1, X.MOVLIT (d, 0w1)), + X.INSN (pos1, X.MOVLBL (X.REG X.PC, l))] @ + (insn2) @ + [X.INSN (pos2, X.MOVLIT (d, 0w1)), + X.LABEL l] end - | munch_exp d (T.BINOP(T.MOD, e1, e2)) = + | munch_exp d (a as T.BINOP(T.EQ, _, _)) = cmphit d a + | munch_exp d (a as T.BINOP(T.NEQ, _, _)) = cmphit d a + | munch_exp d (a as T.BINOP(T.LE, _, _)) = cmphit d a + | munch_exp d (a as T.BINOP(T.LT, _, _)) = cmphit d a + | munch_exp d (a as T.BINOP(T.GE, _, _)) = cmphit d a + | munch_exp d (a as T.BINOP(T.GT, _, _)) = cmphit d a + | munch_exp d (a as T.BINOP(T.BE, _, _)) = cmphit d a + + | munch_exp d (T.UNOP(T.NEG, e1)) = let - val t1 = Temp.new () + val t = Temp.new "-val" + val i = munch_exp (X.TEMP t) e1 in - (munch_exp (X.TEMP t1) e1) @ (munch_exp d e2) @ - [X.MOVL (X.REG X.EAX, X.TEMP t1), X.CLTD, X.IDIVL d, X.MOVL (d, X.REG X.EDX)] + (i) @ + [X.INSN (X.AL, X.MOVLIT (d, 0w0)), + X.INSN (X.AL, X.SUB (d, X.TEMP t))] end - | munch_exp d (T.BINOP(T.LSH, e1, T.CONST n)) = (munch_exp d e1) @ [X.SALL (d, X.CONST n)] - | munch_exp d (T.BINOP(T.LSH, e1, e2)) = + | munch_exp d (T.UNOP(T.BITNOT, e1)) = let val i = munch_exp d e1 in i @ [X.INSN (X.AL, X.NOT (d, d))] end + | munch_exp d (T.UNOP(T.BANG, e)) = let - val t1 = Temp.new() + val (insns, pos, neg) = munch_cond e in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ - [X.MOVL (X.REG X.ECX, X.TEMP t1), X.SALL (d, X.REG X.ECX)] + insns @ + [X.INSN (X.AL, X.MOVLIT (d, 0w0)), + X.INSN (neg, X.MOVLIT (d, 0w1))] end - | munch_exp d (T.BINOP(T.RSH, e1, T.CONST n)) = (munch_exp d e1) @ [X.SARL (d, X.CONST n)] - | munch_exp d (T.BINOP(T.RSH, e1, e2)) = + | munch_exp d (T.MEMORY (e1)) = let - val t1 = Temp.new() + val a = X.TEMP (Temp.new "addr") + val i = munch_exp a e1 in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ - [X.MOVL (X.REG X.ECX, X.TEMP t1), X.SARL (d, X.REG X.ECX)] + i @ + [X.INSN (X.AL, X.LDR (d, a))] end - | munch_exp d (T.BINOP(T.LOGOR, e1, e2)) = + + | munch_exp d (T.ALLOC(exp)) = let + val t1 = Temp.new "alloc" val l1 = Label.new() + val einsn = munch_exp (X.TEMP t1) exp + val insns = munch_exp d (T.CALL (Symbol.symbol "calloc", [T.TEMP t1, T.CONST 0w1])) in - (munch_exp d e1) @ [X.CMPL (d, X.CONST(0w0)), X.JNE l1] @ (munch_exp d e2) @ [X.CMPL (d, X.CONST(0w0)), X.LABEL l1, X.SETNE d, X.MOVZBL(d,d)] + einsn @ insns end - | munch_exp d (T.BINOP(T.LOGAND, e1, e2)) = +(* | munch_exp d (T.COND(c, T.CONST n1, T.CONST n2)) = let val (i,p,n) = munch_cond c in ((X.MOV (d, X.CONST n1))::i) @ [X.CMOVcc (p, d, X.CONST n2)] end *) + | munch_exp d (T.COND(c,e1,e2)) = let + val (insns, pos, neg) = munch_cond c val l1 = Label.new() + val l2 = Label.new() + val i1 = munch_exp d e1 + val i2 = munch_exp d e2 +(* val _ = print ("cond: size " ^ Tm.sfx s1 ^ " from " ^ TU.Print.pp_exp e1 ^ ", " ^ Tm.sfx s2 ^ " from " ^ TU.Print.pp_exp e2 ^ "\n") *) in - (munch_exp d e1) @ [X.CMPL (d, X.CONST(0w0)), X.JE l1] @ (munch_exp d e2) @ [X.CMPL (d, X.CONST(0w0)), X.LABEL l1, X.SETNE d, X.MOVZBL(d,d)] + insns @ + [X.INSN (neg, X.MOVLBL (X.REG X.PC, l1))] @ + i1 @ + [X.INSN (X.AL, X.MOVLBL (X.REG X.PC, l2)), + X.LABEL l1] @ + i2 @ + [X.LABEL l2] end - | munch_exp d (T.BINOP(T.BITAND, e1, e2)) = - let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ [X.ANDL(d, X.TEMP t1)] - end - | munch_exp d (T.BINOP(T.BITOR, e1, e2)) = - let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ [X.ORL(d, X.TEMP t1)] - end - | munch_exp d (T.BINOP(T.BITXOR, e1, e2)) = - let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ [X.XORL(d, X.TEMP t1)] - end - | munch_exp d (T.BINOP(T.NEQ, e1, e2)) = - let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ - [X.CMPL(d, X.TEMP t1), X.SETNE(d), X.MOVZBL(d, d)] - end - | munch_exp d (T.BINOP(T.EQ, e1, e2)) = - let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ - [X.CMPL(d, X.TEMP t1), X.SETE(d), X.MOVZBL(d, d)] - end - | munch_exp d (T.BINOP(T.LE, e1, e2)) = - let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ - [X.CMPL(d, X.TEMP t1), X.SETLE(d), X.MOVZBL(d, d)] - end - | munch_exp d (T.BINOP(T.LT, e1, e2)) = - let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ - [X.CMPL(d, X.TEMP t1), X.SETL(d), X.MOVZBL(d, d)] - end - | munch_exp d (T.BINOP(T.GE, e1, e2)) = - let - val t1 = Temp.new () - in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ - [X.CMPL(d, X.TEMP t1), X.SETGE(d), X.MOVZBL(d, d)] - end - | munch_exp d (T.BINOP(T.GT, e1, e2)) = + | munch_exp d (T.STMVAR (sl, e)) = let val i = munch_exp d e in List.concat (map munch_stm sl) @ i end + + and condhit e1 e2 (pos, neg) = + let + val t1 = X.TEMP (Temp.new ("var neq 1")) + val t2 = X.TEMP (Temp.new ("var neq 2")) + val i1 = munch_exp t1 e1 + val i2 = munch_exp t2 e2 + in + (i1 @ i2 @ [X.INSN (X.AL, X.SUBS (t1, t2))], pos, neg) + end + + (* munch_cond : T.exp -> X.insn list * X.cond * X.cond + * munch_cond stm generates code to set flags, and then returns a conditional + * to test if the expression was true and for if it was false. + *) + and munch_cond (T.UNOP (T.BANG, e)) = let - val t1 = Temp.new () + val (insns, pos, neg) = munch_cond e in - (munch_exp d e1) @ (munch_exp (X.TEMP t1) e2) @ - [X.CMPL(d, X.TEMP t1), X.SETG(d), X.MOVZBL(d, d)] + (insns, neg, pos) end - | munch_exp d (T.UNOP(T.NEG, e1)) = (munch_exp d e1) @ [X.NEG d] - | munch_exp d (T.UNOP(T.BITNOT, e1)) = (munch_exp d e1) @ [X.NOTL d] - | munch_exp d (T.UNOP(T.BANG, e1)) = (munch_exp d e1) @ - [X.TEST(d,d), X.SETE(d), X.MOVZBL(d, d)] + | munch_cond (T.BINOP(T.NEQ, e1, e2)) = condhit e1 e2 (X.NE, X.EQ) + | munch_cond (T.BINOP(T.EQ, e1, e2)) = condhit e1 e2 (X.EQ, X.NE) + | munch_cond (T.BINOP(T.LE, e1, e2)) = condhit e1 e2 (X.LE, X.GT) + | munch_cond (T.BINOP(T.LT, e1, e2)) = condhit e1 e2 (X.LT, X.GE) + | munch_cond (T.BINOP(T.GT, e1, e2)) = condhit e1 e2 (X.GT, X.LE) + | munch_cond (T.BINOP(T.GE, e1, e2)) = condhit e1 e2 (X.GE, X.LT) + + | munch_cond (T.BINOP(T.BE, e1, e2)) = raise ErrorMsg.InternalError "memory safety not supported" + + | munch_cond e = + let + val t = X.TEMP (Temp.new ("munch c")) + val i = munch_exp t e + in + (i @ [ X.INSN (X.AL, X.MOVS (t,t)) ], X.NE, X.EQ) + end + + (* munch_lval : T.exp -> X.operand + * Takes an expression that has been typechecked as being a valid lvalue and a location of a datum, and then returns an instruction list to store. + *) + and munch_lval (T.TEMP t) oper = [X.INSN (X.AL, X.MOV (oper, X.TEMP t))] + | munch_lval (T.MEMORY m) oper = + let + val t = X.TEMP (Tm.new "lv addr") + val i = munch_exp t m + in + i @ + [X.INSN (X.AL, X.STO (t, oper))] + end + | munch_lval _ _ = raise ErrorMsg.InternalError "That wasn't really a valid lvalue..." (* munch_stm : T.stm -> X.insn list *) (* munch_stm stm generates code to execute stm *) - fun munch_stm (T.MOVE(T.TEMP(t1), e2)) = + and munch_stm (T.MOVE (T.TEMP t1, T.TEMP t2)) = [X.INSN (X.AL, X.MOV(X.TEMP t1, X.TEMP t2))] + | munch_stm (T.MOVE (T.TEMP t, T.CONST n)) = [X.INSN (X.AL, X.MOVLIT(X.TEMP t, Word.fromLarge n))] + | munch_stm (T.MOVE (T.TEMP t, a as T.ARG (an))) = + let + val i = munch_exp (X.TEMP t) a + in + i + end + | munch_stm (T.MOVE (T.TEMP t, a as T.CALL _)) = munch_exp (X.TEMP t) a + | munch_stm (T.MOVE (a, e2)) = let - val t = Temp.new () + val t = X.TEMP (Temp.new ("assign")) + val i = munch_exp t e2 + val li = munch_lval a t in - munch_exp (X.TEMP t) e2 - @ [X.MOVL(X.TEMP t1, X.TEMP t)] + i @ li end - | munch_stm (T.MOVE(_, _)) = - raise ErrorMsg.InternalError "Incorrect first operand for T.MOVE?" | munch_stm (T.RETURN(e)) = let - val t = Temp.new () + val t = X.TEMP (Temp.new ("retval")) + val i = munch_exp t e in - munch_exp (X.TEMP t) e - @ [X.MOVL(X.REG X.EAX, X.TEMP t), X.RET] + i @ [X.INSN (X.AL, X.MOV(X.REG X.R0, t)), X.INSN (X.AL, X.POP (X.REG X.SP, X.REG X.PC))] end - | munch_stm (T.LABEL(l)) = [X.LABEL l] - | munch_stm (T.JUMP(l)) = [X.JMP l] + | munch_stm (T.LABEL l) = [X.LABEL l] + | munch_stm (T.JUMP l) = [X.INSN (X.AL, X.MOVLBL (X.REG X.PC, l))] | munch_stm (T.JUMPIFN(e, l)) = let - val t = Temp.new () + val (insns, pos, neg) = munch_cond e in - munch_exp (X.TEMP t) e - @ [X.TEST(X.TEMP t, X.TEMP t), X.JE l] + insns @ [X.INSN (neg, X.MOVLBL (X.REG X.PC, l))] end + | munch_stm (T.EFFECT exp) = let val t = X.TEMP (Temp.new "throwaway") val i = munch_exp t exp in i end fun codegen nil = nil | codegen (stm::stms) = munch_stm stm @ codegen stms