synth/tools/cc.py

import argparse
import collections
import contextlib
import importlib
import io
import re
import subprocess
import sys

import lark

asmod = importlib.import_module("as")

GRAMMAR_FILE = '/home/paulmathieu/vhdl/tools/cc.ebnf'
CPP = ('cpp', '-P')


class Scope:
    def __init__(self):
        self.symbols = {}
        self.parent = None


class Variable:
    def __init__(self, type, name, volatile=False, addr_reg=None):
        self.type = type
        self.name = name
        self.volatile = volatile
        self.addr_reg = addr_reg

    def __repr__(self):
        return f'<Var: {self.type} {self.name}>'

    @classmethod
    def from_def(cls, tree):
        volatile = False
        type = tree.children[0]
        if isinstance(type, lark.Tree):
            for c in type.children:
                if c == "volatile":
                    volatile = True
        name = tree.children[1]
        return cls(type, name, volatile=volatile)

    @classmethod
    def from_dereference(cls, reg):
        return cls('deref', 'deref', addr_reg=reg)


# - all registers pointing to unwritten stuff can be dropped as soon as we're
#   done with them:
#   - already fed them into the operations
#   - end of statement
# - maybe should have a separate storeage for special registers?
# need ways to:
# - assign a list of registers into r0, ... rn for function call
#   - ... and run all callbacks
# - get the register for an identifier
# - dereference an expression:
#   - essentially turn a temp into an lvalue-address
#     - if read, need a second reg for its value
#   - mark a variable to have its address in a register
# - delay reading the identifier if it's lhs
# - store the value to memory when registers are claimed
#   - if it was modified through:
#       - assignment
#       - pre-post *crement
#   - retrieve the memory type:
#     - stack
#     - absolute
#     - register
# - or just store the value when the variable is assigned
# - get a temporary register
# - return it
# - I guess dereferencing is an upgrade

    def type(self, tree):
        print(tree)


class RegBank:
    def __init__(self, logger=None):
        self.reset()
        self.log = logger or print

    def reset(self):
        self.available = [f'r{i}' for i in range(12)]
        self.vars = {}
        self.varregs = {}
        self.cleanup = collections.defaultdict(list)

    def take(self, reg=None):
        if reg is not None:
            if reg not in self.available:
                self.evict(self.var(reg))
            self.available.remove(reg)
            return reg
        if not self.available:
            assert self.vars, "nothing to clean, no more regs :/"
            # storing one random var
            var = list(self.vars.keys())[0]
            self.evict(var)
        return self.available.pop(0)

    def give(self, reg):
        if reg in self.varregs:
            # Need to call evict() with the var to free it.
            return
        self.available.insert(0, reg)

    def loaded(self, var, reg, cleanup=None):
        """Tells the regbank some variable was loaded into the given register."""
        self.vars[var] = reg
        self.varregs[reg] = var
        self.take(reg)
        if cleanup is not None:
            self.log(f'recording cleanup for {reg}({var.name})')
            self.cleanup[reg].append(cleanup)

    def stored(self, var):
        """Tells the regbank the given var was stored to memory, register can be freed."""
        assert var in self.vars
        reg = self.vars.pop(var)
        del self.varregs[reg]
        self.give(reg)

    def load(self, var):
        """Returns the reg associated with the var, or a new reg if none was,
        and True if the var was created, False otherwise."""
        self.log(f'vars: {self.vars}, varregs: {self.varregs}')
        if var not in self.vars:
            reg = self.take()
            self.vars[var] = reg
            self.varregs[reg] = var
            return reg, True
        return self.vars[var], False

    def assign(self, var, reg, cleanup=None):
        """Assign a previously-used register to a variable."""
        if var in self.vars:
            self.stored(var)
        if reg in self.varregs:
            for cb in self.cleanup.pop(reg, []):
                cb(reg)
            self.stored(self.varregs[reg])
        self.vars[var] = reg
        self.varregs[reg] = var
        if cleanup is not None:
            self.cleanup[reg].append(cleanup)

    def var(self, reg):
        return self.varregs.get(reg, None)

    def evict(self, var):
        """Runs var callbacks & frees the register."""
        if var not in self.vars:
            return
        reg = self.vars[var]
        for cb in self.cleanup.pop(var, []):
            cb(reg)
        self.stored(var)

    def flush_all(self):
        for reg in list(self.cleanup):
            self.log(f'flushing {reg}({self.varregs[reg].name})')
            for cb in self.cleanup.pop(reg):
                cb(reg)
        self.reset()

    def swapped(self, reg0, reg1):
        var0 = self.varregs.get(reg0, None)
        var1 = self.varregs.get(reg1, None)

        if var0 is not None:
            self.stored(var0)
        elif reg0 not in self.available:
            self.give(reg0)

        if var1 is not None:
            self.stored(var1)
        elif reg1 not in self.available:
            self.give(reg1)

        if var0 is not None:
            self.loaded(var0, reg1)
        if var1 is not None:
            self.loaded(var1, reg0)

    def snap(self):
        return dict(self.vars), dict(self.cleanup)

    def restore(self, snap):
        self.reset()
        vardict, cleanup = snap
        for var, reg in vardict.items():
            self.loaded(var, reg, cleanup=cleanup.get(reg, None))

    @contextlib.contextmanager
    def borrow(self, howmany):
        regs = [self.take() for i in range(howmany)]
        yield regs
        for reg in regs:
            self.give(reg)


class FunctionSpec:
    def __init__(self, fun_prot):
        self.return_type = fun_prot.children[0]
        self.name = fun_prot.children[1]
        self.param_types = [x.children[0] for x in fun_prot.children[2:]]

    def __repr__(self):
        params = ', '.join(self.param_types)
        return f'<Function: {self.return_type} {self.name}({params})>'


class Function:
    def __init__(self, fun_prot):
        self.locals = {}
        self.spec = FunctionSpec(fun_prot)
        self.params = [Variable(*x.children) for x in fun_prot.children[2:]]
        self.ret = None
        self.nextstack = 0
        self.statements = []
        self.regs = RegBank(logger=self.log)
        self.deferred_ops = []
        self.fun_calls = 0
        self.ops = []

    def log(self, line):
        self.ops.append(lambda: [f'// {line}'])

    @property
    def stack_usage(self):
        return self.nextstack + 2

    def get_stack(self, size=2):
        stk = self.nextstack
        self.nextstack += size
        return stk

    def param_dict(self):
        return {p.name: p for p in self.params}

    def __repr__(self):
        return repr(self.spec)

    def synth(self):
        if self.fun_calls > 0:
            preamble = [f'store lr, [sp, -2]',
                        f'set r4, {self.stack_usage}',
                        f'sub sp, sp, r4']
        else:
            preamble = []

        ops = preamble
        for op in self.ops:
            ops += op()
        indented = [f' {x}' if x[-1] == ':' else f'  {x}' for x in ops]
        return [f'.global {self.spec.name}',
                f'{self.spec.name}:'] + indented


class CcTransform(lark.visitors.Transformer):
    def _binary_op(litt):
        @lark.v_args(tree=True)
        def _f(self, tree):
            left, right = tree.children
            if left.data == 'litteral' and right.data == 'litteral':
                tree.data = 'litteral'
                tree.children = [litt(left.children[0], right.children[0])]
            return tree
        return _f

    def array_item(self, children):
        # transform blarg[foo] into *(blarg + foo) because reasons
        addop = lark.Tree('add', children)
        return lark.Tree('dereference', [addop])

    # operations on litterals can be done by the compiler
    add = _binary_op(lambda a, b: a+b)
    sub = _binary_op(lambda a, b: a-b)
    mul = _binary_op(lambda a, b: a*b)
    shl = _binary_op(lambda a, b: a<<b)

    CHARACTER = lambda _, x: ord(x[1])
    IDENTIFIER = str
    SIGNED_NUMBER = int
    HEX_LITTERAL = lambda _, x: int(x[2:], 16)


class AsmOp:
    scratch_need = 0

    def synth(self, scratches):
        return [f'nop']

    @property
    def out(self):
        return None


class Reg:
    scratch_need = 0

    def __init__(self, reg):
        self.out = reg

    def synth(self, scratches):
        return []


class BinOp(AsmOp):
    scratch_need = 0

    def __init__(self, fun, ops):
        self.fun = fun
        self.dest, self.left, self.right = ops

    @property
    def out(self):
        return self.dest


def make_cpu_bin_op(cpu_op):
    class _C(BinOp):
        def synth(self, _):
            return [f'{cpu_op} {self.dest}, {self.left}, {self.right}']
    return _C


AddOp = make_cpu_bin_op('add')
SubOp = make_cpu_bin_op('sub')
MulOp = make_cpu_bin_op('mul')
# no div
# no mod either
AndOp = make_cpu_bin_op('and')
orOp = make_cpu_bin_op('or')
XorOp = make_cpu_bin_op('xor')

class ShlOp(BinOp):
    scratch_need = 2
    def synth(self, scratches):
        sc0, sc1 = scratches
        return [f'set {sc1}, 1',
                f'or {self.dest}, {self.left}, {self.left}',
                f'sub {sc0}, {self.right}, {sc1}',
                f'beq [pc, 6]',
                f'add {self.dest}, {self.dest}, {self.dest}',
                f'sub {sc0}, {sc0}, {sc1}',
                f'bneq [pc, -6]']


class LtOp(BinOp):
    scratch_need = 1
    def synth(self, scratches):
        sc0 = scratches[0]
        return [f'set {self.dest}, 0',
                f'sub {sc0}, {self.left}, {self.right}',
                f'bneq [pc, 2]',
                f'set {self.dest}, 1']

class GtOp(LtOp):
    def __init__(self, fun, ops):
        dest, left, right = ops
        super(GtOp, self).__init__(fun, [dest, right, left])


class UnOp(AsmOp):
    scratch_need = 0

    def __init__(self, fun, ops):
        self.fun = fun
        self.dest, self.operand = ops

    @property
    def out(self):
        return self.dest


class Incr(UnOp):
    scratch_need = 1
    def synth(self, scratches):
        sc0 = scratches[0]
        return [f'set {sc0}, 1',
                f'add {self.dest}, {self.operand}, {sc0}',
                f'or {self.operand}, {self.dest}, {self.dest}']

class Decr(UnOp):
    scratch_need = 1
    def synth(self, scratches):
        sc0 = scratches[0]
        return [f'set {sc0}, 1',
                f'sub {self.dest}, {self.operand}, {sc0}',
                f'or {self.operand}, {self.dest}, {self.dest}']


class NotOp(UnOp):
    def synth(self, scratches):
        return [f'not {self.dest}, {self.operand}']

class BoolNot(UnOp):
    def synth(self, scratches):
        return [f'set {self.dest}, 0',
                f'cmp {self.dest}, {self.operand}',
                f'bneq [pc, 2]',
                f'set {self.dest}, 1']

class NeqOp(BinOp):
    def synth(self, scratches):
        return [f'sub {self.dest}, {self.left}, {self.right}']


class FnCall(AsmOp):
    scratch_need = 1

    def __init__(self, fun, ops):
        self.fun = fun
        self.dest_fn, self.params = ops

    @property
    def out(self):
        return 'r0'

    def synth(self, scratches):
        out = []
        sc0 = scratches[0]
        fn = self.dest_fn

        return out + [f'set {sc0}, 2',
                f'add lr, pc, {sc0}',
                f'or pc, {fn}, {fn}']


class ReturnReg(AsmOp):
    scratch_need = 1

    def __init__(self, fun, ops):
        self.fun = fun
        (self.ret_reg,) = ops

    def synth(self, scratches):
        if self.fun.fun_calls == 0:
            return [f'or r0, {self.ret_reg}, {self.ret_reg}',
                    f'or pc, lr, lr']
        sc0 = scratches[0]
        stack_usage = self.fun.stack_usage
        ret = self.ret_reg
        assert stack_usage < 255
        return [f'set {sc0}, {stack_usage}',
                f'add sp, sp, {sc0}',
                f'or r0, {ret}, {ret}',
                f'load pc, [sp, -2]  // return']


class Load(AsmOp):
    scratch_need = 0

    def __init__(self, fun, ops):
        self.fun = fun
        self.dest, self.var = ops

    @property
    def out(self):
        return self.dest

    def synth(self, scratches):
        reg = self.dest
        if self.var.name in self.fun.locals:
            src = self.var.stackaddr
            return [f'load {reg}, [sp, {src}]']
        elif self.var.addr_reg is not None:
            return [f'load {reg}, [{self.var.addr_reg}]']
        else:
            return [f'set {reg}, {self.var.name}',
                    f'nop  // in case we load a far global',
                    f'load {reg}, [{reg}]']

class Store(AsmOp):
    scratch_need = 1

    def __init__(self, fun, ops):
        self.fun = fun
        self.src, self.var = ops

    @property
    def out(self):
        return None

    def synth(self, scratches):
        (sc,) = scratches
        reg = self.src
        if self.var.name in self.fun.locals:
            dst = self.var.stackaddr
            self.fun.log(f'storing {self.var}({reg}) to [sp, {dst}]')
            return [f'store {reg}, [sp, {dst}]']
        elif self.var.addr_reg is not None:
            return [f'store {reg}, [{self.var.addr_reg}]']
        return [f'set {sc}, {self.var.name}',
                f'nop  // you know, in case blah',
                f'store {reg}, [{sc}]']


class Assign(AsmOp):
    scratch_need = 0

    def __init__(self, fun, ops):
        self.fun = fun
        self.src, self.var = ops

    @property
    def out(self):
        return self.var

    def synth(self, scratches):
        return [f'or {self.var}, {self.src}, {self.src}']


class SetAddr(AsmOp):
    scratch_need = 0

    def __init__(self, fun, ops):
        self.dest, self.ident = ops

    @property
    def out(self):
        return self.dest

    def synth(self, scratches):
        reg = self.dest
        return [f'set {reg}, {self.ident}',
                f'nop  // placeholder for a long address']


class Set16Imm(AsmOp):
    scratch_need = 0

    def __init__(self, fun, ops):
        self.dest, self.imm16 = ops

    @property
    def out(self):
        return self.dest

    def synth(self, scratches):
        reg = self.dest
        hi = (self.imm16 >> 8) & 0xff
        lo = (self.imm16 >> 0) & 0xff
        if hi != 0:
            return [f'set {reg}, {lo}',
                    f'seth {reg}, {hi}']
        else:
            return [f'set {reg}, {lo}']

class Swap(AsmOp):
    scratch_need = 1

    def __init__(self, a0, a1):
        self.a0 = a0
        self.a1 = a1

    def synth(self, scratches):
        (sc0,) = scratches
        return [f'or {sc0}, {self.a0}, {self.a0}',
                f'or {self.a0}, {self.a1}, {self.a1}',
                f'or {self.a1}, {sc0}, {sc0}']


class IfOp(AsmOp):
    scratch_need = 1

    def __init__(self, fun, op):
        self.fun = fun
        self.cond, mark, self.has_else = op

        self.then_mark = f'_then_{mark}'
        self.else_mark = f'_else_{mark}'
        self.endif_mark = f'_endif_{mark}'

    def synth(self, scratches):
        sc0 = scratches[0]
        if self.has_else:
            return [f'set {sc0}, 0',
                    f'cmp {sc0}, {self.cond}',  # flag if cond == 0
                    f'beq {self.else_mark}']
        else:
            return [f'set {sc0}, 0',
                    f'cmp {sc0}, {self.cond}',
                    f'beq {self.endif_mark}']

    def synth_else(self):
        return [f'cmp r0, r0',  # trick because beq is better than "or pc, ."
                f'beq {self.endif_mark}',
                f'{self.else_mark}:']

    def synth_endif(self):
        return [f'{self.endif_mark}:']


class WhileOp(AsmOp):
    scratch_need = 1

    @staticmethod
    def synth_loop(mark):
        loop_mark = f'_loop_{mark}'
        return [f'{loop_mark}:']

    def __init__(self, cond, mark):
        self.cond = cond
        self.loop_mark = f'_loop_{mark}'
        self.endwhile_mark  = f'_endwhile_{mark}'

    def synth(self, scratches):
        sc0 = scratches[0]
        return [f'set {sc0}, 0',
                f'cmp {sc0}, {self.cond}',
                f'beq {self.endwhile_mark}']

    def synth_endwhile(self):
        return [f'cmp r0, r0',
                f'beq {self.loop_mark}',
                f'{self.endwhile_mark}:']


class Delayed(AsmOp):
    def __init__(self, out_cb):
        self.out_cb = out_cb

    @property
    def out(self):
        return self.out_cb()

    def synth(self):
        return []


class CcInterp(lark.visitors.Interpreter):
    def __init__(self):
        self.global_scope = Scope()
        self.cur_scope = self.global_scope
        self.cur_fun = None
        self.funs = []
        self.next_reg = 0
        self.next_marker = 0

    def _lookup_symbol(self, s):
        scope = self.cur_scope
        while scope is not None:
            if s in scope.symbols:
                return scope.symbols[s]
            scope = scope.parent
        return None

    def _get_reg(self):
        return self.cur_fun.regs.take()

    def _get_marker(self):
        mark = self.next_marker
        self.next_marker += 1
        return mark

    def _synth(self, op):
        with self.cur_fun.regs.borrow(op.scratch_need) as scratches:
            self._log(f'{op.__class__.__name__}')
            self.cur_fun.ops.append(lambda: op.synth(scratches))

    def _load(self, ident):
        s = self._lookup_symbol(ident)
        assert s is not None, f'unknown identifier {ident}'
        if isinstance(s, FunctionSpec) or s in self.global_scope.symbols:
            reg = self._get_reg()
            return SetAddr(self.cur_fun, [reg, ident])
        else:
            if s.volatile:
                self._log(f'loading volatile {s}')
                return Load(self.cur_fun, [reg, s])
            reg, created = self.cur_fun.regs.load(s)
            if created:
                return Load(self.cur_fun, [reg, s])
            else:
                self._log(f'{s} was already in {reg}')
                return Reg(reg)

    def identifier(self, tree):
        # TODO: not actually load the value until it's used in an expression
        # could have the op.out() function have a side effect that does that
        # if it's an assignment, we need to make a Variable with the proper
        # address and assign the register to it.
        # If it's volatile, we need to flush it.
        def delayed_load():
            self._log(f'delay-loading {tree.children[0]}')
            op = self._load(tree.children[0])
            self._synth(op)
            return op.out

        tree.op = Delayed(delayed_load)
        tree.var = self._lookup_symbol(tree.children[0])

    def litteral(self, tree):
        imm = tree.children[0]
        reg = self._get_reg()
        assert self.cur_fun is not None
        tree.op = Set16Imm(self.cur_fun, [reg, imm])
        self._synth(tree.op)

    def _assign(self, left, right):
        # need to make sure there's a variable and either:
        # - to store it, or
        # - to mark a register for it
        if left.volatile:
            self._synth(Store(self.cur_fun, [right, left]))
            self.cur_fun.stored(left)
            return
        self._log(f'assigning {left} = {right}')
#        cleanup = lambda reg: self._synth(Store(self.cur_fun, [reg, left]))
        self.cur_fun.regs.assign(left, right)
        self._synth(Store(self.cur_fun, [right, left]))

    def assignment(self, tree):
        self.visit_children(tree)
        val = tree.children[1].op.out

        # left hand side is an lvalue, retrieve it
        var = tree.children[0].var
        self._assign(var, val)

    def global_var(self, tree):
        self.visit_children(tree)
        var = Variable.from_def(tree)
        self.global_scope.symbols[var.name] = var
        val = 0
        if len(tree.children) > 2:
            val = tree.children[2].children[0].value

    def fun_decl(self, tree):
        fun = FunctionSpec(tree.children[0])
        self.cur_scope.symbols[fun.name] = fun

    def _prep_fun_call(self, fn_reg, params):
        """Move all params to r0-rn."""
        def swap(old, new):
            if old == new:
                return
            oldpos = params.index(old)
            try:
                newpos = params.index(new)
            except ValueError:
                params[oldpos] = new
            else:
                params[newpos], params[oldpos] = params[oldpos], params[newpos]
            self._synth(Swap(old, new))

        if fn_reg in [f'r{i}' for i in range(len(params))]:
            new_fn = f'r{len(params)}'
            self._synth(Swap(fn_reg, new_fn))
            fn_reg = new_fn
        for i, param in enumerate(params):
            new = f'r{i}'
            swap(param, new)
        return fn_reg

    def fun_call(self, tree):
        self.cur_fun.fun_calls += 1
        self.visit_children(tree)
        fn_reg = tree.children[0].op.out
        param_regs = [c.op.out for c in tree.children[1:]]
        self.cur_fun.regs.flush_all()
        for i in range(len(param_regs)):
            self.cur_fun.regs.take(f'r{i}')
        fn_reg = self._prep_fun_call(fn_reg, param_regs)
        self.cur_fun.regs.take(fn_reg)
        tree.op = FnCall(self.cur_fun, [fn_reg, param_regs])
        self._synth(tree.op)
        self.cur_fun.regs.reset()
        self.cur_fun.regs.take('r0')

    def statement(self, tree):
        self.visit_children(tree)
        if self.cur_fun.deferred_ops:
            self._log(f'deferred logic: {len(self.cur_fun.deferred_ops)}')
        for op in self.cur_fun.deferred_ops:
            self._synth(op)
        self.cur_fun.deferred_ops = []

    iter_expression = statement

    def if_stat(self, tree):
        self.visit(tree.children[0])
        mark = self._get_marker()
        has_else = len(tree.children) > 2
        op = IfOp(self.cur_fun, [tree.children[0].op.out, mark, has_else])
        self._synth(op)
        begin_vars = self.cur_fun.regs.snap()
        self.visit(tree.children[1])
        if has_else:
            self.cur_fun.regs.restore(begin_vars)
            self.cur_fun.ops.append(op.synth_else)
            self.visit(tree.children[2])
        self.cur_fun.ops.append(op.synth_endif)

    def while_stat(self, tree):
        mark = self._get_marker()
        self.cur_fun.ops.append(lambda: WhileOp.synth_loop(mark))
        begin_vars = dict(self.cur_fun.regs.vars)
        self.visit(tree.children[0])
        op = WhileOp(tree.children[0].op.out, mark)
        self._synth(op)
        self.visit(tree.children[1])
        for v, r in begin_vars.items():
            rvars = self.cur_fun.regs.vars
            if v not in rvars or rvars[v] != r:
                self._log(f'loading missing var {v}')
                self._synth(Load(self.cur_fun, [r, v]))
        self.cur_fun.ops.append(op.synth_endwhile)

    def for_stat(self, tree):
        mark = self._get_marker()
        self.visit(tree.children[0])  # initialization
        self.cur_fun.ops.append(lambda: WhileOp.synth_loop(mark))
        begin_vars = dict(self.cur_fun.regs.vars)
        self.visit(tree.children[1])
        op = WhileOp(tree.children[1].op.out, mark)
        self._synth(op)
        self.visit(tree.children[3])
        self.visit(tree.children[2])  # 3rd statement
        for v, r in begin_vars.items():
            rvars = self.cur_fun.regs.vars
            if v not in rvars or rvars[v] != r:
                self._log(f'loading missing var {v}')
                self._synth(Load(self.cur_fun, [r, v]))
        self.cur_fun.ops.append(op.synth_endwhile)

    def _unary_op(op):
        def _f(self, tree):
            self.visit_children(tree)
            operand = tree.children[0].op.out
            reg = self.cur_fun.regs.take()
            tree.op = op(self.cur_fun, [reg, operand])
            self._synth(tree.op)
            self.cur_fun.regs.give(operand)
        return _f

    def dereference(self, tree):
        self.visit_children(tree)
        reg = tree.children[0].op.out
        var = Variable.from_dereference(reg)
        self._log(f'making var {var} from derefing reg {reg}')
        tree.var = var
        def delayed_load():
            self._log(f'delay-loading {tree.children[0]}')
            op = Load(self.cur_fun, [reg, var])
            self._synth(op)
            return op.out
        tree.op = Delayed(delayed_load)

    def post_increment(self, tree):
        self.visit_children(tree)
        tree.op = Reg(tree.children[0].op.out)
        var = tree.children[0].var
        reg = tree.op.out
        self.cur_fun.deferred_ops.append(Incr(self.cur_fun, [reg, reg]))
        self.cur_fun.deferred_ops.append(Store(self.cur_fun, [reg, var]))

    def post_decrement(self, tree):
        self.visit_children(tree)
        tree.op = Reg(tree.children[0].op.out)
        var = tree.children[0].var
        reg = tree.op.out
        self.cur_fun.deferred_ops.append(Decr(self.cur_fun, [reg, reg]))
        self.cur_fun.deferred_ops.append(Store(self.cur_fun, [reg, var]))

    pre_increment = _unary_op(Incr)
    bool_not = _unary_op(BoolNot)

    def _binary_op(op):
        def _f(self, tree):
            self.visit_children(tree)
            left, right = (x.op.out for x in tree.children)
            dest = self.cur_fun.regs.take()
            tree.op = op(self.cur_fun, [dest, left, right])
            self._synth(tree.op)
            self.cur_fun.regs.give(left)
            self.cur_fun.regs.give(right)
        return _f

    def _combo(uop, bop):
        def _f(self, tree):
            ftree = lark.Tree(bop, tree.children)
            tree.children = [ftree]
            uop.__get__(self)(tree)
        return _f

    shl = _binary_op(ShlOp)
    add = _binary_op(AddOp)
    sub = _binary_op(SubOp)
    mul = _binary_op(MulOp)
    _and = _binary_op(AndOp)
     # ...
    gt = _binary_op(GtOp)
    lt = _binary_op(LtOp)
    neq = _binary_op(NeqOp)
    eq = _combo(bool_not, 'neq')

    def _forward_op(self, tree):
        self.visit_children(tree)
        tree.op = tree.children[0].op

    def cast(self, tree):
        self.visit_children(tree)
        tree.op = tree.children[1].op

    def _log(self, line):
        self.cur_fun.log(line)

    def local_var(self, tree):
        self.visit_children(tree)
        assert self.cur_fun is not None
        assert self.cur_scope is not None
        var = Variable.from_def(tree)
        var.stackaddr = self.cur_fun.get_stack()  # will have to invert
        self.cur_scope.symbols[var.name] = var
        self.cur_fun.locals[var.name] = var
        if len(tree.children) > 2:
            initval = tree.children[2].children[0].op.out
            cleanup = lambda reg: self._synth(Store(self.cur_fun, [reg, var]))
            self.cur_fun.regs.assign(var, initval, cleanup)
            self._log(f'assigning {var} = {initval}')

    def fun_def(self, tree):
        prot, body = tree.children
        fun = Function(prot)
        assert self.cur_fun is None
        self.cur_fun = fun

        self.cur_scope.symbols[fun.spec.name] = fun.spec

        params = fun.param_dict()

        def getcleanup(var):
            return lambda reg: self._synth(Store(self.cur_fun, [reg, var]))

        for i, param in enumerate(fun.params):
            fun.locals[param.name] = param
            param.stackaddr = fun.get_stack()
            self._log(f'param [sp, {param.stackaddr}]: {param.name} in r{i}')
            cleanup = getcleanup(param)
            fun.regs.loaded(param, f'r{i}', cleanup)

        fun_scope = Scope()
        fun_scope.parent = self.cur_scope
        fun_scope.symbols.update(params)

        body.scope = fun_scope
        self.visit_children(tree)

        if fun.ret is None:
            if fun.spec.name == 'main':
                self._synth(Set16Imm(fun, ['r0', 0]))
                self._synth(ReturnReg(fun, ['r0']))
            elif fun.spec.return_type == 'void':
                self._synth(ReturnReg(fun, ['r0']))
            else:
                assert fun.ret is not None
        self.cur_fun = None
        self.funs.append(fun)

    def body(self, tree):
        bscope = getattr(tree, 'scope', Scope())
        bscope.parent = self.cur_scope
        self.cur_scope = bscope
        self.visit_children(tree)
        self.cur_scope = bscope.parent

    def return_stat(self, tree):
        assert self.cur_fun is not None
        self.cur_fun.ret = True
        self.visit_children(tree)
        expr_reg = tree.children[0].op.out
        tree.op = ReturnReg(self.cur_fun, [expr_reg])
        self._synth(tree.op)

preamble = [f'_start:',
        f'xor r0, r0, r0',
        f'xor r1, r1, r1',
        f'set sp, 0',
        f'seth sp, {0x11}',  # 256 bytes of stack ought to be enough
        f'set r2, main',
        f'set r3, 2',
        f'add lr, pc, r3',
        f'or pc, r2, r2',
        f'or pc, pc, pc  // loop forever',
        ]

def filter_dupes(ops):
    dupe_re = re.compile(r'or (r\d+), \1, \1')
    for op in ops:
        if dupe_re.search(op):
            continue
        yield op

def parse_tree(tree, debug=False):
    tr = CcTransform()
    tree = tr.transform(tree)

    if debug:
        print(tree.pretty())

    inte = CcInterp()
    inte.visit(tree)

    out = []

    for fun in inte.funs:
        out += fun.synth()
        out.append('')
    return '\n'.join(filter_dupes(out))


def larkparse(f, debug=False):
    with open(GRAMMAR_FILE) as g:
        asparser = lark.Lark(g.read())
    data = f.read()
    if isinstance(data, bytes):
        data = data.decode()
    tree = asparser.parse(data)
    return parse_tree(tree, debug=debug)


def parse_args():
    parser = argparse.ArgumentParser(description='Compile.')
    parser.add_argument('--debug', action='store_true',
                        help='print the AST')
    parser.add_argument('--assembly', '-S', action='store_true',
                        help='output assembly')
    parser.add_argument('--compile', '-c', action='store_true',
                        help='compile a single file')
    parser.add_argument('input', type=argparse.FileType('r'),
                        default=sys.stdin, help='input file (default: stdin)')
    parser.add_argument('--output', '-o', type=argparse.FileType('wb'),
                        default=sys.stdout.buffer, help='output file')
    return parser.parse_args()


def preprocess(fin):
    p = subprocess.Popen(CPP, stdin=fin, stdout=subprocess.PIPE)
    return p.stdout


def assemble(text, fout):
    fin = io.StringIO(text)
    asmod.write_obj(fout, *asmod.larkparse(fin))


def main():
    args = parse_args()

    assy = larkparse(preprocess(args.input), debug=args.debug)
    if args.assembly:
        args.output.write(assy.encode() + b'\n')
    else:
        assemble(assy, args.output)


if __name__ == "__main__":
    main()