LlvmGenerator.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
    OpenGEODE - A tiny SDL Editor for TASTE

    This module generates LLVM IR code from SDL process models, allowing
    generation of a binary application without an intermediate language.
    LLVM also allows for various code verification, analysis, and optimization.

    The design is based on the Ada code generator. Check it for details.

    Copyright (c) 2012-2013 European Space Agency

    Designed and implemented by Maxime Perrotin

    Contact: maxime.perrotin@esa.int
"""

import logging
from singledispatch import singledispatch
from llvm import core, passes, ee

import ogAST
import Helper

LOG = logging.getLogger(__name__)

__all__ = ['generate']


# LLVM Global variable - Initialized when the generator is invoked
LLVM = {
    # The LLVM module, which holds all the IR code.
    'module': None,
    # Dictionary that keeps track of which values are defined in the current
    # scope and what their LLVM representation is.
    'named_values': {},
    # Dictionary that keeps track of the defined states and its integer
    # constant representation
    'states': {},
    # The builder used for the current function generation.
    'builder': None,
    # The function optimization passes manager.
    'pass_manager': None,
    # The LLVM execution engine.
    'executor': None,
    # ASN.1 data view
    'dataview': None,
    # Generated types
    'types': {},
    # Global strings
    'strings': {}
}


@singledispatch
def generate(ast):
    ''' Generate the code for an item of the AST '''
    raise TypeError('[Backend] Unsupported AST construct')


# Processing of the AST

@generate.register(ogAST.Process)
def _process(process):
    ''' Generate LLVM IR code '''

    process_name = str(process.processName)
    LOG.info('Generating LLVM IR code for process ' + str(process_name))

    # Initialize LLVM global structure
    LLVM['module'] = core.Module.new(process_name)
    LLVM['pass_manager'] = passes.FunctionPassManager.new(LLVM['module'])
    LLVM['executor'] = ee.ExecutionEngine.new(LLVM['module'])
    LLVM['dataview'] = process.dataview
    # Set up the optimizer pipeline.
    # Start with registering info about how the
    # target lays out data structures.
    #   LLVM['pass_manager'].add(LLVM['executor'].target_data)
    #   # Do simple "peephole" optimizations and bit-twiddling optzns.
    #   LLVM['pass_manager'].add(passes.PASS_INSTRUCTION_COMBINING)
    #   # Reassociate expressions.
    #   LLVM['pass_manager'].add(passes.PASS_REASSOCIATE)
    #   # Eliminate Common SubExpressions.
    #   LLVM['pass_manager'].add(passes.PASS_GVN)
    #   # Simplify the control flow graph (deleting unreachable blocks, etc).
    #   LLVM['pass_manager'].add(passes.PASS_CFG_SIMPLIFICATION)
    #   LLVM['pass_manager'].initialize()

    # Initialize built-in functions
    printf_type = core.Type.function(
        core.Type.void(),
        [core.Type.pointer(core.Type.int(8))], True
    )
    LLVM['module'].add_function(printf_type, 'printf')

    # In case model has nested states, flatten everything
    Helper.flatten(process)

    # Make an maping {input: {state: transition...}} in order to easily
    # generate the lookup tables for the state machine runtime
    mapping = Helper.map_input_state(process)

    # Initialize states enum
    for name in process.mapping.iterkeys():
        if not name.endswith('START'):
            cons = core.Constant.int(core.Type.int(), len(LLVM['states']))
            LLVM['states'][name] = cons

    # Generate state var
    LLVM['module'].add_global_variable(core.Type.int(), 'state')

    # Initialize output signals
    for signal in process.output_signals:
        param_tys = [core.Type.pointer(_generate_type(signal['type']))]
        func_ty = core.Type.function(core.Type.void(), param_tys)
        core.Function.new(LLVM['module'], func_ty, str(signal['name']))

    # Initialize external procedures
    for proc in [proc for proc in process.procedures if proc.external]:
        param_tys = [core.Type.pointer(_generate_type(p['type'])) for p in proc.fpar]
        func_ty = core.Type.function(core.Type.void(), param_tys)
        core.Function.new(LLVM['module'], func_ty, str(proc.inputString))

    # Generare process-level vars
    for var_name, (var_asn1_type, def_value) in process.variables.viewitems():
        var_type = _generate_type(var_asn1_type)
        LLVM['module'].add_global_variable(var_type, str(var_name).lower())
        if def_value:
            raise NotImplementedError

    # Generate process functions
    runtr_func = _generate_runtr_func(process)
    _generate_startup_func(process, process_name, runtr_func)

    # Generate input signals
    for signal in process.input_signals:
        _generate_input_signal(signal, mapping[signal['name']])

    print LLVM['module']


def _generate_runtr_func(process):
    ''' Generate code for the run_transition function '''
    func_name = 'run_transition'
    func_type = core.Type.function(core.Type.void(), [core.Type.int()])
    func = core.Function.new(LLVM['module'], func_type, func_name)

    entry_block = func.append_basic_block('entry')
    cond_block = func.append_basic_block('cond')
    body_block = func.append_basic_block('body')
    exit_block = func.append_basic_block('exit')

    builder = core.Builder.new(entry_block)
    LLVM['builder'] = builder

    # entry
    id_ptr = builder.alloca(core.Type.int(), None, 'id')
    LLVM['named_values']['id'] = id_ptr
    builder.store(func.args[0], id_ptr)
    builder.branch(cond_block)

    # cond
    builder.position_at_end(cond_block)
    id_ptr = func.args[0]
    no_tr_cons = core.Constant.int(core.Type.int(), -1)
    cond_val = builder.icmp(core.ICMP_NE, id_ptr, no_tr_cons, 'cond')
    builder.cbranch(cond_val, body_block, exit_block)

    # body
    builder.position_at_end(body_block)
    switch = builder.switch(func.args[0], exit_block)

    # transitions
    for idx, tr in enumerate(process.transitions):
        tr_block = func.append_basic_block('tr%d' % idx)
        const = core.Constant.int(core.Type.int(), idx)
        switch.add_case(const, tr_block)
        builder.position_at_end(tr_block)
        generate(tr)
        builder.branch(cond_block)

    # exit
    builder.position_at_end(exit_block)
    builder.ret_void()

    func.verify()
    LLVM['named_values'].clear()
    return func


def _generate_startup_func(process, process_name, runtr_func):
    ''' Generate code for the startup function '''
    func_name = process_name + '_startup'
    func_type = core.Type.function(core.Type.void(), [])
    func = core.Function.new(LLVM['module'], func_type, func_name)

    entry_block = func.append_basic_block('entry')
    builder = core.Builder.new(entry_block)
    LLVM['builder'] = builder

    # entry
    builder.call(runtr_func, [core.Constant.int(core.Type.int(), 0)])
    builder.ret_void()

    func.verify()
    return func


def _generate_input_signal(signal, inputs):
    ''' Generate code for an input signal '''
    func_name = str(signal['name'])
    param_tys = []
    if 'type' in signal:
        param_tys.append(core.Type.pointer(_generate_type(signal['type'])))
    func_type = core.Type.function(core.Type.void(), param_tys)
    func = core.Function.new(LLVM['module'], func_type, func_name)

    entry_block = func.append_basic_block('entry')
    exit_block = func.append_basic_block('exit')
    builder = core.Builder.new(entry_block)
    LLVM['builder'] = builder

    runtr_func = LLVM['module'].get_function_named('run_transition')

    g_state_val = builder.load(LLVM['module'].get_global_variable_named('state'))
    switch = builder.switch(g_state_val, exit_block)

    for state_name, state_id in LLVM['states'].iteritems():
        state_block = func.append_basic_block('state_%s' % str(state_name))
        switch.add_case(state_id, state_block)
        builder.position_at_end(state_block)

        # TODO: Nested states

        input = inputs.get(state_name)
        if input:
            for var_name in input.parameters:
                var_val = LLVM['module'].get_global_variable_named(str(var_name).lower())
                _generate_assign(var_val, func.args[0])
            if input.transition:
                id_val = core.Constant.int(core.Type.int(), input.transition_id)
                builder.call(runtr_func, [id_val])

        builder.ret_void()

    builder.position_at_end(exit_block)
    builder.ret_void()

    func.verify()


@generate.register(ogAST.Output)
@generate.register(ogAST.ProcedureCall)
def _call_external_function(output):
    ''' Generate the code of a set of output or procedure call statement '''

    for out in output.output:
        name = out['outputName'].lower()

        if name in ('write', 'writeln'):
            _generate_write(out['params'])
            continue
        elif name == 'reset_timer':
            _generate_reset_timer(out['params'])
            continue
        elif name == 'set_timer':
            _generate_set_timer(out['params'])
            continue

        func = LLVM['module'].get_function_named(str(name))
        LLVM['builder'].call(func, [expression(p) for p in out.get('params', [])])


def _generate_write(params):
    ''' Generate the code for the write operator '''
    zero = core.Constant.int(core.Type.int(), 0)
    for param in params:
        basic_ty = find_basic_type(param.exprType)
        expr_val = expression(param)
        printf_func = LLVM['module'].get_function_named('printf')
        if basic_ty.kind == 'IntegerType':
            fmt_val = _get_string_cons('%d')
            fmt_ptr = LLVM['builder'].gep(fmt_val, [zero, zero])
            LLVM['builder'].call(printf_func, [fmt_ptr, expr_val])
        elif basic_ty.kind == 'RealType':
            fmt_val = _get_string_cons('%.14E')
            fmt_ptr = LLVM['builder'].gep(fmt_val, [zero, zero])
            LLVM['builder'].call(printf_func, [fmt_ptr, expr_val])
        elif basic_ty.kind == 'BooleanType':
            true_str_val = _get_string_cons('true')
            true_str_ptr = LLVM['builder'].gep(true_str_val, [zero, zero])
            false_str_val = _get_string_cons('false')
            false_str_ptr = LLVM['builder'].gep(false_str_val, [zero, zero])
            str_ptr = LLVM['builder'].select(expr_val, true_str_ptr, false_str_ptr)
            LLVM['builder'].call(printf_func, [str_ptr])
        else:
            raise NotImplementedError


def _generate_writeln(params):
    ''' Generate the code for the writeln operator '''
    _generate_write(params)
    str_cons = _get_string_cons('\n')
    str_ptr = LLVM['builder'].gep(str_cons, [zero, zero])
    LLVM['builder'].call(printf_func, [str_ptr])


def _generate_reset_timer(params):
    ''' Generate the code for the reset timer operator '''
    raise NotImplementedError


def _generate_set_timer(params):
    ''' Generate the code for the set timer operator '''
    raise NotImplementedError


@generate.register(ogAST.TaskAssign)
def _task_assign(task):
    ''' Generate the code of a list of assignments '''
    for expr in task.elems:
        expression(expr)


@generate.register(ogAST.TaskInformalText)
def _task_informal_text(task):
    ''' Generate comments for informal text '''
    raise NotImplementedError


@generate.register(ogAST.TaskForLoop)
def _task_forloop(task):
    ''' Generate the code for a for loop '''
    raise NotImplementedError


# ------ expressions --------

@singledispatch
def expression(expr):
    ''' Generate the code for Expression-classes '''
    raise TypeError('Unsupported expression: ' + str(expr))


@expression.register(ogAST.PrimVariable)
def _primary_variable(prim):
    ''' Generate the code for a single variable reference '''
    return LLVM['module'].get_global_variable_named(str(prim.value[0]).lower())


@expression.register(ogAST.PrimPath)
def _prim_path(primary_id):
    ''' Generate the code for an of an element list (path) '''
    raise NotImplementedError


@expression.register(ogAST.ExprPlus)
@expression.register(ogAST.ExprMul)
@expression.register(ogAST.ExprMinus)
@expression.register(ogAST.ExprEq)
@expression.register(ogAST.ExprNeq)
@expression.register(ogAST.ExprGt)
@expression.register(ogAST.ExprGe)
@expression.register(ogAST.ExprLt)
@expression.register(ogAST.ExprLe)
@expression.register(ogAST.ExprDiv)
@expression.register(ogAST.ExprMod)
@expression.register(ogAST.ExprRem)
def _basic(expr):
    ''' Generate the code for an arithmetic of relational expression '''
    builder = LLVM['builder']
    lefttmp = expression(expr.left)
    righttmp = expression(expr.right)

    # load the value of the expression if it is a pointer
    if lefttmp.type.kind == core.TYPE_POINTER:
        lefttmp = builder.load(lefttmp, 'lefttmp')
    if righttmp.type.kind == core.TYPE_POINTER:
        righttmp = builder.load(righttmp, 'lefttmp')

    if lefttmp.type.kind != righttmp.type.kind:
        raise NotImplementedError

    if lefttmp.type.kind == core.TYPE_INTEGER:
        if expr.operand == '+':
            return builder.add(lefttmp, righttmp, 'addtmp')
        elif expr.operand == '-':
            return builder.sub(lefttmp, righttmp, 'subtmp')
        elif expr.operand == '*':
            return builder.mul(lefttmp, righttmp, 'multmp')
        elif expr.operand == '/':
            return builder.sdiv(lefttmp, righttmp, 'divtmp')
        elif expr.operand == 'mod':
            # l mod r == (((l rem r) + r) rem r)
            remtmp = builder.srem(lefttmp, righttmp)
            addtmp = builder.add(remtmp, righttmp)
            return builder.srem(addtmp, righttmp, 'modtmp')
        elif expr.operand == 'rem':
            return builder.srem(lefttmp, righttmp, 'remtmp')
        elif expr.operand == '<':
            return builder.icmp(core.ICMP_SLT, lefttmp, righttmp, 'lttmp')
        elif expr.operand == '<=':
            return builder.icmp(core.ICMP_SLE, lefttmp, righttmp, 'letmp')
        elif expr.operand == '=':
            return builder.icmp(core.ICMP_EQ, lefttmp, righttmp, 'eqtmp')
        elif expr.operand == '/=':
            return builder.icmp(core.ICMP_NE, lefttmp, righttmp, 'netmp')
        elif expr.operand == '>=':
            return builder.icmp(core.ICMP_SGE, lefttmp, righttmp, 'getmp')
        elif expr.operand == '>':
            return builder.icmp(core.ICMP_SGT, lefttmp, righttmp, 'gttmp')
        else:
            raise NotImplementedError
    elif lefttmp.type.kind == core.TYPE_DOUBLE:
        if expr.operand == '+':
            return builder.fadd(lefttmp, righttmp, 'addtmp')
        elif expr.operand == '-':
            return builder.fsub(lefttmp, righttmp, 'subtmp')
        elif expr.operand == '*':
            return builder.fmul(lefttmp, righttmp, 'multmp')
        elif expr.operand == '/':
            return builder.fdiv(lefttmp, righttmp, 'divtmp')
        elif expr.operand == 'mod':
            # l mod r == (((l rem r) + r) rem r)
            remtmp = builder.frem(lefttmp, righttmp)
            addtmp = builder.fadd(remtmp, righttmp)
            return builder.frem(addtmp, righttmp, 'modtmp')
        elif expr.operand == 'rem':
            return builder.frem(lefttmp, righttmp, 'remtmp')
        elif expr.operand == '<':
            return builder.icmp(core.FCMP_OLT, lefttmp, righttmp, 'lttmp')
        elif expr.operand == '<=':
            return builder.icmp(core.FCMP_OLE, lefttmp, righttmp, 'letmp')
        elif expr.operand == '=':
            return builder.icmp(core.FCMP_OEQ, lefttmp, righttmp, 'eqtmp')
        elif expr.operand == '/=':
            return builder.icmp(core.FCMP_ONE, lefttmp, righttmp, 'netmp')
        elif expr.operand == '>=':
            return builder.icmp(core.FCMP_OGE, lefttmp, righttmp, 'getmp')
        elif expr.operand == '>':
            return builder.icmp(core.FCMP_OGT, lefttmp, righttmp, 'gttmp')
        else:
            raise NotImplementedError
    else:
        raise NotImplementedError


@expression.register(ogAST.ExprAssign)
def _assign(expr):
    ''' Generate the code for an assign expression '''
    left = expression(expr.left)
    right = expression(expr.right)
    _generate_assign(left, right)
    return left


def _generate_assign(left, right):
    ''' Generate code for an assign from two LLVM values'''
    # This is extracted as an standalone function because is used by
    # multiple generation rules
    builder = LLVM['builder']
    if left.type.kind == core.TYPE_POINTER and left.type.pointee.kind == core.TYPE_STRUCT:
        memcpy = _get_memcpy_intrinsic()

        size = core.Constant.int(core.Type.int(64), 2)
        align = core.Constant.int(core.Type.int(32), 1)
        volatile = core.Constant.int(core.Type.int(1), 0)

        right_ptr = builder.bitcast(right, core.Type.pointer(core.Type.int(8)))
        left_ptr = builder.bitcast(left, core.Type.pointer(core.Type.int(8)))

        builder.call(memcpy, [left_ptr, right_ptr, size, align, volatile])
    else:
        builder.store(right, left)


@expression.register(ogAST.ExprOr)
@expression.register(ogAST.ExprAnd)
@expression.register(ogAST.ExprXor)
def _logical(expr):
    ''' Generate the code for a logical expression '''
    builder = LLVM['builder']

    lefttmp = expression(expr.left)
    righttmp = expression(expr.right)

    ty = find_basic_type(expr.exprType)
    if ty.kind != 'BooleanType':
        raise NotImplementedError

    # load the value of the expression if it is a pointer
    if lefttmp.type.kind == core.TYPE_POINTER:
        lefttmp = builder.load(lefttmp, 'lefttmp')
    if righttmp.type.kind == core.TYPE_POINTER:
        righttmp = builder.load(righttmp, 'lefttmp')

    if expr.operand == '&&':
        return builder.and_(lefttmp, righttmp, 'ortmp')
    elif expr.operand == '||':
        return builder.or_(lefttmp, righttmp, 'ortmp')
    else:
        return builder.xor(lefttmp, righttmp, 'xortmp')


@expression.register(ogAST.ExprAppend)
def _append(expr):
    ''' Generate code for the APPEND construct: a // b '''
    raise NotImplementedError


@expression.register(ogAST.ExprIn)
def _expr_in(expr):
    ''' Generate the code for an in expression '''
    raise NotImplementedError


@expression.register(ogAST.PrimEnumeratedValue)
def _enumerated_value(primary):
    ''' Generate code for an enumerated value '''
    raise NotImplementedError


@expression.register(ogAST.PrimChoiceDeterminant)
def _choice_determinant(primary):
    ''' Generate code for a choice determinant (enumerated) '''
    raise NotImplementedError


@expression.register(ogAST.PrimInteger)
def _integer(primary):
    ''' Generate code for a raw integer value  '''
    return core.Constant.int(core.Type.int(), primary.value[0])


@expression.register(ogAST.PrimReal)
def _real(primary):
    ''' Generate code for a raw real value  '''
    return core.Constant.real(core.Type.double(), primary.value[0])


@expression.register(ogAST.PrimBoolean)
def _boolean(primary):
    ''' Generate code for a raw boolean value  '''
    if primary.value[0].lower() == 'true':
        return core.Constant.int(core.Type.int(1), 1)
    else:
        return core.Constant.int(core.Type.int(1), 0)


@expression.register(ogAST.PrimEmptyString)
def _empty_string(primary):
    ''' Generate code for an empty SEQUENCE OF: {} '''
    raise NotImplementedError


@expression.register(ogAST.PrimStringLiteral)
def _string_literal(primary):
    ''' Generate code for a string (Octet String) '''
    raise NotImplementedError


@expression.register(ogAST.PrimConstant)
def _constant(primary):
    ''' Generate code for a reference to an ASN.1 constant '''
    raise NotImplementedError


@expression.register(ogAST.PrimMantissaBaseExp)
def _mantissa_base_exp(primary):
    ''' Generate code for a Real with Mantissa-base-Exponent representation '''
    raise NotImplementedError


@expression.register(ogAST.PrimIfThenElse)
def _if_then_else(ifthen):
    ''' Generate the code for ternary operator '''
    raise NotImplementedError


@expression.register(ogAST.PrimSequence)
def _sequence(seq):
    ''' Generate the code for an ASN.1 SEQUENCE '''
    raise NotImplementedError


@expression.register(ogAST.PrimSequenceOf)
def _sequence_of(seqof):
    ''' Generate the code for an ASN.1 SEQUENCE OF '''
    builder = LLVM['builder']

    ty = _generate_type(seqof.exprType)
    struct_ptr = builder.alloca(ty)
    zero_cons = core.Constant.int(core.Type.int(), 0)
    array_ptr = builder.gep(struct_ptr, [zero_cons, zero_cons])

    for idx, expr in enumerate(seqof.value):
        idx_cons = core.Constant.int(core.Type.int(), idx)
        expr_val = expression(expr)
        pos_ptr = builder.gep(array_ptr, [zero_cons, idx_cons])
        builder.store(expr_val, pos_ptr)

    return struct_ptr


@expression.register(ogAST.PrimChoiceItem)
def _choiceitem(choice):
    ''' Generate the code for a CHOICE expression '''
    raise NotImplementedError


@generate.register(ogAST.Decision)
def _decision(dec):
    ''' Generate the code for a decision '''
    builder = LLVM['builder']
    func = builder.basic_block.function

    ans_cond_blocks = [func.append_basic_block('ans_cond') for ans in dec.answers]
    end_block = func.append_basic_block('end')

    builder.branch(ans_cond_blocks[0])

    for idx, ans in enumerate(dec.answers):
        ans_cond_block = ans_cond_blocks[idx]
        if ans.transition:
            ans_tr_block = func.append_basic_block('ans_tr')
        builder.position_at_end(ans_cond_block)

        if ans.kind == 'constant':
            next_block = ans_cond_blocks[idx+1] if idx < len(ans_cond_blocks) else end_block

            expr = ans.openRangeOp()
            expr.left = dec.question
            expr.right = ans.constant
            expr_val = expression(expr)

            true_cons = core.Constant.int(core.Type.int(1), 1)
            cond_val = builder.icmp(core.ICMP_EQ, expr_val, true_cons)
            builder.cbranch(cond_val, ans_tr_block if ans.transition else end_block, next_block)
        elif ans.kind == 'else':
            if ans.transition:
                builder.branch(ans_tr_block)
            else:
                builder.branch(end_block)
        else:
            raise NotImplementedError

        if ans.transition:
            builder.position_at_end(ans_tr_block)
            generate(ans.transition)
            builder.branch(end_block)

    builder.position_at_end(end_block)


@generate.register(ogAST.Label)
def _label(tr):
    ''' TGenerate the code for a Label '''
    raise NotImplementedError


@generate.register(ogAST.Transition)
def _transition(tr):
    ''' Generate the code for a transition '''
    for action in tr.actions:
        generate(action)
        if isinstance(action, ogAST.Label):
            return
    if tr.terminator:
        _generate_terminator(tr.terminator)


def _generate_terminator(term):
    ''' Generate the code for a transition termiantor '''
    builder = LLVM['builder']
    id_ptr = LLVM['named_values']['id']
    if term.label:
        raise NotImplementedError
    if term.kind == 'next_state':
        state = term.inputString.lower()
        if state.strip() != '-':
            next_id_cons = core.Constant.int(core.Type.int(), term.next_id)
            builder.store(next_id_cons, id_ptr)
            if term.next_id == -1:
                state_ptr = LLVM['module'].get_global_variable_named('state')
                state_id_cons = LLVM['states'][state]
                builder.store(state_id_cons, state_ptr)
        else:
            raise NotImplementedError
    elif term.kind == 'join':
        raise NotImplementedError
    elif term.kind == 'stop':
        raise NotImplementedError
    elif term.kind == 'return':
        raise NotImplementedError


@generate.register(ogAST.Floating_label)
def _floating_label(label):
    ''' Generate the code for a floating label '''
    raise NotImplementedError


@generate.register(ogAST.Procedure)
def _inner_procedure(proc):
    ''' Generate the code for a procedure '''
    raise NotImplementedError


def _generate_type(ty):
    ''' Generate the equivalent LLVM type of a ASN.1 type '''
    basic_ty = find_basic_type(ty)
    if basic_ty.kind == 'IntegerType':
        return core.Type.int()
    elif basic_ty.kind == 'BooleanType':
        return core.Type.int(1)
    elif basic_ty.kind == 'RealType':
        return core.Type.double()
    elif basic_ty.kind == 'SequenceOfType':
        if ty.ReferencedTypeName in LLVM['types']:
            return LLVM['types'][ty.ReferencedTypeName]

        min_size = int(basic_ty.Max)
        max_size = int(basic_ty.Min)
        if min_size != max_size:
            raise NotImplementedError

        elem_ty = _generate_type(basic_ty.type)
        array_ty = core.Type.array(elem_ty, max_size)
        struct_ty = core.Type.struct([array_ty], ty.ReferencedTypeName)
        LLVM['types'][ty.ReferencedTypeName] = struct_ty
        return struct_ty
    else:
        raise NotImplementedError


def _get_string_cons(str):
    ''' Returns a reference to a global string constant with the given value '''
    if str in LLVM['strings']:
        return LLVM['strings'][str]

    str_val = core.Constant.stringz(str)
    # TODO: This names can cause conflicts with user defined variables
    gvar_name = 'str_%s' % len(LLVM['strings'])
    gvar_val = LLVM['module'].add_global_variable(str_val.type, gvar_name)
    gvar_val.initializer = str_val
    LLVM['strings'][str] = gvar_val
    return gvar_val


def _get_memcpy_intrinsic():
    ''' Return the LLVM Memcpy Intrinsic '''
    arg_tys = [
        core.Type.pointer(core.Type.int(8)),
        core.Type.pointer(core.Type.int(8)),
        core.Type.int(64)
    ]
    return core.Function.intrinsic(LLVM['module'], core.INTR_MEMCPY, arg_tys)


# TODO: Refactor this into the helper module
def find_basic_type(a_type):
    ''' Return the ASN.1 basic type of a_type '''
    basic_type = a_type
    while basic_type.kind == 'ReferenceType':
        # Find type with proper case in the data view
        for typename in LLVM['dataview'].viewkeys():
            if typename.lower() == basic_type.ReferencedTypeName.lower():
                basic_type = LLVM['dataview'][typename].type
                break
    return basic_type