"""
Generate sources for instruction encoding.

The tables and functions generated here support the `TargetISA::encode()`
function which determines if a given instruction is legal, and if so, it's
`Encoding` data which consists of a *recipe* and some *encoding* bits.

The `encode` function doesn't actually generate the binary machine bits. Each
recipe has a corresponding hand-written function to do that after registers
are allocated.

This is the information available to us:

- The instruction to be encoded as an `Inst` reference.
- The data-flow graph containing the instruction, giving us access to the
  `InstructionData` representation and the types of all values involved.
- A target ISA instance with shared and ISA-specific settings for evaluating
  ISA predicates.
- The currently active CPU mode is determined by the ISA.

## Level 1 table lookup

The CPU mode provides the first table. The key is the instruction's controlling
type variable. If the instruction is not polymorphic, use `VOID` for the type
variable. The table values are level 2 tables.

## Level 2 table lookup

The level 2 table is keyed by the instruction's opcode. The table values are
*encoding lists*.

The two-level table lookup allows the level 2 tables to be much smaller with
good locality. Code in any given function usually only uses a few different
types, so many of the level 2 tables will be cold.

## Encoding lists

An encoding list is a non-empty sequence of list entries. Each entry has
one of these forms:

1. Instruction predicate, encoding recipe, and encoding bits. If the
   instruction predicate is true, use this recipe and bits.
2. ISA predicate and skip-count. If the ISA predicate is false, skip the next
   *skip-count* entries in the list. If the skip count is zero, stop
   completely.
3. Stop. End of list marker. If this is reached, the instruction does not have
   a legal encoding.

The instruction predicate is also used to distinguish between polymorphic
instructions with different types for secondary type variables.
"""
from __future__ import absolute_import
import srcgen
from constant_hash import compute_quadratic
from unique_table import UniqueSeqTable
from collections import OrderedDict, defaultdict
import math
import itertools
from cdsl.registers import RegClass, Register
from cdsl.predicates import FieldPredicate

try:
    from typing import Sequence, Set, Tuple, List, Iterable, DefaultDict, TYPE_CHECKING  # noqa
    if TYPE_CHECKING:
        from cdsl.isa import TargetISA, OperandConstraint, Encoding, CPUMode  # noqa
        from cdsl.predicates import PredNode, PredLeaf  # noqa
        from cdsl.types import ValueType  # noqa
        from cdsl.instructions import Instruction  # noqa
except ImportError:
    pass


def emit_instp(instp, fmt):
    # type: (PredNode, srcgen.Formatter) -> None
    """
    Emit code for matching an instruction predicate against an
    `InstructionData` reference called `inst`.

    The generated code is a pattern match that falls through if the instruction
    has an unexpected format. This should lead to a panic.
    """
    iform = instp.predicate_context()

    # Which fields do we need in the InstructionData pattern match?
    # Collect the leaf predicates.
    leafs = set()  # type: Set[PredLeaf]
    instp.predicate_leafs(leafs)
    # All the leafs are FieldPredicate instances. Here we just care about
    # the field names.
    fnames = set()  # type: Set[str]
    for p in leafs:
        assert isinstance(p, FieldPredicate)
        fnames.add(p.field.rust_name())
    fields = ', '.join(sorted(fnames))

    with fmt.indented('{} => {{'.format(instp.number), '}'):
        with fmt.indented(
                'if let InstructionData::{} {{ {}, .. }} = *inst {{'
                .format(iform.name, fields), '}'):
            fmt.line('return {};'.format(instp.rust_predicate(0)))


def emit_instps(instps, fmt):
    # type: (Sequence[PredNode], srcgen.Formatter) -> None
    """
    Emit a function for matching instruction predicates.
    """

    if not instps:
        # If the ISA has no predicates, just emit a stub.
        with fmt.indented(
                'pub fn check_instp(_: &InstructionData, _: u16) ' +
                '-> bool {', '}'):
            fmt.line('unimplemented!()')
        return

    with fmt.indented(
            'pub fn check_instp(inst: &InstructionData, instp_idx: u16) ' +
            '-> bool {', '}'):
        # The matches emitted by `emit_instp` need this.
        fmt.line('use ir::instructions::InstructionFormat;')
        with fmt.indented('match instp_idx {', '}'):
            for instp in instps:
                emit_instp(instp, fmt)
            fmt.line('_ => panic!("Invalid instruction predicate")')

        # The match cases will fall through if the instruction format is wrong.
        fmt.line('panic!("Bad format {:?}/{} for instp {}",')
        fmt.line('       InstructionFormat::from(inst),')
        fmt.line('       inst.opcode(),')
        fmt.line('       instp_idx);')


# Encoding lists are represented as u16 arrays.
CODE_BITS = 16
PRED_BITS = 12
PRED_MASK = (1 << PRED_BITS) - 1

# 0..CODE_ALWAYS means: Check instruction predicate and use the next two
# entries as a (recipe, encbits) pair if true. CODE_ALWAYS is the always-true
# predicate, smaller numbers refer to instruction predicates.
CODE_ALWAYS = PRED_MASK

# Codes above CODE_ALWAYS indicate an ISA predicate to be tested.
# `x & PRED_MASK` is the ISA predicate number to test.
# `(x >> PRED_BITS)*3` is the number of u16 table entries to skip if the ISA
# predicate is false. (The factor of three corresponds to the (inst-pred,
# recipe, encbits) triples.
#
# Finally, CODE_FAIL indicates the end of the list.
CODE_FAIL = (1 << CODE_BITS) - 1


def seq_doc(enc):
    # type: (Encoding) -> Tuple[Tuple[int, int, int], str]
    """
    Return a tuple containing u16 representations of the instruction predicate
    an recipe / encbits.

    Also return a doc string.
    """
    if enc.instp:
        p = enc.instp.number
        doc = '--> {} when {}'.format(enc, enc.instp)
    else:
        p = CODE_ALWAYS
        doc = '--> {}'.format(enc)
    assert p <= CODE_ALWAYS
    return ((p, enc.recipe.number, enc.encbits), doc)


class EncList(object):
    """
    List of instructions for encoding a given type + opcode pair.

    An encoding list contains a sequence of predicates and encoding recipes,
    all encoded as u16 values.

    :param inst: The instruction opcode being encoded.
    :param ty: Value of the controlling type variable, or `None`.
    """

    def __init__(self, inst, ty):
        # type: (Instruction, ValueType) -> None
        self.inst = inst
        self.ty = ty
        # List of applicable Encoding instances.
        # These will have different predicates.
        self.encodings = []  # type: List[Encoding]

    def name(self):
        # type: () -> str
        name = self.inst.name
        if self.ty:
            name = '{}.{}'.format(name, self.ty.name)
        if self.encodings:
            name += ' ({})'.format(self.encodings[0].cpumode)
        return name

    def by_isap(self):
        # type: () -> Iterable[Tuple[PredNode, Tuple[Encoding, ...]]]
        """
        Group the encodings by ISA predicate without reordering them.

        Yield a sequence of `(isap, (encs...))` tuples where `isap` is the ISA
        predicate or `None`, and `(encs...)` is a tuple of encodings that all
        have the same ISA predicate.
        """
        maxlen = CODE_FAIL >> PRED_BITS
        for isap, groupi in itertools.groupby(
                self.encodings, lambda enc: enc.isap):
            group = tuple(groupi)
            # This probably never happens, but we can't express more than
            # maxlen encodings per isap.
            while len(group) > maxlen:
                yield (isap, group[0:maxlen])
                group = group[maxlen:]
            yield (isap, group)

    def encode(self, seq_table, doc_table, isa):
        # type: (UniqueSeqTable, DefaultDict[int, List[str]], TargetISA) -> None  # noqa
        """
        Encode this list as a sequence of u16 numbers.

        Adds the sequence to `seq_table` and records the returned offset as
        `self.offset`.

        Adds comment lines to `doc_table` keyed by seq_table offsets.
        """
        words = list()  # type: List[int]
        docs = list()  # type: List[Tuple[int, str]]

        # Group our encodings by isap.
        for isap, group in self.by_isap():
            if isap:
                # We have an ISA predicate covering `glen` encodings.
                pnum = isa.settings.predicate_number[isap]
                glen = len(group)
                doc = 'skip {}x3 unless {}'.format(glen, isap)
                docs.append((len(words), doc))
                words.append((glen << PRED_BITS) | pnum)

            for enc in group:
                seq, doc = seq_doc(enc)
                docs.append((len(words), doc))
                words.extend(seq)

        # Terminate the list.
        words.append(CODE_FAIL)

        self.offset = seq_table.add(words)

        # Add doc comments.
        doc_table[self.offset].append(
                '{:06x}: {}'.format(self.offset, self.name()))
        for pos, doc in docs:
            doc_table[self.offset + pos].append(doc)


class Level2Table(object):
    """
    Level 2 table mapping instruction opcodes to `EncList` objects.

    :param ty: Controlling type variable of all entries, or `None`.
    """

    def __init__(self, ty):
        # type: (ValueType) -> None
        self.ty = ty
        # Maps inst -> EncList
        self.lists = OrderedDict()  # type: OrderedDict[Instruction, EncList]

    def __getitem__(self, inst):
        # type: (Instruction) -> EncList
        ls = self.lists.get(inst)
        if not ls:
            ls = EncList(inst, self.ty)
            self.lists[inst] = ls
        return ls

    def enclists(self):
        # type: () -> Iterable[EncList]
        return iter(self.lists.values())

    def layout_hashtable(self, level2_hashtables, level2_doc):
        # type: (List[EncList], DefaultDict[int, List[str]]) -> None
        """
        Compute the hash table mapping opcode -> enclist.

        Append the hash table to `level2_hashtables` and record the offset.
        """
        def hash_func(enclist):
            # type: (EncList) -> int
            return enclist.inst.number
        hash_table = compute_quadratic(self.lists.values(), hash_func)

        self.hash_table_offset = len(level2_hashtables)
        self.hash_table_len = len(hash_table)

        level2_doc[self.hash_table_offset].append(
                '{:06x}: {}, {} entries'.format(
                    self.hash_table_offset,
                    self.ty,
                    self.hash_table_len))
        level2_hashtables.extend(hash_table)


class Level1Table(object):
    """
    Level 1 table mapping types to `Level2` objects.
    """

    def __init__(self):
        # type: () -> None
        self.tables = OrderedDict()  # type: OrderedDict[ValueType, Level2Table]  # noqa

    def __getitem__(self, ty):
        # type: (ValueType) -> Level2Table
        tbl = self.tables.get(ty)
        if not tbl:
            tbl = Level2Table(ty)
            self.tables[ty] = tbl
        return tbl

    def l2tables(self):
        # type: () -> Iterable[Level2Table]
        return iter(self.tables.values())


def make_tables(cpumode):
    # type: (CPUMode) -> Level1Table
    """
    Generate tables for `cpumode` as described above.
    """
    table = Level1Table()
    for enc in cpumode.encodings:
        ty = enc.ctrl_typevar()
        inst = enc.inst
        table[ty][inst].encodings.append(enc)
    return table


def encode_enclists(level1, seq_table, doc_table, isa):
    # type: (Level1Table, UniqueSeqTable, DefaultDict[int, List[str]], TargetISA) -> None  # noqa
    """
    Compute encodings and doc comments for encoding lists in `level1`.
    """
    for level2 in level1.l2tables():
        for enclist in level2.enclists():
            enclist.encode(seq_table, doc_table, isa)


def emit_enclists(seq_table, doc_table, fmt):
    # type: (UniqueSeqTable, DefaultDict[int, List[str]], srcgen.Formatter) -> None  # noqa
    with fmt.indented(
            'pub static ENCLISTS: [u16; {}] = ['.format(len(seq_table.table)),
            '];'):
        line = ''
        for idx, entry in enumerate(seq_table.table):
            if idx in doc_table:
                if line:
                    fmt.line(line)
                    line = ''
                for doc in doc_table[idx]:
                    fmt.comment(doc)
            line += '{:#06x}, '.format(entry)
        if line:
            fmt.line(line)


def encode_level2_hashtables(level1, level2_hashtables, level2_doc):
    # type: (Level1Table, List[EncList], DefaultDict[int, List[str]]) -> None
    for level2 in level1.l2tables():
        level2.layout_hashtable(level2_hashtables, level2_doc)


def emit_level2_hashtables(level2_hashtables, offt, level2_doc, fmt):
    # type: (List[EncList], str, DefaultDict[int, List[str]], srcgen.Formatter) -> None  # noqa
    """
    Emit the big concatenation of level 2 hash tables.
    """
    with fmt.indented(
            'pub static LEVEL2: [Level2Entry<{}>; {}] = ['
            .format(offt, len(level2_hashtables)),
            '];'):
        for offset, entry in enumerate(level2_hashtables):
            if offset in level2_doc:
                for doc in level2_doc[offset]:
                    fmt.comment(doc)
            if entry:
                fmt.line(
                        'Level2Entry ' +
                        '{{ opcode: Some(Opcode::{}), offset: {:#08x} }},'
                        .format(entry.inst.camel_name, entry.offset))
            else:
                fmt.line(
                        'Level2Entry ' +
                        '{ opcode: None, offset: 0 },')


def emit_level1_hashtable(cpumode, level1, offt, fmt):
    # type: (CPUMode, Level1Table, str, srcgen.Formatter) -> None  # noqa
    """
    Emit a level 1 hash table for `cpumode`.
    """
    def hash_func(level2):
        # type: (Level2Table) -> int
        return level2.ty.number if level2.ty is not None else 0
    hash_table = compute_quadratic(level1.tables.values(), hash_func)

    with fmt.indented(
            'pub static LEVEL1_{}: [Level1Entry<{}>; {}] = ['
            .format(cpumode.name.upper(), offt, len(hash_table)), '];'):
        for level2 in hash_table:
            if level2:
                l2l = int(math.log(level2.hash_table_len, 2))
                assert l2l > 0, "Hash table too small"
                tyname = level2.ty.name if level2.ty is not None else 'void'
                fmt.line(
                        'Level1Entry ' +
                        '{{ ty: types::{}, log2len: {}, offset: {:#08x} }},'
                        .format(
                            tyname.upper(),
                            l2l,
                            level2.hash_table_offset))
            else:
                # Empty entry.
                fmt.line(
                        'Level1Entry ' +
                        '{ ty: types::VOID, log2len: 0, offset: 0 },')


def offset_type(length):
    # type: (int) -> str
    """
    Compute an appropriate Rust integer type to use for offsets into a table of
    the given length.
    """
    if length <= 0x10000:
        return 'u16'
    else:
        assert length <= 0x100000000, "Table too big"
        return 'u32'


def emit_recipe_names(isa, fmt):
    # type: (TargetISA, srcgen.Formatter) -> None
    """
    Emit a table of encoding recipe names keyed by recipe number.

    This is used for pretty-printing encodings.
    """
    with fmt.indented(
            'static RECIPE_NAMES: [&\'static str; {}] = ['
            .format(len(isa.all_recipes)), '];'):
        for r in isa.all_recipes:
            fmt.line('"{}",'.format(r.name))


def emit_recipe_constraints(isa, fmt):
    # type: (TargetISA, srcgen.Formatter) -> None
    """
    Emit a table of encoding recipe operand constraints keyed by recipe number.

    These are used by the register allocator to pick registers that can be
    properly encoded.
    """
    with fmt.indented(
            'static RECIPE_CONSTRAINTS: [RecipeConstraints; {}] = ['
            .format(len(isa.all_recipes)), '];'):
        for r in isa.all_recipes:
            fmt.comment(r.name)
            with fmt.indented('RecipeConstraints {', '},'):
                emit_operand_constraints(r.ins, 'ins', fmt)
                emit_operand_constraints(r.outs, 'outs', fmt)


def emit_operand_constraints(seq, field, fmt):
    # type: (Sequence[OperandConstraint], str, srcgen.Formatter) -> None
    """
    Emit a struct field initializer for an array of operand constraints.
    """
    if len(seq) == 0:
        fmt.line('{}: &[],'.format(field))
        return
    with fmt.indented('{}: &['.format(field), '],'):
        for cons in seq:
            with fmt.indented('OperandConstraint {', '},'):
                if isinstance(cons, RegClass):
                    fmt.line('kind: ConstraintKind::Reg,')
                    fmt.line('regclass: {},'.format(cons))
                elif isinstance(cons, Register):
                    fmt.line(
                            'kind: ConstraintKind::FixedReg({}),'
                            .format(cons.unit))
                    fmt.line('regclass: {},'.format(cons.regclass))
                else:
                    raise AssertionError(
                            'Unsupported constraint {}'.format(cons))


def emit_recipe_sizing(isa, fmt):
    # type: (TargetISA, srcgen.Formatter) -> None
    """
    Emit a table of encoding recipe code size information.
    """
    with fmt.indented(
            'static RECIPE_SIZING: [RecipeSizing; {}] = ['
            .format(len(isa.all_recipes)), '];'):
        for r in isa.all_recipes:
            fmt.comment(r.name)
            with fmt.indented('RecipeSizing {', '},'):
                fmt.format('bytes: {},', r.size)
                if r.branch_range:
                    fmt.format(
                        'branch_range: '
                        'Some(BranchRange {{ origin: {}, bits: {} }}),',
                        *r.branch_range)
                else:
                    fmt.line('branch_range: None,')


def gen_isa(isa, fmt):
    # type: (TargetISA, srcgen.Formatter) -> None
    # First assign numbers to relevant instruction predicates and generate the
    # check_instp() function..
    emit_instps(isa.all_instps, fmt)

    # Level1 tables, one per CPU mode
    level1_tables = dict()

    # Tables for enclists with comments.
    seq_table = UniqueSeqTable()
    doc_table = defaultdict(list)  # type: DefaultDict[int, List[str]]

    # Single table containing all the level2 hash tables.
    level2_hashtables = list()  # type: List[EncList]
    level2_doc = defaultdict(list)  # type: DefaultDict[int, List[str]]

    for cpumode in isa.cpumodes:
        level2_doc[len(level2_hashtables)].append(cpumode.name)
        level1 = make_tables(cpumode)
        level1_tables[cpumode] = level1
        encode_enclists(level1, seq_table, doc_table, isa)
        encode_level2_hashtables(level1, level2_hashtables, level2_doc)

    # Level 1 table encodes offsets into the level 2 table.
    level1_offt = offset_type(len(level2_hashtables))
    # Level 2 tables encodes offsets into seq_table.
    level2_offt = offset_type(len(seq_table.table))

    emit_enclists(seq_table, doc_table, fmt)
    emit_level2_hashtables(level2_hashtables, level2_offt, level2_doc, fmt)
    for cpumode in isa.cpumodes:
        emit_level1_hashtable(
                cpumode, level1_tables[cpumode], level1_offt, fmt)

    emit_recipe_names(isa, fmt)
    emit_recipe_constraints(isa, fmt)
    emit_recipe_sizing(isa, fmt)

    # Finally, tie it all together in an `EncInfo`.
    with fmt.indented('pub static INFO: EncInfo = EncInfo {', '};'):
        fmt.line('constraints: &RECIPE_CONSTRAINTS,')
        fmt.line('sizing: &RECIPE_SIZING,')
        fmt.line('names: &RECIPE_NAMES,')


def generate(isas, out_dir):
    # type: (Sequence[TargetISA], str) -> None
    for isa in isas:
        fmt = srcgen.Formatter()
        gen_isa(isa, fmt)
        fmt.update_file('encoding-{}.rs'.format(isa.name), out_dir)