wasmtime/lib/cretonne/meta/semantics/elaborate.py

"""
Tools to elaborate a given Rtl with concrete types into its semantically
equivalent primitive version. Its elaborated primitive version contains only
primitive cretonne instructions, which map well to SMTLIB functions.
"""
from .primitives import GROUP as PRIMITIVES, prim_to_bv, prim_from_bv
from cdsl.ti import ti_rtl, TypeEnv, get_type_env
from cdsl.typevar import TypeVar
from cdsl.xform import Rtl
from cdsl.ast import Var

try:
    from typing import TYPE_CHECKING, Dict, Union, List, Set, Tuple # noqa
    from cdsl.xform import XForm # noqa
    from cdsl.ast import Def, VarMap # noqa
    from cdsl.ti import VarTyping # noqa
except ImportError:
    TYPE_CHECKING = False


def is_rtl_concrete(r):
    # type: (Rtl) -> bool
    """Return True iff every Var in the Rtl r has a single type."""
    return all(v.get_typevar().singleton_type() is not None for v in r.vars())


def cleanup_concrete_rtl(r):
    # type: (Rtl) -> Rtl
    """
    Given an Rtl r
    1) assert that there is only 1 possible concrete typing T for r
    2) Assign a singleton TV with the single type t \in T for each Var v \in r
    """
    # 1) Infer the types of any of the remaining vars in res
    typenv = get_type_env(ti_rtl(r, TypeEnv()))
    typenv.normalize()
    typenv = typenv.extract()

    # 2) Make sure there is only one possible type assignment
    typings = list(typenv.concrete_typings())
    assert len(typings) == 1
    typing = typings[0]

    # 3) Assign the only possible type to each variable.
    for v in typenv.vars:
        if v.get_typevar().singleton_type() is not None:
            continue

        v.set_typevar(TypeVar.singleton(typing[v].singleton_type()))

    return r


def apply(r, x, suffix=None):
    # type: (Rtl, XForm, str) -> Rtl
    """
    Given a concrete Rtl r and XForm x, s.t. r matches x.src, return the
    corresponding concrete x.dst. If suffix is provided, any temporary defs are
    renamed with '.suffix' appended to their old name.
    """
    assert is_rtl_concrete(r)
    s = x.src.substitution(r, {})  # type: VarMap
    assert s is not None

    if (suffix is not None):
        for v in x.dst.vars():
            if v.is_temp():
                assert v not in s
                s[v] = Var(v.name + '.' + suffix)

    dst = x.dst.copy(s)
    return cleanup_concrete_rtl(dst)


def find_matching_xform(d):
    # type: (Def) -> XForm
    """
    Given a concrete Def d, find the unique semantic XForm x in
    d.expr.inst.semantics that applies to it.
    """
    res = []  # type: List[XForm]
    typing = {v:   v.get_typevar() for v in d.vars()}  # type: VarTyping

    for x in d.expr.inst.semantics:
        subst = d.substitution(x.src.rtl[0], {})

        # There may not be a substitution if there are concrete Enumerator
        # values in the src pattern. (e.g. specifying the semantics of icmp.eq,
        # icmp.ge... as separate transforms)
        if (subst is None):
            continue

        if x.ti.permits({subst[v]: tv for (v, tv) in typing.items()}):
            res.append(x)

    assert len(res) == 1
    return res[0]


def elaborate(r):
    # type: (Rtl) -> Rtl
    """
    Given an Rtl r, return a semantically equivalent Rtl r1 consisting only
    primitive instructions.
    """
    fp = False
    primitives = set(PRIMITIVES.instructions)
    idx = 0

    while not fp:
        assert is_rtl_concrete(r)
        new_defs = []  # type: List[Def]
        fp = True

        for d in r.rtl:
            inst = d.expr.inst

            if (inst not in primitives):
                transformed = apply(Rtl(d), find_matching_xform(d), str(idx))
                idx += 1
                new_defs.extend(transformed.rtl)
                fp = False
            else:
                new_defs.append(d)

        r.rtl = tuple(new_defs)

    return r


def cleanup_semantics(r, outputs):
    # type: (Rtl, Set[Var]) -> Rtl
    """
    The elaboration process creates a lot of redundant instruction pairs of the
    shape:

        a.0 << prim_from_bv(bva.0)
        ...
        bva.1 << prim_to_bv(a.0)
        ...

    Contract these to ease manual inspection.
    """
    new_defs = []  # type: List[Def]
    subst_m = {v: v for v in r.vars()}  # type: VarMap
    definition = {}  # type: Dict[Var, Def]

    # Pass 1: Remove redundant prim_to_bv
    for d in r.rtl:
        inst = d.expr.inst

        if (inst == prim_to_bv):
            if d.expr.args[0] in definition:
                assert isinstance(d.expr.args[0], Var)
                def_loc = definition[d.expr.args[0]]

                if def_loc.expr.inst == prim_from_bv:
                    assert isinstance(def_loc.expr.args[0], Var)
                    subst_m[d.defs[0]] = def_loc.expr.args[0]
                    continue

        new_def = d.copy(subst_m)

        for v in new_def.defs:
            assert v not in definition  # Guaranteed by SSA
            definition[v] = new_def

        new_defs.append(new_def)

    # Pass 2: Remove dead prim_from_bv
    live = set(outputs)  # type: Set[Var]
    for d in new_defs:
        live = live.union(d.uses())

    new_defs = [d for d in new_defs if not (d.expr.inst == prim_from_bv and
                                            d.defs[0] not in live)]

    return Rtl(*new_defs)