89ff979d75
Consolidate the imm_members and imm_kinds into this list so the FormatField is the single definition of these properties. This makes it easier to access the precomputed FormatFields parametrically, avoiding going through getattr(). This is better for type checking too.
295 lines
8.9 KiB
Python
295 lines
8.9 KiB
Python
"""
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Cretonne predicates.
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A *predicate* is a function that computes a boolean result. The inputs to the
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function determine the kind of predicate:
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- An *ISA predicate* is evaluated on the current ISA settings together with the
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shared settings defined in the :py:mod:`settings` module. Once a target ISA
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has been configured, the value of all ISA predicates is known.
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- An *Instruction predicate* is evaluated on an instruction instance, so it can
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inspect all the immediate fields and type variables of the instruction.
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Instruction predicates can be evaluated before register allocation, so they
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can not depend on specific register assignments to the value operands or
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outputs.
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Predicates can also be computed from other predicates using the `And`, `Or`,
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and `Not` combinators defined in this module.
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All predicates have a *context* which determines where they can be evaluated.
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For an ISA predicate, the context is the ISA settings group. For an instruction
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predicate, the context is the instruction format.
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"""
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from __future__ import absolute_import
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from functools import reduce
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try:
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from typing import Sequence, Tuple, Set, Any, Union, TYPE_CHECKING # noqa
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if TYPE_CHECKING:
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from .formats import InstructionFormat, FormatField # noqa
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from .settings import BoolSetting, SettingGroup # noqa
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PredContext = Union[SettingGroup, InstructionFormat]
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PredLeaf = Union[BoolSetting, 'FieldPredicate']
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PredNode = Union[PredLeaf, 'Predicate']
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except ImportError:
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pass
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def _is_parent(a, b):
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# type: (PredContext, PredContext) -> bool
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"""
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Return true if a is a parent of b, or equal to it.
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"""
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while b and a is not b:
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b = getattr(b, 'parent', None)
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return a is b
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def _descendant(a, b):
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# type: (PredContext, PredContext) -> PredContext
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"""
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If a is a parent of b or b is a parent of a, return the descendant of the
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two.
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If neiher is a parent of the other, return None.
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"""
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if _is_parent(a, b):
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return b
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if _is_parent(b, a):
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return a
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return None
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class Predicate(object):
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"""
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Superclass for all computed predicates.
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Leaf predicates can have other types, such as `Setting`.
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:param parts: Tuple of components in the predicate expression.
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"""
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def __init__(self, parts):
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# type: (Sequence[PredNode]) -> None
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self.name = None # type: str
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self.number = None # type: int
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self.parts = parts
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self.context = reduce(
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_descendant,
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(p.predicate_context() for p in parts))
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assert self.context, "Incompatible predicate parts"
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def __str__(self):
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# type: () -> str
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if self.name:
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return '{}.{}'.format(self.context.name, self.name)
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else:
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return '{}({})'.format(
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type(self).__name__,
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', '.join(map(str, self.parts)))
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def predicate_context(self):
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# type: () -> PredContext
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return self.context
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def predicate_leafs(self, leafs):
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# type: (Set[PredLeaf]) -> None
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"""
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Collect all leaf predicates into the `leafs` set.
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"""
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for part in self.parts:
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part.predicate_leafs(leafs)
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def rust_predicate(self, prec):
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# type: (int) -> str
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raise NotImplementedError("rust_predicate is an abstract method")
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class And(Predicate):
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"""
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Computed predicate that is true if all parts are true.
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"""
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precedence = 2
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def __init__(self, *args):
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# type: (*PredNode) -> None
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super(And, self).__init__(args)
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def rust_predicate(self, prec):
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# type: (int) -> str
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"""
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Return a Rust expression computing the value of this predicate.
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The surrounding precedence determines whether parentheses are needed:
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0. An `if` statement.
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1. An `||` expression.
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2. An `&&` expression.
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3. A `!` expression.
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"""
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s = ' && '.join(p.rust_predicate(And.precedence) for p in self.parts)
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if prec > And.precedence:
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s = '({})'.format(s)
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return s
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@staticmethod
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def combine(*args):
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# type: (*PredNode) -> PredNode
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"""
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Combine a sequence of predicates, allowing for `None` members.
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Return a predicate that is true when all non-`None` arguments are true,
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or `None` if all of the arguments are `None`.
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"""
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args = tuple(p for p in args if p)
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if args == ():
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return None
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if len(args) == 1:
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return args[0]
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# We have multiple predicate args. Combine with `And`.
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return And(*args)
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class Or(Predicate):
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"""
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Computed predicate that is true if any parts are true.
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"""
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precedence = 1
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def __init__(self, *args):
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# type: (*PredNode) -> None
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super(Or, self).__init__(args)
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def rust_predicate(self, prec):
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# type: (int) -> str
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s = ' || '.join(p.rust_predicate(Or.precedence) for p in self.parts)
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if prec > Or.precedence:
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s = '({})'.format(s)
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return s
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class Not(Predicate):
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"""
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Computed predicate that is true if its single part is false.
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"""
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precedence = 3
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def __init__(self, part):
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# type: (PredNode) -> None
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super(Not, self).__init__((part,))
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def rust_predicate(self, prec):
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# type: (int) -> str
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return '!' + self.parts[0].rust_predicate(Not.precedence)
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class FieldPredicate(object):
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"""
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An instruction predicate that performs a test on a single `FormatField`.
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:param field: The `FormatField` to be tested.
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:param function: Boolean predicate function to call.
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:param args: Additional arguments for the predicate function.
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"""
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def __init__(self, field, function, args):
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# type: (FormatField, str, Sequence[Any]) -> None
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self.number = None # type: int
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self.field = field
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self.function = function
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self.args = args
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# All PredNode members must have a name field. This will never be set.
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self.name = None # type: str
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def __str__(self):
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# type: () -> str
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args = (self.field.rust_name(),) + tuple(map(str, self.args))
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return '{}({})'.format(self.function, ', '.join(args))
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def predicate_context(self):
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# type: () -> PredContext
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"""
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This predicate can be evaluated in the context of an instruction
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format.
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"""
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return self.field.format
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def predicate_leafs(self, leafs):
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# type: (Set[PredLeaf]) -> None
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leafs.add(self)
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def rust_predicate(self, prec):
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# type: (int) -> str
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"""
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Return a string of Rust code that evaluates this predicate.
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"""
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# Prepend `field` to the predicate function arguments.
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args = (self.field.rust_name(),) + tuple(map(str, self.args))
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return 'predicates::{}({})'.format(self.function, ', '.join(args))
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class IsEqual(FieldPredicate):
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"""
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Instruction predicate that checks if an immediate instruction format field
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is equal to a constant value.
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:param field: `FormatField` to be checked.
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:param value: The constant value to compare against.
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"""
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def __init__(self, field, value):
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# type: (FormatField, Any) -> None
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super(IsEqual, self).__init__(field, 'is_equal', (value,))
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self.value = value
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class IsSignedInt(FieldPredicate):
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"""
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Instruction predicate that checks if an immediate instruction format field
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is representable as an n-bit two's complement integer.
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:param field: `FormatField` to be checked.
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:param width: Number of bits in the allowed range.
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:param scale: Number of low bits that must be 0.
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The predicate is true if the field is in the range:
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`-2^(width-1) -- 2^(width-1)-1`
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and a multiple of `2^scale`.
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"""
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def __init__(self, field, width, scale=0):
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# type: (FormatField, int, int) -> None
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super(IsSignedInt, self).__init__(
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field, 'is_signed_int', (width, scale))
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self.width = width
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self.scale = scale
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assert width >= 0 and width <= 64
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assert scale >= 0 and scale < width
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class IsUnsignedInt(FieldPredicate):
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"""
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Instruction predicate that checks if an immediate instruction format field
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is representable as an n-bit unsigned complement integer.
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:param field: `FormatField` to be checked.
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:param width: Number of bits in the allowed range.
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:param scale: Number of low bits that must be 0.
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The predicate is true if the field is in the range:
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`0 -- 2^width - 1` and a multiple of `2^scale`.
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"""
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def __init__(self, field, width, scale=0):
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# type: (FormatField, int, int) -> None
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super(IsUnsignedInt, self).__init__(
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field, 'is_unsigned_int', (width, scale))
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self.width = width
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self.scale = scale
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assert width >= 0 and width <= 64
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assert scale >= 0 and scale < width
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