bf1568035f
Each instruction used in a pattern has constraints on the types of its operands. These constraints are expressed as symbolic type variables. Compute type variables for each variable used in a transformation pattern. Some are free type variables, and some are derived from the free type variables. The type variables associated with variables can be used for computing the result types of replacement instructions that don't support simple forward type inference from their inputs. The type sets computed by this patch are conservatively too large, so they can't yet be used to type check patterns.
288 lines
9.7 KiB
Python
288 lines
9.7 KiB
Python
"""
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Instruction transformations.
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"""
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from __future__ import absolute_import
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from .ast import Def, Var, Apply
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try:
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from typing import Union, Iterator, Sequence, Iterable # noqa
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from .ast import Expr # noqa
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DefApply = Union[Def, Apply]
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except ImportError:
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pass
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def canonicalize_defapply(node):
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# type: (DefApply) -> Def
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"""
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Canonicalize a `Def` or `Apply` node into a `Def`.
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An `Apply` becomes a `Def` with an empty list of defs.
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"""
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if isinstance(node, Apply):
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return Def((), node)
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else:
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return node
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class Rtl(object):
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"""
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Register Transfer Language list.
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An RTL object contains a list of register assignments in the form of `Def`
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objects.
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An RTL list can represent both a source pattern to be matched, or a
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destination pattern to be inserted.
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"""
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def __init__(self, *args):
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# type: (*DefApply) -> None
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self.rtl = tuple(map(canonicalize_defapply, args))
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def __iter__(self):
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# type: () -> Iterator[Def]
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return iter(self.rtl)
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class XForm(object):
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"""
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An instruction transformation consists of a source and destination pattern.
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Patterns are expressed in *register transfer language* as tuples of
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`ast.Def` or `ast.Expr` nodes.
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A legalization pattern must have a source pattern containing only a single
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instruction.
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>>> from base.instructions import iconst, iadd, iadd_imm
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>>> a = Var('a')
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>>> c = Var('c')
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>>> v = Var('v')
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>>> x = Var('x')
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>>> XForm(
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... Rtl(c << iconst(v),
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... a << iadd(x, c)),
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... Rtl(a << iadd_imm(x, v)))
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XForm(inputs=[Var(v), Var(x)], defs=[Var(c, src), Var(a, src, dst)],
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c << iconst(v)
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a << iadd(x, c)
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=>
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a << iadd_imm(x, v)
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)
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"""
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def __init__(self, src, dst):
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# type: (Rtl, Rtl) -> None
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self.src = src
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self.dst = dst
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# Variables that are inputs to the source pattern.
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self.inputs = list() # type: List[Var]
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# Variables defined in either src or dst.
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self.defs = list() # type: List[Var]
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# Rewrite variables in src and dst RTL lists to our own copies.
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# Map name -> private Var.
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symtab = dict() # type: Dict[str, Var]
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self._rewrite_rtl(src, symtab, Var.SRCCTX)
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num_src_inputs = len(self.inputs)
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self._rewrite_rtl(dst, symtab, Var.DSTCTX)
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# Check for inconsistently used inputs.
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for i in self.inputs:
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if not i.is_input():
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raise AssertionError(
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"'{}' used as both input and def".format(i))
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# Check for spurious inputs in dst.
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if len(self.inputs) > num_src_inputs:
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raise AssertionError(
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"extra inputs in dst RTL: {}".format(
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self.inputs[num_src_inputs:]))
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self._infer_types(self.src)
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self._infer_types(self.dst)
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self._collect_typevars()
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def __repr__(self):
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s = "XForm(inputs={}, defs={},\n ".format(self.inputs, self.defs)
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s += '\n '.join(str(n) for n in self.src)
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s += '\n=>\n '
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s += '\n '.join(str(n) for n in self.dst)
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s += '\n)'
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return s
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def _rewrite_rtl(self, rtl, symtab, context):
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# type: (Rtl, Dict[str, Var], int) -> None
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for line in rtl.rtl:
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if isinstance(line, Def):
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line.defs = tuple(
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self._rewrite_defs(line, symtab, context))
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expr = line.expr
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else:
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expr = line
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self._rewrite_expr(expr, symtab, context)
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def _rewrite_expr(self, expr, symtab, context):
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# type: (Apply, Dict[str, Var], int) -> None
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"""
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Find all uses of variables in `expr` and replace them with our own
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local symbols.
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"""
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# Accept a whole expression tree.
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stack = [expr]
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while len(stack) > 0:
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expr = stack.pop()
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expr.args = tuple(
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self._rewrite_uses(expr, stack, symtab, context))
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def _rewrite_defs(self, line, symtab, context):
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# type: (Def, Dict[str, Var], int) -> Iterable[Var]
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"""
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Given a tuple of symbols defined in a Def, rewrite them to local
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symbols. Yield the new locals.
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"""
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for sym in line.defs:
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name = str(sym)
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if name in symtab:
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var = symtab[name]
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if var.get_def(context):
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raise AssertionError("'{}' multiply defined".format(name))
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else:
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var = Var(name)
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symtab[name] = var
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self.defs.append(var)
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var.set_def(context, line)
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yield var
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def _rewrite_uses(self, expr, stack, symtab, context):
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# type: (Apply, List[Apply], Dict[str, Var], int) -> Iterable[Expr]
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"""
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Given an `Apply` expr, rewrite all uses in its arguments to local
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variables. Yield a sequence of new arguments.
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Append any `Apply` arguments to `stack`.
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"""
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for arg, operand in zip(expr.args, expr.inst.ins):
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# Nested instructions are allowed. Visit recursively.
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if isinstance(arg, Apply):
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stack.append(arg)
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yield arg
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continue
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if not isinstance(arg, Var):
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assert not operand.is_value(), "Value arg must be `Var`"
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yield arg
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continue
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# This is supposed to be a symbolic value reference.
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name = str(arg)
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if name in symtab:
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var = symtab[name]
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# The variable must be used consistently as a def or input.
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if not var.is_input() and not var.get_def(context):
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raise AssertionError(
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"'{}' used as both input and def"
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.format(name))
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else:
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# First time use of variable.
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var = Var(name)
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symtab[name] = var
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self.inputs.append(var)
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yield var
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def verify_legalize(self):
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# type: () -> None
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"""
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Verify that this is a valid legalization XForm.
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- The source pattern must describe a single instruction.
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- All values defined in the output pattern must be defined in the
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destination pattern.
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"""
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assert len(self.src.rtl) == 1, "Legalize needs single instruction."
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for d in self.src.rtl[0].defs:
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if not d.is_output():
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raise AssertionError(
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'{} not defined in dest pattern'.format(d))
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def _infer_types(self, rtl):
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# type: (Rtl) -> None
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"""Assign type variables to all value variables used in `rtl`."""
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for d in rtl.rtl:
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inst = d.expr.inst
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# Get the Var corresponding to the controlling type variable.
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ctrl_var = None # type: Var
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if inst.is_polymorphic:
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if inst.use_typevar_operand:
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# Should this be an assertion instead?
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# Should all value operands be required to be Vars?
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arg = d.expr.args[inst.format.typevar_operand]
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if isinstance(arg, Var):
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ctrl_var = arg
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else:
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ctrl_var = d.defs[inst.value_results[0]]
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# Reconcile arguments with the requirements of `inst`.
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for opnum in inst.format.value_operands:
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inst_tv = inst.ins[opnum].typevar
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v = d.expr.args[opnum]
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if isinstance(v, Var):
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v.constrain_typevar(inst_tv, inst.ctrl_typevar, ctrl_var)
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# Reconcile results with the requirements of `inst`.
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for resnum in inst.value_results:
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inst_tv = inst.outs[resnum].typevar
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v = d.defs[resnum]
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v.constrain_typevar(inst_tv, inst.ctrl_typevar, ctrl_var)
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def _collect_typevars(self):
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# type: () -> None
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"""
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Collect a list of variables whose type can be used to infer the types
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of all expressions.
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This should be called after `_infer_types()` above has computed type
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variables for all the used vars.
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"""
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fvars = list(v for v in self.inputs if v.has_free_typevar())
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fvars += list(v for v in self.defs if v.has_free_typevar())
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self.free_typevars = fvars
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# When substituting a pattern, we know the types of all variables that
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# appear on the source side: inut, output, and intermediate values.
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# However, temporary values which appear only on the destination side
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# must have their type computed somehow.
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#
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# Some variables have a fixed type which appears as a type variable
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# with a singleton_type field set. That's allowed for temps too.
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for v in fvars:
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if v.is_temp() and not v.typevar.singleton_type:
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raise AssertionError(
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"Cannot determine type of temp '{}' in xform:\n{}"
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.format(v, self))
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class XFormGroup(object):
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"""
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A group of related transformations.
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"""
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def __init__(self, name, doc):
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# type: (str, str) -> None
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self.xforms = list() # type: List[XForm]
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self.name = name
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self.__doc__ = doc
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def legalize(self, src, dst):
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# type: (Union[Def, Apply], Rtl) -> None
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"""
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Add a legalization pattern to this group.
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:param src: Single `Def` or `Apply` to be legalized.
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:param dst: `Rtl` list of replacement instructions.
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"""
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xform = XForm(Rtl(src), dst)
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xform.verify_legalize()
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self.xforms.append(xform)
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