minormax2code_trans.py

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# Authors: R. W. Ford and N. Nobre, STFC Daresbury Lab
# Modified: S. Siso, STFC Daresbury Lab
# Modified: A. B. G. Chalk, STFC Daresbury Lab

'''Module containing a class that provides functionality to transform
a PSyIR MIN or MAX intrinsics to PSyIR code. This could be useful if the
intrinsic is not supported by the back-end or if the performance of the
inline code is better than the intrinsic. This utility transformation
should not be called directly by the user, rather it provides
functionality that can be specialised by MIN and MAX-specific
transformations.

'''
from abc import ABC
import warnings

from psyclone.psyir.nodes import (
    BinaryOperation, Assignment, Reference, IfBlock
)
from psyclone.psyir.symbols import DataSymbol
from psyclone.psyir.transformations.intrinsics.intrinsic2code_trans import (
    Intrinsic2CodeTrans
)
from psyclone.utils import transformation_documentation_wrapper


@transformation_documentation_wrapper
class MinOrMax2CodeTrans(Intrinsic2CodeTrans, ABC):
    '''Provides a utility transformation from a PSyIR MIN or MAX Intrinsic
    node to equivalent code in a PSyIR tree. Validity checks are also
    performed (by the parent class). This utility transformation is
    not designed to be called directly by the user, rather it should
    be specialised to provide MIN or MAX transformations.

    The transformation replaces

    .. code-block:: python

        R = [MIN or MAX](A, B, C ...)

    with the following logic:

    .. code-block:: python

        R = A
        if B [< or >] R:
            R = B
        if C [< or >] R:
            R = C
        ...

    '''
    def __init__(self):
        super().__init__()
        self._compare_operator = None

    def validate(self, node, options=None):
        '''
        Check that it is safe to apply the transformation to the supplied node.

        :param node: the SIGN call to transform.
        :type node: :py:class:`psyclone.psyir.nodes.IntrinsicCall`
        :param options: any of options for the transformation.
        :type options: dict[str, Any]

        '''
        super().validate(node, options=options)
        super()._validate_scalar_arg(node)

    def apply(self, node, options=None, **kwargs):
        '''Apply this utility transformation to the specified node. This node
        must be a MIN or MAX IntrinsicCall. The intrinsic is converted to
        equivalent inline code. This is implemented as a PSyIR transform from:

        .. code-block:: python

            R = ... [MIN or MAX](A, B, C ...) ...

        to:

        .. code-block:: python

            res = A
            tmp = B
            IF tmp [< or >] res:
                res = tmp
            tmp = C
            IF tmp [< or >] res:
                res = tmp
            ...
            R = ... res ...

        where ``A``, ``B``, ``C`` ... could be arbitrarily complex
        PSyIR expressions and the ``...`` before and after ``[MIN or
        MAX](A, B, C ...)`` can be arbitrary PSyIR code.

        This transformation requires the IntrinsicCall node to be a
        descendant of an assignment and will raise an exception if
        this is not the case.

        :param node: a MIN or MAX intrinsic.
        :type node: :py:class:`psyclone.psyir.nodes.IntrinsicCall`
        :param options: a dictionary with options for transformations.
        :type options: Optional[Dict[str, Any]]

        '''
        # TODO 2668: options are now deprecated:
        if options:
            warnings.warn(self._deprecation_warning, DeprecationWarning, 2)

        # pylint: disable=too-many-locals
        self.validate(node, options, **kwargs)

        symbol_table = node.scope.symbol_table
        assignment = node.ancestor(Assignment)

        # Create two temporary variables.
        result_type = node.arguments[0].datatype
        res_var_symbol = symbol_table.new_symbol(
            f"res_{self._intrinsic.name.lower()}",
            symbol_type=DataSymbol, datatype=result_type)
        tmp_var_symbol = symbol_table.new_symbol(
            f"tmp_{self._intrinsic.name.lower()}",
            symbol_type=DataSymbol, datatype=result_type)

        # Replace intrinsic with a temporary (res_var).
        node.replace_with(Reference(res_var_symbol))

        # res_var=A (child[0] of node)
        lhs = Reference(res_var_symbol)
        new_assignment = Assignment.create(lhs, node.arguments[0].detach())
        assignment.parent.children.insert(assignment.position, new_assignment)

        # For each of the remaining arguments (B,C...)
        for expression in node.pop_all_children()[1:]:

            # tmp_var=(B or C or ...)
            lhs = Reference(tmp_var_symbol)
            new_assignment = Assignment.create(lhs, expression)
            assignment.parent.children.insert(assignment.position,
                                              new_assignment)

            # if_condition: tmp_var [< or >] res_var
            lhs = Reference(tmp_var_symbol)
            rhs = Reference(res_var_symbol)
            if_condition = BinaryOperation.create(
                self._compare_operator, lhs, rhs)

            # then_body: res_var=tmp_var
            lhs = Reference(res_var_symbol)
            rhs = Reference(tmp_var_symbol)
            then_body = [Assignment.create(lhs, rhs)]

            # if [if_condition] then [then_body]
            if_stmt = IfBlock.create(if_condition, then_body)
            assignment.parent.children.insert(assignment.position, if_stmt)


# For AutoAPI auto-documentation generation.
__all__ = ["MinOrMax2CodeTrans"]