863 lines
31 KiB
ReStructuredText
863 lines
31 KiB
ReStructuredText
===================================
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TableGen Backend Developer's Guide
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===================================
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.. sectnum::
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.. contents::
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:local:
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Introduction
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============
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The purpose of TableGen is to generate complex output files based on
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information from source files that are significantly easier to code than the
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output files would be, and also easier to maintain and modify over time. The
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information is coded in a declarative style involving classes and records,
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which are then processed by TableGen. The internalized records are passed on
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to various backends, which extract information from a subset of the records
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and generate an output file. These output files are typically ``.inc`` files
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for C++, but may be any type of file that the backend developer needs.
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This document is a guide to writing a backend for TableGen. It is not a
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complete reference manual, but rather a guide to using the facilities
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provided by TableGen for the backends. For a complete reference to the
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various data structures and functions involved, see the primary TableGen
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header file (``record.h``) and/or the Doxygen documentation.
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This document assumes that you have read the :doc:`TableGen Programmer's
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Reference <./ProgRef>`, which provides a detailed reference for coding
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TableGen source files. For a description of the existing backends, see
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:doc:`TableGen BackEnds <./BackEnds>`.
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Data Structures
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===============
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The following sections describe the data structures that contain the classes
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and records that are collected from the TableGen source files by the
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TableGen parser. Note that the term *class* refers to an abstract record
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class, while the term *record* refers to a concrete record.
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Unless otherwise noted, functions associated with classes are instance
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functions.
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``RecordKeeper``
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----------------
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An instance of the ``RecordKeeper`` class acts as the container for all the
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classes and records parsed and collected by TableGen. The ``RecordKeeper``
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instance is passed to the backend when it is invoked by TableGen. This class
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is usually abbreviated ``RK``.
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There are two maps in the recordkeeper, one for classes and one for records
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(the latter often referred to as *defs*). Each map maps the class or record
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name to an instance of the ``Record`` class (see `Record`_), which contains
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all the information about that class or record.
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In addition to the two maps, the ``RecordKeeper`` instance contains:
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* A map that maps the names of global variables to their values.
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Global variables are defined in TableGen files with outer
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``defvar`` statements.
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* A counter for naming anonymous records.
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The ``RecordKeeper`` class provides a few useful functions.
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* Functions to get the complete class and record maps.
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* Functions to get a subset of the records based on their parent classes.
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* Functions to get individual classes, records, and globals, by name.
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A ``RecordKeeper`` instance can be printed to an output stream with the ``<<``
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operator.
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``Record``
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----------
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Each class or record built by TableGen is represented by an instance of
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the ``Record`` class. The ``RecordKeeper`` instance contains one map for the
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classes and one for the records. The primary data members of a record are
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the record name, the vector of field names and their values, and the vector of
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superclasses of the record.
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The record name is stored as a pointer to an ``Init`` (see `Init`_), which
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is a class whose instances hold TableGen values (sometimes referred to as
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*initializers*). The field names and values are stored in a vector of
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``RecordVal`` instances (see `RecordVal`_), each of which contains both the
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field name and its value. The superclass vector contains a sequence of
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pairs, with each pair including the superclass record and its source
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file location.
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In addition to those members, a ``Record`` instance contains:
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* A vector of source file locations that includes the record definition
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itself, plus the locations of any multiclasses involved in its definition.
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* For a class record, a vector of the class's template arguments.
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* An instance of ``DefInit`` (see `DefInit`_) corresponding to this record.
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* A unique record ID.
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* A boolean that specifies whether this is a class definition.
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* A boolean that specifies whether this is an anonymous record.
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The ``Record`` class provides many useful functions.
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* Functions to get the record name, fields, source file locations,
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template arguments, and unique ID.
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* Functions to get all the record's superclasses or just its direct
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superclasses.
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* Functions to get a particular field value by specifying its name in various
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forms, and returning its value in various forms
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(see `Getting Record Names and Fields`_).
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* Boolean functions to check the various attributes of the record.
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A ``Record`` instance can be printed to an output stream with the ``<<``
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operator.
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``RecordVal``
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-------------
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Each field of a record is stored in an instance of the ``RecordVal`` class.
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The ``Record`` instance includes a vector of these value instances. A
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``RecordVal`` instance contains the name of the field, stored in an ``Init``
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instance. It also contains the value of the field, likewise stored in an
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``Init``. (A better name for this class might be ``RecordField``.)
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In addition to those primary members, the ``RecordVal`` has other data members.
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* The source file location of the field definition.
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* The type of the field, stored as an instance
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of the ``RecTy`` class (see `RecTy`_).
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The ``RecordVal`` class provides some useful functions.
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* Functions to get the name of the field in various forms.
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* A function to get the type of the field.
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* A function to get the value of the field.
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* A function to get the source file location.
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Note that field values are more easily obtained directly from the ``Record``
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instance (see `Record`_).
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A ``RecordVal`` instance can be printed to an output stream with the ``<<``
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operator.
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``RecTy``
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---------
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The ``RecTy`` class is used to represent the types of field values. It is
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the base class for a series of subclasses, one for each of the
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available field types. The ``RecTy`` class has one data member that is an
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enumerated type specifying the specific type of field value. (A better
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name for this class might be ``FieldTy``.)
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The ``RecTy`` class provides a few useful functions.
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* A virtual function to get the type name as a string.
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* A virtual function to check whether all the values of this type can
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be converted to another given type.
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* A virtual function to check whether this type is a subtype of
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another given type.
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* A function to get the corresponding ``list``
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type for lists with elements of this type. For example, the function
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returns the ``list<int>`` type when called with the ``int`` type.
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The subclasses that inherit from ``RecTy`` are
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``BitRecTy``,
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``BitsRecTy``,
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``CodeRecTy``,
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``DagRecTy``,
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``IntRecTy``,
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``ListRecTy``,
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``RecordRecTy``, and
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``StringRecTy``.
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Some of these classes have additional members that
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are described in the following subsections.
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*All* of the classes derived from ``RecTy`` provide the ``get()`` function.
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It returns an instance of ``Recty`` corresponding to the derived class.
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Some of the ``get()`` functions require an argument to
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specify which particular variant of the type is desired. These arguments are
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described in the following subsections.
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A ``RecTy`` instance can be printed to an output stream with the ``<<``
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operator.
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.. warning::
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It is not specified whether there is a single ``RecTy`` instance of a
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particular type or multiple instances.
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``BitsRecTy``
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~~~~~~~~~~~~~
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This class includes a data member with the size of the ``bits`` value and a
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function to get that size.
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The ``get()`` function takes the length of the sequence, *n*, and returns the
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``BitsRecTy`` type corresponding to ``bits<``\ *n*\ ``>``.
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``ListRecTy``
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~~~~~~~~~~~~~
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This class includes a data member that specifies the type of the list's
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elements and a function to get that type.
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The ``get()`` function takes the ``RecTy`` *type* of the list members and
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returns the ``ListRecTy`` type corresponding to ``list<``\ *type*\ ``>``.
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``RecordRecTy``
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~~~~~~~~~~~~~~~
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This class includes data members that contain the list of parent classes of
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this record. It also provides a function to obtain the array of classes and
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two functions to get the iterator ``begin()`` and ``end()`` values. The
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class defines a type for the return values of the latter two functions.
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.. code-block:: text
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using const_record_iterator = Record * const *;
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The ``get()`` function takes an ``ArrayRef`` of pointers to the ``Record``
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instances of the *direct* superclasses of the record and returns the ``RecordRecTy``
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corresponding to the record inheriting from those superclasses.
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``Init``
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--------
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The ``Init`` class is used to represent TableGen values. The name derives
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from *initialization value*. This class should not be confused with the
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``RecordVal`` class, which represents record fields, both their names and
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values. The ``Init`` class is the base class for a series of subclasses, one
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for each of the available value types. The primary data member of ``Init``
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is an enumerated type that represents the specific type of the value.
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The ``Init`` class provides a few useful functions.
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* A function to get the type enumerator.
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* A boolean virtual function to determine whether a value is completely
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specified; that is, has no uninitialized subvalues.
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* Virtual functions to get the value as a string.
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* Virtual functions to cast the value to other types, implement the bit
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range feature of TableGen, and implement the list slice feature.
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* A virtual function to get a particular bit of the value.
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The subclasses that inherit directly from ``Init`` are
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``UnsetInit`` and ``TypedInit``.
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An ``Init`` instance can be printed to an output stream with the ``<<``
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operator.
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.. warning::
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It is not specified whether two separate initialization values with
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the same underlying type and value (e.g., two strings with the value
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"Hello") are represented by two ``Init``\ s or share the same ``Init``.
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``UnsetInit``
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~~~~~~~~~~~~~
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This class, a subclass of ``Init``, represents the unset (uninitialized)
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value. The static function ``get()`` can be used to obtain the singleton
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``Init`` of this type.
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``TypedInit``
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~~~~~~~~~~~~~
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This class, a subclass of ``Init``, acts as the parent class of the classes
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that represent specific value types (except for the unset value). These
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classes include ``BitInit``, ``BitsInit``, ``DagInit``, ``DefInit``,
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``IntInit``, ``ListInit``, and ``StringInit``. (There are additional derived
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types used by the TableGen parser.)
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This class includes a data member that specifies the ``RecTy`` type of the
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value. It provides a function to get that ``RecTy`` type.
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``BitInit``
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~~~~~~~~~~~
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The ``BitInit`` class is a subclass of ``TypedInit``. Its instances
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represent the possible values of a bit: 0 or 1. It includes a data member
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that contains the bit.
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*All* of the classes derived from ``TypedInit`` provide the following functions.
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* A static function named ``get()`` that returns an ``Init`` representing
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the specified value(s). In the case of ``BitInit``, ``get(true)`` returns
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an instance of ``BitInit`` representing true, while ``get(false)`` returns
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an instance
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representing false. As noted above, it is not specified whether there
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is exactly one or more than one ``BitInit`` representing true (or false).
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* A function named ``GetValue()`` that returns the value of the instance
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in a more direct form, in this case as a ``bool``.
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``BitsInit``
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~~~~~~~~~~~~
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The ``BitsInit`` class is a subclass of ``TypedInit``. Its instances
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represent sequences of bits, from high-order to low-order. It includes a
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data member with the length of the sequence and a vector of pointers to
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``Init`` instances, one per bit.
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The class provides the usual ``get()`` function. It does not provide the
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``getValue()`` function.
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The class provides the following additional functions.
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* A function to get the number of bits in the sequence.
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* A function that gets a bit specified by an integer index.
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``DagInit``
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~~~~~~~~~~~
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The ``DagInit`` class is a subclass of ``TypedInit``. Its instances
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represent the possible direct acyclic graphs (``dag``).
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The class includes a pointer to an ``Init`` for the DAG operator and a
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pointer to a ``StringInit`` for the operator name. It includes the count of
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DAG operands and the count of operand names. Finally, it includes a vector of
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pointers to ``Init`` instances for the operands and another to
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``StringInit`` instances for the operand names.
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(The DAG operands are also referred to as *arguments*.)
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The class provides two forms of the usual ``get()`` function. It does not
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provide the usual ``getValue()`` function.
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The class provides many additional functions:
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* Functions to get the operator in various forms and to get the
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operator name in various forms.
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* Functions to determine whether there are any operands and to get the
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number of operands.
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* Functions to the get the operands, both individually and together.
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* Functions to determine whether there are any names and to
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get the number of names
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* Functions to the get the names, both individually and together.
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* Functions to get the operand iterator ``begin()`` and ``end()`` values.
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* Functions to get the name iterator ``begin()`` and ``end()`` values.
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The class defines two types for the return values of the operand and name
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iterators.
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.. code-block:: text
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using const_arg_iterator = SmallVectorImpl<Init*>::const_iterator;
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using const_name_iterator = SmallVectorImpl<StringInit*>::const_iterator;
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``DefInit``
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~~~~~~~~~~~
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The ``DefInit`` class is a subclass of ``TypedInit``. Its instances
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represent the records that were collected by TableGen. It includes a data
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member that is a pointer to the record's ``Record`` instance.
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The class provides the usual ``get()`` function. It does not provide
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``getValue()``. Instead, it provides ``getDef()``, which returns the
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``Record`` instance.
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``IntInit``
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~~~~~~~~~~~
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The ``IntInit`` class is a subclass of ``TypedInit``. Its instances
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represent the possible values of a 64-bit integer. It includes a data member
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that contains the integer.
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The class provides the usual ``get()`` and ``getValue()`` functions. The
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latter function returns the integer as an ``int64_t``.
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The class also provides a function, ``getBit()``, to obtain a specified bit
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of the integer value.
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``ListInit``
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~~~~~~~~~~~~
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The ``ListInit`` class is a subclass of ``TypedInit``. Its instances
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represent lists of elements of some type. It includes a data member with the
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length of the list and a vector of pointers to ``Init`` instances, one per
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element.
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The class provides the usual ``get()`` and ``getValues()`` functions. The
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latter function returns an ``ArrayRef`` of the vector of pointers to ``Init``
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instances.
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The class provides these additional functions.
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* A function to get the element type.
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* Functions to get the length of the vector and to determine whether
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it is empty.
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* Functions to get an element specified by an integer index and return
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it in various forms.
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* Functions to get the iterator ``begin()`` and ``end()`` values. The
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class defines a type for the return type of these two functions.
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.. code-block:: text
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using const_iterator = Init *const *;
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``StringInit``
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~~~~~~~~~~~~~~
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The ``StringInit`` class is a subclass of ``TypedInit``. Its instances
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represent arbitrary-length strings. It includes a data member
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that contains a ``StringRef`` of the value.
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The class provides the usual ``get()`` and ``getValue()`` functions. The
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latter function returns the ``StringRef``.
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Creating a New Backend
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======================
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The following steps are required to create a new backend for TableGen.
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#. Invent a name for your backend C++ file, say ``GenAddressModes``.
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#. Write the new backend, using the file ``TableGenBackendSkeleton.cpp``
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as a starting point.
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#. Determine which instance of TableGen requires the new backend. There is
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one instance for Clang and another for LLVM. Or you may be building
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your own instance.
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#. Modify the selected ``tablegen.cpp`` to include your new backend.
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a. Add the name to the enumerated type ``ActionType``.
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#. Add a keyword to the ``ActionType`` command option using the
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``clEnumValN()`` function.
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#. Add a case to the ``switch`` statement in the *xxx*\ ``TableGenMain()``
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function. It should invoke the "main function" of your backend, which
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in this case, according to convention, is named ``EmitAddressModes``.
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5. Add a declaration of your "main function" to the corresponding
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``TableGenBackends.h`` header file.
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#. Add your backend C++ file to the appropriate ``CMakeLists.txt`` file so
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that it will be built.
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#. Add your C++ file to the system.
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The Backend Skeleton
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====================
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The file ``TableGenBackendSkeleton.cpp`` provides a skeleton C++ translation
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unit for writing a new TableGen backend. Here are a few notes on the file.
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* The list of includes is the minimal list required by most backends.
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* As with all LLVM C++ files, it has a ``using namespace llvm;`` statement.
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It also has an anonymous namespace that contains all the file-specific
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data structure definitions, along with the class embodying the emitter
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data members and functions. Continuing with the ``GenAddressModes`` example,
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this class is named ``AddressModesEmitter``.
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* The constructor for the emitter class accepts a ``RecordKeeper`` reference,
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typically named ``RK``. The ``RecordKeeper`` reference is saved in a data
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member so that records can be obtained from it. This data member is usually
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named ``Records``.
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* One function is named ``run``. It is invoked by the backend's "main
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function" to collect records and emit the output file. It accepts an instance
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of the ``raw_ostream`` class, typically named ``OS``. The output file is
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emitted by writing to this stream.
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* The ``run`` function should use the ``emitSourceFileHeader`` helper function
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to include a standard header in the emitted file.
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* The only function in the ``llvm`` namespace is the backend "main function."
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In this example, it is named ``EmitAddressModes``. It creates an instance
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of the ``AddressModesEmitter`` class, passing the ``RecordKeeper``
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instance, then invokes the ``run`` function, passing the ``raw_ostream``
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instance.
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All the examples in the remainder of this document will assume the naming
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conventions used in the skeleton file.
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Getting Classes
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===============
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The ``RecordKeeper`` class provides two functions for getting the
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``Record`` instances for classes defined in the TableGen files.
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* ``getClasses()`` returns a ``RecordMap`` reference for all the classes.
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* ``getClass(``\ *name*\ ``)`` returns a ``Record`` reference for the named
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class.
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If you need to iterate over all the class records:
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.. code-block:: text
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for (auto ClassPair : Records.getClasses()) {
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Record *ClassRec = ClassPair.second.get();
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...
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}
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``ClassPair.second`` gets the class's ``unique_ptr``, then ``.get()`` gets the
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class ``Record`` itself.
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Getting Records
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===============
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The ``RecordKeeper`` class provides four functions for getting the
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``Record`` instances for concrete records defined in the TableGen files.
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* ``getDefs()`` returns a ``RecordMap`` reference for all the concrete
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records.
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* ``getDef(``\ *name*\ ``)`` returns a ``Record`` reference for the named
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concrete record.
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* ``getAllDerivedDefinitions(``\ *classname*\ ``)`` returns a vector of
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``Record`` references for the concrete records that derive from the
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given class.
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* ``getAllDerivedDefinitions(``\ *classnames*\ ``)`` returns
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a vector of ``Record`` references for the concrete records that derive from
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*all* of the given classes.
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This statement obtains all the records that derive from the ``Attribute``
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class and iterates over them.
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.. code-block:: text
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auto AttrRecords = Records.getAllDerivedDefinitions("Attribute");
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for (Record *AttrRec : AttrRecords) {
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...
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}
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Getting Record Names and Fields
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===============================
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As described above (see `Record`_), there are multiple functions that
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return the name of a record. One particularly useful one is
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``getNameInitAsString()``, which returns the name as a ``std::string``.
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There are also multiple functions that return the fields of a record. To
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obtain and iterate over all the fields:
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.. code-block:: text
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for (const RecordVal &Field : SomeRec->getValues()) {
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...
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}
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You will recall that ``RecordVal`` is the class whose instances contain
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information about the fields in records.
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The ``getValue()`` function returns the ``RecordVal`` instance for a field
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specified by name. There are multiple overloaded functions, some taking a
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``StringRef`` and others taking a ``const Init *``. Some functions return a
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``RecordVal *`` and others return a ``const RecordVal *``. If the field does
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not exist, a fatal error message is printed.
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More often than not, you are interested in the value of the field, not all
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the information in the ``RecordVal``. There is a large set of functions that
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take a field name in some form and return its value. One function,
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``getValueInit``, returns the value as an ``Init *``. Another function,
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``isValueUnset``, returns a boolean specifying whether the value is unset
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(uninitialized).
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Most of the functions return the value in some more useful form. For
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example:
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.. code-block:: text
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std::vector<int64_t> RegCosts =
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SomeRec->getValueAsListOfInts("RegCosts");
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The field ``RegCosts`` is assumed to be a list of integers. That list is
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returned as a ``std::vector`` of 64-bit integers. If the field is not a list
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of integers, a fatal error message is printed.
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Here is a function that returns a field value as a ``Record``, but returns
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null if the field does not exist.
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.. code-block:: text
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if (Record *BaseRec = SomeRec->getValueAsOptionalDef(BaseFieldName)) {
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...
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}
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The field is assumed to have another record as its value. That record is returned
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as a pointer to a ``Record``. If the field does not exist or is unset, the
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functions returns null.
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Getting Record Superclasses
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===========================
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The ``Record`` class provides a function to obtain the superclasses of a
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record. It is named ``getSuperClasses`` and returns an ``ArrayRef`` of an
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array of ``std::pair`` pairs. The superclasses are in post-order: the order
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in which the superclasses were visited while copying their fields into the
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record. Each pair consists of a pointer to the ``Record`` instance for a
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superclass record and an instance of the ``SMRange`` class. The range
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indicates the source file locations of the beginning and end of the class
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definition.
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This example obtains the superclasses of the ``Prototype`` record and then
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iterates over the pairs in the returned array.
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.. code-block:: text
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ArrayRef<std::pair<Record *, SMRange>>
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Superclasses = Prototype->getSuperClasses();
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for (const auto &SuperPair : Superclasses) {
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...
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}
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The ``Record`` class also provides a function, ``getDirectSuperClasses``, to
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append the *direct* superclasses of a record to a given vector of type
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``SmallVectorImpl<Record *>``.
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Emitting Text to the Output Stream
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==================================
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The ``run`` function is passed a ``raw_ostream`` to which it prints the
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output file. By convention, this stream is saved in the emitter class member
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named ``OS``, although some ``run`` functions are simple and just use the
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stream without saving it. The output can be produced by writing values
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directly to the output stream, or by using the ``std::format()`` or
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``llvm::formatv()`` functions.
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.. code-block:: text
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OS << "#ifndef " << NodeName << "\n";
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OS << format("0x%0*x, ", Digits, Value);
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Instances of the following classes can be printed using the ``<<`` operator:
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``RecordKeeper``,
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``Record``,
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``RecTy``,
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``RecordVal``, and
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``Init``.
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The helper function ``emitSourceFileHeader()`` prints the header comment
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that should be included at the top of every output file. A call to it is
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included in the skeleton backend file ``TableGenBackendSkeleton.cpp``.
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Printing Error Messages
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=======================
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TableGen records are often derived from multiple classes and also often
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defined through a sequence of multiclasses. Because of this, it can be
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difficult for backends to report clear error messages with accurate source
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file locations. To make error reporting easier, five error reporting
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functions are provided, each with four overloads.
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* ``PrintWarning`` prints a message tagged as a warning.
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* ``PrintError`` prints a message tagged as an error.
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* ``PrintFatalError`` prints a message tagged as an error and then terminates.
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* ``PrintNote`` prints a note. It is often used after one of the previous
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functions to provide more information.
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* ``PrintFatalNote`` prints a note and then terminates.
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Each of these five functions is overloaded four times.
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* ``PrintError(const Twine &Msg)``:
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Prints the message with no source file location.
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* ``PrintError(ArrayRef<SMLoc> ErrorLoc, const Twine &Msg)``:
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Prints the message followed by the specified source line,
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along with a pointer to the item in error. The array of
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source file locations is typically taken from a ``Record`` instance.
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* ``PrintError(const Record *Rec, const Twine &Msg)``:
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Prints the message followed by the source line associated with the
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specified record (see `Record`_).
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* ``PrintError(const RecordVal *RecVal, const Twine &Msg)``:
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Prints the message followed by the source line associated with the
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specified record field (see `RecordVal`_).
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Using these functions, the goal is to produce the most specific error report
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possible.
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Debugging Tools
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===============
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TableGen provides some tools to aid in debugging backends.
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The ``PrintRecords`` Backend
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----------------------------
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The TableGen command option ``--print-records`` invokes a simple backend
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that prints all the classes and records defined in the source files. This is
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the default backend option. The format of the output is guaranteed to be
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constant over time, so that the output can be compared in tests. The output
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looks like this:
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.. code-block:: text
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------------- Classes -----------------
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...
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class XEntry<string XEntry:str = ?, int XEntry:val1 = ?> { // XBase
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string Str = XEntry:str;
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bits<8> Val1 = { !cast<bits<8>>(XEntry:val1){7}, ... };
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bit Val3 = 1;
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}
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...
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------------- Defs -----------------
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def ATable { // GenericTable
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string FilterClass = "AEntry";
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string CppTypeName = "AEntry";
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list<string> Fields = ["Str", "Val1", "Val2"];
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list<string> PrimaryKey = ["Val1", "Val2"];
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string PrimaryKeyName = "lookupATableByValues";
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bit PrimaryKeyEarlyOut = 0;
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}
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...
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def anonymous_0 { // AEntry
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string Str = "Bob";
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bits<8> Val1 = { 0, 0, 0, 0, 0, 1, 0, 1 };
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bits<10> Val2 = { 0, 0, 0, 0, 0, 0, 0, 0, 1, 1 };
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}
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Classes are shown with their template arguments, parent classes (following
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``//``), and fields. Records are shown with their parent classes and
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fields. Note that anonymous records are named ``anonymous_0``,
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``anonymous_1``, etc.
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The ``PrintDetailedRecords`` Backend
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------------------------------------
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The TableGen command option ``--print-detailed-records`` invokes a backend
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that prints all the global variables, classes, and records defined in the
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source files. The format of the output is *not* guaranteed to be constant
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over time. The output looks like this.
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.. code-block:: text
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DETAILED RECORDS for file llvm-project\llvm\lib\target\arc\arc.td
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-------------------- Global Variables (5) --------------------
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AMDGPUBufferIntrinsics = [int_amdgcn_buffer_load_format, ...
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AMDGPUImageDimAtomicIntrinsics = [int_amdgcn_image_atomic_swap_1d, ...
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...
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-------------------- Classes (758) --------------------
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AMDGPUBufferLoad |IntrinsicsAMDGPU.td:879|
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Template args:
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LLVMType AMDGPUBufferLoad:data_ty = llvm_any_ty |IntrinsicsAMDGPU.td:879|
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Superclasses: (SDPatternOperator) Intrinsic AMDGPURsrcIntrinsic
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Fields:
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list<SDNodeProperty> Properties = [SDNPMemOperand] |Intrinsics.td:348|
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string LLVMName = "" |Intrinsics.td:343|
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...
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-------------------- Records (12303) --------------------
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AMDGPUSample_lz_o |IntrinsicsAMDGPU.td:560|
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Defm sequence: |IntrinsicsAMDGPU.td:584| |IntrinsicsAMDGPU.td:566|
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Superclasses: AMDGPUSampleVariant
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Fields:
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string UpperCaseMod = "_LZ_O" |IntrinsicsAMDGPU.td:542|
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string LowerCaseMod = "_lz_o" |IntrinsicsAMDGPU.td:543|
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...
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* Global variables defined with outer ``defvar`` statements are shown with
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their values.
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* The classes are shown with their source location, template arguments,
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superclasses, and fields.
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* The records are shown with their source location, ``defm`` sequence,
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superclasses, and fields.
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Superclasses are shown in the order processed, with indirect superclasses in
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parentheses. Each field is shown with its value and the source location at
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which it was set.
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The ``defm`` sequence gives the locations of the ``defm`` statements that
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were involved in generating the record, in the order they were invoked.
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Timing TableGen Phases
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----------------------
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TableGen provides a phase timing feature that produces a report of the time
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used by the various phases of parsing the source files and running the
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selected backend. This feature is enabled with the ``--time-phases`` option
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of the TableGen command.
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If the backend is *not* instrumented for timing, then a report such as the
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following is produced. This is the timing for the
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``--print-detailed-records`` backend run on the AMDGPU target.
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.. code-block:: text
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===-------------------------------------------------------------------------===
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TableGen Phase Timing
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===-------------------------------------------------------------------------===
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Total Execution Time: 101.0106 seconds (102.4819 wall clock)
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---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
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85.5197 ( 84.9%) 0.1560 ( 50.0%) 85.6757 ( 84.8%) 85.7009 ( 83.6%) Backend overall
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15.1789 ( 15.1%) 0.0000 ( 0.0%) 15.1789 ( 15.0%) 15.1829 ( 14.8%) Parse, build records
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0.0000 ( 0.0%) 0.1560 ( 50.0%) 0.1560 ( 0.2%) 1.5981 ( 1.6%) Write output
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100.6986 (100.0%) 0.3120 (100.0%) 101.0106 (100.0%) 102.4819 (100.0%) Total
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Note that all the time for the backend is lumped under "Backend overall".
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If the backend is instrumented for timing, then its processing is
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divided into phases and each one timed separately. This is the timing for
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the ``--emit-dag-isel`` backend run on the AMDGPU target.
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.. code-block:: text
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===-------------------------------------------------------------------------===
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TableGen Phase Timing
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===-------------------------------------------------------------------------===
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Total Execution Time: 746.3868 seconds (747.1447 wall clock)
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---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
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657.7938 ( 88.1%) 0.1404 ( 90.0%) 657.9342 ( 88.1%) 658.6497 ( 88.2%) Emit matcher table
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70.2317 ( 9.4%) 0.0000 ( 0.0%) 70.2317 ( 9.4%) 70.2700 ( 9.4%) Convert to matchers
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14.8825 ( 2.0%) 0.0156 ( 10.0%) 14.8981 ( 2.0%) 14.9009 ( 2.0%) Parse, build records
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2.1840 ( 0.3%) 0.0000 ( 0.0%) 2.1840 ( 0.3%) 2.1791 ( 0.3%) Sort patterns
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1.1388 ( 0.2%) 0.0000 ( 0.0%) 1.1388 ( 0.2%) 1.1401 ( 0.2%) Optimize matchers
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0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0050 ( 0.0%) Write output
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746.2308 (100.0%) 0.1560 (100.0%) 746.3868 (100.0%) 747.1447 (100.0%) Total
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The backend has been divided into four phases and timed separately.
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If you want to instrument a backend, refer to the backend ``DAGISelEmitter.cpp``
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and search for ``Records.startTimer``. |