--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/llvm/docs/TableGen/BackGuide.rst	Tue Jun 08 06:07:14 2021 +0900
@@ -0,0 +1,863 @@
+===================================
+TableGen Backend Developer's Guide
+===================================
+
+.. sectnum::
+
+.. contents::
+   :local:
+
+Introduction
+============
+
+The purpose of TableGen is to generate complex output files based on
+information from source files that are significantly easier to code than the
+output files would be, and also easier to maintain and modify over time. The
+information is coded in a declarative style involving classes and records,
+which are then processed by TableGen. The internalized records are passed on
+to various backends, which extract information from a subset of the records
+and generate an output file. These output files are typically ``.inc`` files
+for C++, but may be any type of file that the backend developer needs.
+
+This document is a guide to writing a backend for TableGen. It is not a
+complete reference manual, but rather a guide to using the facilities
+provided by TableGen for the backends. For a complete reference to the
+various data structures and functions involved, see the primary TableGen
+header file (``record.h``) and/or the Doxygen documentation.
+
+This document assumes that you have read the :doc:`TableGen Programmer's
+Reference <./ProgRef>`, which provides a detailed reference for coding
+TableGen source files. For a description of the existing backends, see
+:doc:`TableGen BackEnds <./BackEnds>`.
+
+Data Structures
+===============
+
+The following sections describe the data structures that contain the classes
+and records that are collected from the TableGen source files by the
+TableGen parser. Note that the term *class* refers to an abstract record
+class, while the term *record* refers to a concrete record.
+
+Unless otherwise noted, functions associated with classes are instance
+functions.
+
+``RecordKeeper``
+----------------
+
+An instance of the ``RecordKeeper`` class acts as the container for all the
+classes and records parsed and collected by TableGen. The ``RecordKeeper``
+instance is passed to the backend when it is invoked by TableGen. This class
+is usually abbreviated ``RK``.
+
+There are two maps in the recordkeeper, one for classes and one for records
+(the latter often referred to as *defs*). Each map maps the class or record
+name to an instance of the ``Record`` class (see `Record`_), which contains
+all the information about that class or record.
+
+In addition to the two maps, the ``RecordKeeper`` instance contains:
+
+* A map that maps the names of global variables to their values.
+  Global variables are defined in TableGen files with outer
+  ``defvar`` statements.
+
+* A counter for naming anonymous records.
+
+The ``RecordKeeper`` class provides a few useful functions.
+
+* Functions to get the complete class and record maps.
+
+* Functions to get a subset of the records based on their parent classes.
+
+* Functions to get individual classes, records, and globals, by name.
+
+A ``RecordKeeper`` instance can be printed to an output stream with the ``<<``
+operator.
+
+``Record``
+----------
+
+Each class or record built by TableGen is represented by an instance of
+the ``Record`` class. The ``RecordKeeper`` instance contains one map for the
+classes and one for the records. The primary data members of a record are
+the record name, the vector of field names and their values, and the vector of
+superclasses of the record.
+
+The record name is stored as a pointer to an ``Init`` (see `Init`_), which
+is a class whose instances hold TableGen values (sometimes referred to as
+*initializers*). The field names and values are stored in a vector of
+``RecordVal`` instances (see `RecordVal`_), each of which contains both the
+field name and its value. The superclass vector contains a sequence of
+pairs, with each pair including the superclass record and its source
+file location.
+
+In addition to those members, a ``Record`` instance contains:
+
+* A vector of source file locations that includes the record definition
+  itself, plus the locations of any multiclasses involved in its definition.
+
+* For a class record, a vector of the class's template arguments.
+
+* An instance of ``DefInit`` (see `DefInit`_) corresponding to this record.
+
+* A unique record ID.
+
+* A boolean that specifies whether this is a class definition.
+
+* A boolean that specifies whether this is an anonymous record.
+
+The ``Record`` class provides many useful functions.
+
+* Functions to get the record name, fields, source file locations,
+  template arguments, and unique ID.
+
+* Functions to get all the record's superclasses or just its direct
+  superclasses.
+
+* Functions to get a particular field value by specifying its name in various
+  forms, and returning its value in various forms
+  (see `Getting Record Names and Fields`_).
+
+* Boolean functions to check the various attributes of the record.
+
+A ``Record`` instance can be printed to an output stream with the ``<<``
+operator.
+
+
+``RecordVal``
+-------------
+
+Each field of a record is stored in an instance of the ``RecordVal`` class.
+The ``Record`` instance includes a vector of these value instances. A
+``RecordVal`` instance contains the name of the field, stored in an ``Init``
+instance. It also contains the value of the field, likewise stored in an
+``Init``. (A better name for this class might be ``RecordField``.)
+
+In addition to those primary members, the ``RecordVal`` has other data members.
+
+* The source file location of the field definition.
+
+* The type of the field, stored as an instance
+  of the ``RecTy`` class (see `RecTy`_).
+
+The ``RecordVal`` class provides some useful functions.
+
+* Functions to get the name of the field in various forms.
+
+* A function to get the type of the field.
+
+* A function to get the value of the field.
+
+* A function to get the source file location.
+
+Note that field values are more easily obtained directly from the ``Record``
+instance (see `Record`_).
+
+A ``RecordVal`` instance can be printed to an output stream with the ``<<``
+operator.
+
+``RecTy``
+---------
+
+The ``RecTy`` class is used to represent the types of field values. It is
+the base class for a series of subclasses, one for each of the
+available field types. The ``RecTy`` class has one data member that is an
+enumerated type specifying the specific type of field value. (A better
+name for this class might be ``FieldTy``.)
+
+The ``RecTy`` class provides a few useful functions.
+
+* A virtual function to get the type name as a string.
+
+* A virtual function to check whether all the values of this type can
+  be converted to another given type.
+
+* A virtual function to check whether this type is a subtype of
+  another given type.
+
+* A function to get the corresponding ``list``
+  type for lists with elements of this type. For example, the function
+  returns the ``list<int>`` type when called with the ``int`` type.
+
+The subclasses that inherit from ``RecTy`` are
+``BitRecTy``,
+``BitsRecTy``,
+``CodeRecTy``,
+``DagRecTy``,
+``IntRecTy``,
+``ListRecTy``,
+``RecordRecTy``, and
+``StringRecTy``.
+Some of these classes have additional members that
+are described in the following subsections.
+
+*All* of the classes derived from ``RecTy`` provide the ``get()`` function.
+It returns an instance of ``Recty`` corresponding to the derived class. 
+Some of the ``get()`` functions require an argument to
+specify which particular variant of the type is desired. These arguments are
+described in the following subsections.
+
+A ``RecTy`` instance can be printed to an output stream with the ``<<``
+operator.
+
+.. warning::
+  It is not specified whether there is a single ``RecTy`` instance of a
+  particular type or multiple instances.
+
+
+``BitsRecTy``
+~~~~~~~~~~~~~
+
+This class includes a data member with the size of the ``bits`` value and a
+function to get that size.
+
+The ``get()`` function takes the length of the sequence, *n*, and returns the
+``BitsRecTy`` type corresponding to ``bits<``\ *n*\ ``>``.
+
+``ListRecTy``
+~~~~~~~~~~~~~
+
+This class includes a data member that specifies the type of the list's
+elements and a function to get that type.
+
+The ``get()`` function takes the ``RecTy`` *type* of the list members and
+returns the ``ListRecTy`` type corresponding to ``list<``\ *type*\ ``>``.
+
+
+``RecordRecTy``
+~~~~~~~~~~~~~~~
+
+This class includes data members that contain the list of parent classes of
+this record. It also provides a function to obtain the array of classes and
+two functions to get the iterator ``begin()`` and ``end()`` values. The
+class defines a type for the return values of the latter two functions.
+
+.. code-block:: text
+
+  using const_record_iterator = Record * const *;
+
+The ``get()`` function takes an ``ArrayRef`` of pointers to the ``Record``
+instances of the *direct* superclasses of the record and returns the ``RecordRecTy``
+corresponding to the record inheriting from those superclasses.
+
+``Init``
+--------
+
+The ``Init`` class is used to represent TableGen values.  The name derives
+from *initialization value*. This class should not be confused with the
+``RecordVal`` class, which represents record fields, both their names and
+values. The ``Init`` class is the base class for a series of subclasses, one
+for each of the available value types. The primary data member of ``Init``
+is an enumerated type that represents the specific type of the value.
+
+The ``Init`` class provides a few useful functions.
+
+* A function to get the type enumerator.
+
+* A boolean virtual function to determine whether a value is completely
+  specified; that is, has no uninitialized subvalues.
+
+* Virtual functions to get the value as a string.
+
+* Virtual functions to cast the value to other types, implement the bit
+  range feature of TableGen, and implement the list slice feature.
+
+* A virtual function to get a particular bit of the value.
+
+The subclasses that inherit directly from ``Init`` are
+``UnsetInit`` and ``TypedInit``.
+
+An ``Init`` instance can be printed to an output stream with the ``<<``
+operator.
+
+.. warning::
+  It is not specified whether two separate initialization values with
+  the same underlying type and value (e.g., two strings with the value
+  "Hello") are represented by two ``Init``\ s or share the same ``Init``.
+
+``UnsetInit``
+~~~~~~~~~~~~~
+
+This class, a subclass of ``Init``, represents the unset (uninitialized)
+value. The static function ``get()`` can be used to obtain the singleton
+``Init`` of this type.
+
+
+``TypedInit``
+~~~~~~~~~~~~~
+
+This class, a subclass of ``Init``, acts as the parent class of the classes
+that represent specific value types (except for the unset value). These
+classes include ``BitInit``, ``BitsInit``, ``DagInit``, ``DefInit``,
+``IntInit``, ``ListInit``, and ``StringInit``. (There are additional derived
+types used by the TableGen parser.)
+
+This class includes a data member that specifies the ``RecTy`` type of the
+value. It provides a function to get that ``RecTy`` type.
+
+``BitInit``
+~~~~~~~~~~~
+
+The ``BitInit`` class is a subclass of ``TypedInit``. Its instances
+represent the possible values of a bit: 0 or 1. It includes a data member
+that contains the bit.
+
+*All* of the classes derived from ``TypedInit`` provide the following functions.
+
+* A static function named ``get()`` that returns an ``Init`` representing
+  the specified value(s). In the case of ``BitInit``, ``get(true)`` returns
+  an instance of ``BitInit`` representing true, while ``get(false)`` returns
+  an instance
+  representing false. As noted above, it is not specified whether there
+  is exactly one or more than one ``BitInit`` representing true (or false).
+
+* A function named ``GetValue()`` that returns the value of the instance
+  in a more direct form, in this case as a ``bool``.
+
+``BitsInit``
+~~~~~~~~~~~~
+
+The ``BitsInit`` class is a subclass of ``TypedInit``. Its instances
+represent sequences of bits, from high-order to low-order. It includes a
+data member with the length of the sequence and a vector of pointers to
+``Init`` instances, one per bit.
+
+The class provides the usual ``get()`` function. It does not provide the
+``getValue()`` function.
+
+The class provides the following additional functions.
+
+* A function to get the number of bits in the sequence.
+
+* A function that gets a bit specified by an integer index.
+
+``DagInit``
+~~~~~~~~~~~
+
+The ``DagInit`` class is a subclass of ``TypedInit``. Its instances
+represent the possible direct acyclic graphs (``dag``). 
+
+The class includes a pointer to an ``Init`` for the DAG operator and a
+pointer to a ``StringInit`` for the operator name. It includes the count of
+DAG operands and the count of operand names. Finally, it includes a vector of
+pointers to ``Init`` instances for the operands and another to
+``StringInit`` instances for the operand names.
+(The DAG operands are also referred to as *arguments*.)
+
+The class provides two forms of the usual ``get()`` function. It does not
+provide the usual ``getValue()`` function.
+
+The class provides many additional functions:
+
+* Functions to get the operator in various forms and to get the
+  operator name in various forms.
+
+* Functions to determine whether there are any operands and to get the
+  number of operands.
+
+* Functions to the get the operands, both individually and together.
+
+* Functions to determine whether there are any names and to
+  get the number of names
+
+* Functions to the get the names, both individually and together.
+
+* Functions to get the operand iterator ``begin()`` and ``end()`` values.
+
+* Functions to get the name iterator ``begin()`` and ``end()`` values.
+
+The class defines two types for the return values of the operand and name
+iterators.
+
+.. code-block:: text
+
+  using const_arg_iterator = SmallVectorImpl<Init*>::const_iterator;
+  using const_name_iterator = SmallVectorImpl<StringInit*>::const_iterator;
+
+
+``DefInit``
+~~~~~~~~~~~
+
+The ``DefInit`` class is a subclass of ``TypedInit``. Its instances
+represent the records that were collected by TableGen. It includes a data
+member that is a pointer to the record's ``Record`` instance.
+
+The class provides the usual ``get()`` function. It does not provide
+``getValue()``. Instead, it provides ``getDef()``, which returns the
+``Record`` instance.
+
+``IntInit``
+~~~~~~~~~~~
+
+The ``IntInit`` class is a subclass of ``TypedInit``. Its instances
+represent the possible values of a 64-bit integer. It includes a data member
+that contains the integer.
+
+The class provides the usual ``get()`` and ``getValue()`` functions. The
+latter function returns the integer as an ``int64_t``.
+
+The class also provides a function, ``getBit()``, to obtain a specified bit
+of the integer value.
+
+``ListInit``
+~~~~~~~~~~~~
+
+The ``ListInit`` class is a subclass of ``TypedInit``. Its instances
+represent lists of elements of some type. It includes a data member with the
+length of the list and a vector of pointers to ``Init`` instances, one per
+element.
+
+The class provides the usual ``get()`` and ``getValues()`` functions. The
+latter function returns an ``ArrayRef`` of the vector of pointers to ``Init``
+instances.
+
+The class provides these additional functions.
+
+* A function to get the element type.
+
+* Functions to get the length of the vector and to determine whether
+  it is empty.
+
+* Functions to get an element specified by an integer index and return
+  it in various forms.
+
+* Functions to get the iterator ``begin()`` and ``end()`` values. The
+  class defines a type for the return type of these two functions.
+
+.. code-block:: text
+
+  using const_iterator = Init *const *;
+ 
+
+``StringInit``
+~~~~~~~~~~~~~~
+
+The ``StringInit`` class is a subclass of ``TypedInit``. Its instances
+represent arbitrary-length strings. It includes a data member
+that contains a ``StringRef`` of the value.
+
+The class provides the usual ``get()`` and ``getValue()`` functions. The
+latter function returns the ``StringRef``.
+
+Creating a New Backend
+======================
+
+The following steps are required to create a new backend for TableGen.
+
+#. Invent a name for your backend C++ file, say ``GenAddressModes``.
+
+#. Write the new backend, using the file ``TableGenBackendSkeleton.cpp``
+   as a starting point.
+
+#. Determine which instance of TableGen requires the new backend. There is
+   one instance for Clang and another for LLVM. Or you may be building
+   your own instance.
+
+#. Modify the selected ``tablegen.cpp`` to include your new backend.
+
+  a. Add the name to the enumerated type ``ActionType``.
+
+  #. Add a keyword to the ``ActionType`` command option using the
+     ``clEnumValN()`` function.
+
+  #. Add a case to the ``switch`` statement in the *xxx*\ ``TableGenMain()``
+     function. It should invoke the "main function" of your backend, which
+     in this case, according to convention, is named ``EmitAddressModes``.
+
+5. Add a declaration of your "main function" to the corresponding 
+   ``TableGenBackends.h`` header file.
+
+#. Add your backend C++ file to the appropriate ``CMakeLists.txt`` file so
+   that it will be built.
+
+#. Add your C++ file to the system.
+
+The Backend Skeleton
+====================
+
+The file ``TableGenBackendSkeleton.cpp`` provides a skeleton C++ translation
+unit for writing a new TableGen backend. Here are a few notes on the file.
+
+* The list of includes is the minimal list required by most backends.
+
+* As with all LLVM C++ files, it has a ``using namespace llvm;`` statement.
+  It also has an anonymous namespace that contains all the file-specific
+  data structure definitions, along with the class embodying the emitter
+  data members and functions. Continuing with the ``GenAddressModes`` example,
+  this class is named ``AddressModesEmitter``.
+
+* The constructor for the emitter class accepts a ``RecordKeeper`` reference,
+  typically named ``RK``. The ``RecordKeeper`` reference is saved in a data
+  member so that records can be obtained from it. This data member is usually
+  named ``Records``.
+
+* One function is named ``run``. It is invoked by the backend's "main
+  function" to collect records and emit the output file. It accepts an instance
+  of the ``raw_ostream`` class, typically named ``OS``. The output file is
+  emitted by writing to this stream.
+
+* The ``run`` function should use the ``emitSourceFileHeader`` helper function
+  to include a standard header in the emitted file.
+
+* The only function in the ``llvm`` namespace is the backend "main function."
+  In this example, it is named ``EmitAddressModes``. It creates an instance
+  of the ``AddressModesEmitter`` class, passing the ``RecordKeeper``
+  instance, then invokes the ``run`` function, passing the ``raw_ostream``
+  instance.
+
+All the examples in the remainder of this document will assume the naming
+conventions used in the skeleton file.
+
+Getting Classes
+===============
+
+The ``RecordKeeper`` class provides two functions for getting the
+``Record`` instances for classes defined in the TableGen files.
+
+* ``getClasses()`` returns a ``RecordMap`` reference for all the classes.
+
+* ``getClass(``\ *name*\ ``)`` returns a ``Record`` reference for the named
+  class.
+
+If you need to iterate over all the class records:
+
+.. code-block:: text
+
+  for (auto ClassPair : Records.getClasses()) {
+    Record *ClassRec = ClassPair.second.get();
+    ...
+  }
+
+``ClassPair.second`` gets the class's ``unique_ptr``, then ``.get()`` gets the
+class ``Record`` itself.
+
+
+Getting Records
+===============
+
+The ``RecordKeeper`` class provides four functions for getting the
+``Record`` instances for concrete records defined in the TableGen files.
+
+* ``getDefs()`` returns a ``RecordMap`` reference for all the concrete
+  records.
+
+* ``getDef(``\ *name*\ ``)`` returns a ``Record`` reference for the named
+  concrete record.
+
+* ``getAllDerivedDefinitions(``\ *classname*\ ``)`` returns a vector of
+  ``Record`` references for the concrete records that derive from the
+  given class.
+
+* ``getAllDerivedDefinitions(``\ *classnames*\ ``)`` returns
+  a vector of ``Record`` references for the concrete records that derive from
+  *all* of the given classes.
+
+This statement obtains all the records that derive from the ``Attribute``
+class and iterates over them.
+
+.. code-block:: text
+
+  auto AttrRecords = Records.getAllDerivedDefinitions("Attribute");
+  for (Record *AttrRec : AttrRecords) {
+    ...
+  }
+
+Getting Record Names and Fields
+===============================
+
+As described above (see `Record`_), there are multiple functions that
+return the name of a record. One particularly useful one is
+``getNameInitAsString()``, which returns the name as a ``std::string``.
+
+There are also multiple functions that return the fields of a record. To
+obtain and iterate over all the fields:
+
+.. code-block:: text
+
+  for (const RecordVal &Field : SomeRec->getValues()) {
+    ...
+  }
+
+You will recall that ``RecordVal`` is the class whose instances contain
+information about the fields in records.
+
+The ``getValue()`` function returns the ``RecordVal`` instance for a field
+specified by name. There are multiple overloaded functions, some taking a
+``StringRef`` and others taking a ``const Init *``. Some functions return a
+``RecordVal *`` and others return a ``const RecordVal *``. If the field does
+not exist, a fatal error message is printed.
+
+More often than not, you are interested in the value of the field, not all
+the information in the ``RecordVal``. There is a large set of functions that
+take a field name in some form and return its value. One function,
+``getValueInit``, returns the value as an ``Init *``. Another function,
+``isValueUnset``, returns a boolean specifying whether the value is unset
+(uninitialized).
+
+Most of the functions return the value in some more useful form. For
+example:
+
+.. code-block:: text
+
+  std::vector<int64_t> RegCosts =
+      SomeRec->getValueAsListOfInts("RegCosts");
+
+The field ``RegCosts`` is assumed to be a list of integers. That list is
+returned as a ``std::vector`` of 64-bit integers. If the field is not a list
+of integers, a fatal error message is printed.
+
+Here is a function that returns a field value as a ``Record``, but returns
+null if the field does not exist.
+
+.. code-block:: text
+
+  if (Record *BaseRec = SomeRec->getValueAsOptionalDef(BaseFieldName)) {
+    ...
+  }
+
+The field is assumed to have another record as its value. That record is returned
+as a pointer to a ``Record``. If the field does not exist or is unset, the
+functions returns null.  
+
+Getting Record Superclasses
+===========================
+
+The ``Record`` class provides a function to obtain the superclasses of a
+record. It is named ``getSuperClasses`` and returns an ``ArrayRef`` of an
+array of ``std::pair`` pairs. The superclasses are in post-order: the order
+in which the superclasses were visited while copying their fields into the
+record. Each pair consists of a pointer to the ``Record`` instance for a
+superclass record and an instance of the ``SMRange`` class. The range
+indicates the source file locations of the beginning and end of the class
+definition.
+
+This example obtains the superclasses of the ``Prototype`` record and then
+iterates over the pairs in the returned array.
+
+.. code-block:: text
+
+  ArrayRef<std::pair<Record *, SMRange>>
+      Superclasses = Prototype->getSuperClasses();
+  for (const auto &SuperPair : Superclasses) {
+    ...
+  }
+
+The ``Record`` class also provides a function, ``getDirectSuperClasses``, to
+append the *direct* superclasses of a record to a given vector of type
+``SmallVectorImpl<Record *>``.
+
+Emitting Text to the Output Stream
+==================================
+
+The ``run`` function is passed a ``raw_ostream`` to which it prints the
+output file. By convention, this stream is saved in the emitter class member
+named ``OS``, although some ``run`` functions are simple and just use the
+stream without saving it. The output can be produced by writing values
+directly to the output stream, or by using the ``std::format()`` or
+``llvm::formatv()`` functions.
+
+.. code-block:: text
+
+  OS << "#ifndef " << NodeName << "\n";
+
+  OS << format("0x%0*x, ", Digits, Value);
+
+Instances of the following classes can be printed using the ``<<`` operator:
+``RecordKeeper``,
+``Record``,
+``RecTy``,
+``RecordVal``, and
+``Init``.
+
+The helper function ``emitSourceFileHeader()`` prints the header comment
+that should be included at the top of every output file. A call to it is
+included in the skeleton backend file ``TableGenBackendSkeleton.cpp``.
+
+Printing Error Messages
+=======================
+
+TableGen records are often derived from multiple classes and also often
+defined through a sequence of multiclasses. Because of this, it can be
+difficult for backends to report clear error messages with accurate source
+file locations.  To make error reporting easier, five error reporting
+functions are provided, each with four overloads.
+
+* ``PrintWarning`` prints a message tagged as a warning.
+
+* ``PrintError`` prints a message tagged as an error.
+
+* ``PrintFatalError`` prints a message tagged as an error and then terminates.
+
+* ``PrintNote`` prints a note. It is often used after one of the previous
+  functions to provide more information.
+
+* ``PrintFatalNote`` prints a note and then terminates.
+
+Each of these five functions is overloaded four times. 
+
+* ``PrintError(const Twine &Msg)``:
+  Prints the message with no source file location.
+
+* ``PrintError(ArrayRef<SMLoc> ErrorLoc, const Twine &Msg)``: 
+  Prints the message followed by the specified source line,
+  along with a pointer to the item in error. The array of
+  source file locations is typically taken from a ``Record`` instance.
+
+* ``PrintError(const Record *Rec, const Twine &Msg)``:
+  Prints the message followed by the source line associated with the
+  specified record (see `Record`_).
+
+* ``PrintError(const RecordVal *RecVal, const Twine &Msg)``:
+  Prints the message followed by the source line associated with the
+  specified record field (see `RecordVal`_).
+
+Using these functions, the goal is to produce the most specific error report
+possible.
+
+Debugging Tools
+===============
+
+TableGen provides some tools to aid in debugging backends.
+
+The ``PrintRecords`` Backend
+----------------------------
+
+The TableGen command option ``--print-records`` invokes a simple backend
+that prints all the classes and records defined in the source files. This is
+the default backend option. The format of the output is guaranteed to be
+constant over time, so that the output can be compared in tests. The output
+looks like this:
+
+.. code-block:: text
+
+  ------------- Classes -----------------
+  ...
+  class XEntry<string XEntry:str = ?, int XEntry:val1 = ?> { // XBase
+    string Str = XEntry:str;
+    bits<8> Val1 = { !cast<bits<8>>(XEntry:val1){7}, ... };
+    bit Val3 = 1;
+  }
+  ...
+  ------------- Defs -----------------
+  def ATable {	// GenericTable
+    string FilterClass = "AEntry";
+    string CppTypeName = "AEntry";
+    list<string> Fields = ["Str", "Val1", "Val2"];
+    list<string> PrimaryKey = ["Val1", "Val2"];
+    string PrimaryKeyName = "lookupATableByValues";
+    bit PrimaryKeyEarlyOut = 0;
+  }
+  ...
+  def anonymous_0 {	// AEntry
+    string Str = "Bob";
+    bits<8> Val1 = { 0, 0, 0, 0, 0, 1, 0, 1 };
+    bits<10> Val2 = { 0, 0, 0, 0, 0, 0, 0, 0, 1, 1 };
+  }
+
+Classes are shown with their template arguments, parent classes (following
+``//``), and fields. Records are shown with their parent classes and
+fields. Note that anonymous records are named ``anonymous_0``,
+``anonymous_1``, etc.
+
+The ``PrintDetailedRecords`` Backend
+------------------------------------
+
+The TableGen command option ``--print-detailed-records`` invokes a backend
+that prints all the global variables, classes, and records defined in the
+source files. The format of the output is *not* guaranteed to be constant
+over time. The output looks like this.
+
+.. code-block:: text
+
+  DETAILED RECORDS for file llvm-project\llvm\lib\target\arc\arc.td
+  
+  -------------------- Global Variables (5) --------------------
+  
+  AMDGPUBufferIntrinsics = [int_amdgcn_buffer_load_format, ...
+  AMDGPUImageDimAtomicIntrinsics = [int_amdgcn_image_atomic_swap_1d, ...
+  ...
+  -------------------- Classes (758) --------------------
+  
+  AMDGPUBufferLoad  |IntrinsicsAMDGPU.td:879|
+    Template args:
+      LLVMType AMDGPUBufferLoad:data_ty = llvm_any_ty  |IntrinsicsAMDGPU.td:879|
+    Superclasses: (SDPatternOperator) Intrinsic AMDGPURsrcIntrinsic
+    Fields:
+      list<SDNodeProperty> Properties = [SDNPMemOperand]  |Intrinsics.td:348|
+      string LLVMName = ""  |Intrinsics.td:343|
+  ...
+  -------------------- Records (12303) --------------------
+  
+  AMDGPUSample_lz_o  |IntrinsicsAMDGPU.td:560|
+    Defm sequence: |IntrinsicsAMDGPU.td:584| |IntrinsicsAMDGPU.td:566|
+    Superclasses: AMDGPUSampleVariant
+    Fields:
+      string UpperCaseMod = "_LZ_O"  |IntrinsicsAMDGPU.td:542|
+      string LowerCaseMod = "_lz_o"  |IntrinsicsAMDGPU.td:543|
+  ...
+
+* Global variables defined with outer ``defvar`` statements are shown with
+  their values.
+
+* The classes are shown with their source location, template arguments,
+  superclasses, and fields. 
+
+* The records are shown with their source location, ``defm`` sequence,
+  superclasses, and fields.
+
+Superclasses are shown in the order processed, with indirect superclasses in
+parentheses. Each field is shown with its value and the source location at
+which it was set.
+The ``defm`` sequence gives the locations of the ``defm`` statements that
+were involved in generating the record, in the order they were invoked.
+
+Timing TableGen Phases
+----------------------
+
+TableGen provides a phase timing feature that produces a report of the time
+used by the various phases of parsing the source files and running the
+selected backend. This feature is enabled with the ``--time-phases`` option
+of the TableGen command.
+
+If the backend is *not* instrumented for timing, then a report such as the
+following is produced. This is the timing for the
+``--print-detailed-records`` backend run on the AMDGPU target.
+
+.. code-block:: text
+
+  ===-------------------------------------------------------------------------===
+                               TableGen Phase Timing
+  ===-------------------------------------------------------------------------===
+    Total Execution Time: 101.0106 seconds (102.4819 wall clock)
+  
+     ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
+    85.5197 ( 84.9%)   0.1560 ( 50.0%)  85.6757 ( 84.8%)  85.7009 ( 83.6%)  Backend overall
+    15.1789 ( 15.1%)   0.0000 (  0.0%)  15.1789 ( 15.0%)  15.1829 ( 14.8%)  Parse, build records
+     0.0000 (  0.0%)   0.1560 ( 50.0%)   0.1560 (  0.2%)   1.5981 (  1.6%)  Write output
+    100.6986 (100.0%)   0.3120 (100.0%)  101.0106 (100.0%)  102.4819 (100.0%)  Total
+
+Note that all the time for the backend is lumped under "Backend overall".
+
+If the backend is instrumented for timing, then its processing is
+divided into phases and each one timed separately. This is the timing for
+the ``--emit-dag-isel`` backend run on the AMDGPU target.
+
+.. code-block:: text
+
+  ===-------------------------------------------------------------------------===
+                               TableGen Phase Timing
+  ===-------------------------------------------------------------------------===
+    Total Execution Time: 746.3868 seconds (747.1447 wall clock)
+  
+     ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
+    657.7938 ( 88.1%)   0.1404 ( 90.0%)  657.9342 ( 88.1%)  658.6497 ( 88.2%)  Emit matcher table
+    70.2317 (  9.4%)   0.0000 (  0.0%)  70.2317 (  9.4%)  70.2700 (  9.4%)  Convert to matchers
+    14.8825 (  2.0%)   0.0156 ( 10.0%)  14.8981 (  2.0%)  14.9009 (  2.0%)  Parse, build records
+     2.1840 (  0.3%)   0.0000 (  0.0%)   2.1840 (  0.3%)   2.1791 (  0.3%)  Sort patterns
+     1.1388 (  0.2%)   0.0000 (  0.0%)   1.1388 (  0.2%)   1.1401 (  0.2%)  Optimize matchers
+     0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0050 (  0.0%)  Write output
+    746.2308 (100.0%)   0.1560 (100.0%)  746.3868 (100.0%)  747.1447 (100.0%)  Total
+
+The backend has been divided into four phases and timed separately.
+
+If you want to instrument a backend, refer to the backend ``DAGISelEmitter.cpp``
+and search for ``Records.startTimer``.
\ No newline at end of file