mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2025-10-30 16:17:05 +00:00
aa55c8cc38
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11356 91177308-0d34-0410-b5e6-96231b3b80d8
654 lines
22 KiB
HTML
654 lines
22 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
|
|
"http://www.w3.org/TR/html4/strict.dtd">
|
|
<html>
|
|
<head>
|
|
<title>TableGen Fundamentals</title>
|
|
<link rel="stylesheet" href="llvm.css" type="text/css">
|
|
</head>
|
|
<body>
|
|
|
|
<div class="doc_title">TableGen Fundamentals</div>
|
|
|
|
<ul>
|
|
<li><a href="#introduction">Introduction</a></li>
|
|
<ol>
|
|
<li><a href="#concepts">Basic concepts</a></li>
|
|
<li><a href="#example">An example record</a></li>
|
|
<li><a href="#running">Running TableGen</a></li>
|
|
</ol>
|
|
<li><a href="#syntax">TableGen syntax</a></li>
|
|
<ol>
|
|
<li><a href="#primitives">TableGen primitives</a></li>
|
|
<ol>
|
|
<li><a href="#comments">TableGen comments</a></li>
|
|
<li><a href="#types">The TableGen type system</a></li>
|
|
<li><a href="#values">TableGen values and expressions</a></li>
|
|
</ol>
|
|
<li><a href="#classesdefs">Classes and definitions</a></li>
|
|
<ol>
|
|
<li><a href="#valuedef">Value definitions</a></li>
|
|
<li><a href="#recordlet">'let' expressions</a></li>
|
|
<li><a href="#templateargs">Class template arguments</a></li>
|
|
</ol>
|
|
<li><a href="#filescope">File scope entities</a></li>
|
|
<ol>
|
|
<li><a href="#include">File inclusion</a></li>
|
|
<li><a href="#globallet">'let' expressions</a></li>
|
|
</ol>
|
|
</ol>
|
|
<li><a href="#backends">TableGen backends</a></li>
|
|
<ol>
|
|
<li><a href="#">todo</a></li>
|
|
</ol>
|
|
<li><a href="#codegenerator">The LLVM code generator</a></li>
|
|
<ol>
|
|
<li><a href="#">todo</a></li>
|
|
</ol>
|
|
</ul>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"><a name="introduction">Introduction</a></div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>TableGen's purpose is to help a human develop and maintain records of
|
|
domain-specific information. Because there may be a large number of these
|
|
records, it is specifically designed to allow writing flexible descriptions and
|
|
for common features of these records to be factored out. This reduces the
|
|
amount of duplication in the description, reduces the chance of error, and
|
|
makes it easier to structure domain specific information.</p>
|
|
|
|
<p>The core part of TableGen <a href="#syntax">parses a file</a>, instantiates
|
|
the declarations, and hands the result off to a domain-specific "<a
|
|
href="#backends">TableGen backend</a>" for processing. The current major user
|
|
of TableGen is the <a href="#codegenerator">LLVM code generator</a>.
|
|
</p>
|
|
|
|
<p>
|
|
Note that if you work on TableGen much, and use emacs or vim, that you can find
|
|
an emacs "TableGen mode" and a vim language file in <tt>llvm/utils/emacs</tt>
|
|
and <tt>llvm/utils/vim</tt> directory of your LLVM distribution, respectively.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="running">Basic concepts</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>
|
|
TableGen files consist of two key parts: 'classes' and 'definitions', both of
|
|
which are considered 'records'.
|
|
</p>
|
|
|
|
<p>
|
|
<b>TableGen records</b> have a unique name, a list of values, and a list of
|
|
superclasses. The list of values is main data that TableGen builds for each
|
|
record, it is this that holds the domain specific information for the
|
|
application. The interpretation of this data is left to a specific <a
|
|
href="#backends">TableGen backend</a>, but the structure and format rules are
|
|
taken care of and fixed by TableGen.
|
|
</p>
|
|
|
|
<p>
|
|
<b>TableGen definitions</b> are the concrete form of 'records'. These generally
|
|
do not have any undefined values, and are marked with the '<tt>def</tt>'
|
|
keyword.
|
|
</p>
|
|
|
|
<p>
|
|
<b>TableGen classes</b> are abstract records that are used to build and describe
|
|
other records. These 'classes' allow the end-user to build abstractions for
|
|
either the domain they are targetting (such as "Register", "RegisterClass", and
|
|
"Instruction" in the LLVM code generator) or for the implementor to help factor
|
|
out common properties of records (such as "FPInst", which is used to represent
|
|
floating point instructions in the X86 backend). TableGen keeps track of all of
|
|
the classes that are used to build up a definition, so the backend can find all
|
|
definitions of a particular class, such as "Instruction".
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="example">An example record</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>
|
|
With no other arguments, TableGen parses the specified file and prints out all
|
|
of the classes, then all of the definitions. This is a good way to see what the
|
|
various definitions expand to fully. Running this on the <tt>X86.td</tt> file
|
|
prints this (at the time of this writing):
|
|
</p>
|
|
|
|
<p>
|
|
<pre>
|
|
...
|
|
<b>def</b> ADDrr8 { <i>// Instruction X86Inst I2A8 Pattern</i>
|
|
<b>string</b> Name = "add";
|
|
<b>string</b> Namespace = "X86";
|
|
<b>list</b><Register> Uses = [];
|
|
<b>list</b><Register> Defs = [];
|
|
<b>bit</b> isReturn = 0;
|
|
<b>bit</b> isBranch = 0;
|
|
<b>bit</b> isCall = 0;
|
|
<b>bit</b> isTwoAddress = 1;
|
|
<b>bit</b> isTerminator = 0;
|
|
<b>dag</b> Pattern = (set R8, (plus R8, R8));
|
|
<b>bits</b><8> Opcode = { 0, 0, 0, 0, 0, 0, 0, 0 };
|
|
Format Form = MRMDestReg;
|
|
<b>bits</b><5> FormBits = { 0, 0, 0, 1, 1 };
|
|
ArgType Type = Arg8;
|
|
<b>bits</b><3> TypeBits = { 0, 0, 1 };
|
|
<b>bit</b> hasOpSizePrefix = 0;
|
|
<b>bit</b> printImplicitUses = 0;
|
|
<b>bits</b><4> Prefix = { 0, 0, 0, 0 };
|
|
FPFormat FPForm = ?;
|
|
<b>bits</b><3> FPFormBits = { 0, 0, 0 };
|
|
}
|
|
...
|
|
</pre><p>
|
|
|
|
<p>
|
|
This definition corresponds to an 8-bit register-register add instruction in the
|
|
X86. The string after the '<tt>def</tt>' string indicates the name of the
|
|
record ("<tt>ADDrr8</tt>" in this case), and the comment at the end of the line
|
|
indicates the superclasses of the definition. The body of the record contains
|
|
all of the data that TableGen assembled for the record, indicating that the
|
|
instruction is part of the "X86" namespace, should be printed as "<tt>add</tt>"
|
|
in the assembly file, it is a two-address instruction, has a particular
|
|
encoding, etc. The contents and semantics of the information in the record is
|
|
specific to the needs of the X86 backend, and is only shown as an example.
|
|
</p>
|
|
|
|
<p>
|
|
As you can see, a lot of information is needed for every instruction supported
|
|
by the code generator, and specifying it all manually would be unmaintainble,
|
|
prone to bugs, and tiring to do in the first place. Because we are using
|
|
TableGen, all of the information was derived from the following definition:
|
|
</p>
|
|
|
|
<p><pre>
|
|
<b>def</b> ADDrr8 : I2A8<"add", 0x00, MRMDestReg>,
|
|
Pattern<(set R8, (plus R8, R8))>;
|
|
</pre></p>
|
|
|
|
<p>
|
|
This definition makes use of the custom I2A8 (two address instruction with 8-bit
|
|
operand) class, which is defined in the X86-specific TableGen file to factor out
|
|
the common features that instructions of its class share. A key feature of
|
|
TableGen is that it allows the end-user to define the abstractions they prefer
|
|
to use when describing their information.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="running">Running TableGen</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>
|
|
TableGen runs just like any other LLVM tool. The first (optional) argument
|
|
specifies the file to read. If a filename is not specified, <tt>tblgen</tt>
|
|
reads from standard input.
|
|
</p>
|
|
|
|
<p>
|
|
To be useful, one of the <a href="#backends">TableGen backends</a> must be used.
|
|
These backends are selectable on the command line (type '<tt>tblgen --help</tt>'
|
|
for a list). For example, to get a list of all of the definitions that subclass
|
|
a particular type (which can be useful for building up an enum list of these
|
|
records), use the <tt>--print-enums</tt> option:
|
|
</p>
|
|
|
|
<p><pre>
|
|
$ tblgen X86.td -print-enums -class=Register
|
|
AH, AL, AX, BH, BL, BP, BX, CH, CL, CX, DH, DI, DL, DX,
|
|
EAX, EBP, EBX, ECX, EDI, EDX, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6,
|
|
SI, SP, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
|
|
|
|
$ tblgen X86.td -print-enums -class=Instruction
|
|
ADCrr32, ADDri16, ADDri16b, ADDri32, ADDri32b, ADDri8, ADDrr16, ADDrr32,
|
|
ADDrr8, ADJCALLSTACKDOWN, ADJCALLSTACKUP, ANDri16, ANDri16b, ANDri32, ANDri32b,
|
|
ANDri8, ANDrr16, ANDrr32, ANDrr8, BSWAPr32, CALLm32, CALLpcrel32, ...
|
|
</pre></p>
|
|
|
|
<p>
|
|
The default backend prints out all of the records, as described <a
|
|
href="#example">above</a>.
|
|
</p>
|
|
|
|
<p>
|
|
If you plan to use TableGen for some purpose, you will most likely have to <a
|
|
href="#backends">write a backend</a> that extracts the information specific to
|
|
what you need and formats it in the appropriate way.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"><a name="syntax">TableGen syntax</a></div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>
|
|
TableGen doesn't care about the meaning of data (that is up to the backend to
|
|
define), but it does care about syntax, and it enforces a simple type system.
|
|
This section describes the syntax and the constructs allowed in a TableGen file.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="primitives">TableGen primitives</tt></a>
|
|
</div>
|
|
|
|
<!----------------------------------------------------------------------------->
|
|
<div class="doc_subsubsection">
|
|
<a name="comments">TableGen comments</tt></a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>TableGen supports BCPL style "<tt>//</tt>" comments, which run to the end of
|
|
the line, and it also supports <b>nestable</b> "<tt>/* */</tt>" comments.</p>
|
|
|
|
</div>
|
|
|
|
|
|
<!----------------------------------------------------------------------------->
|
|
<div class="doc_subsubsection">
|
|
<a name="types">The TableGen type system</tt></a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
<p>
|
|
TableGen files are strongly typed, in a simple (but complete) type-system.
|
|
These types are used to perform automatic conversions, check for errors, and to
|
|
help interface designers constrain the input that they allow. Every <a
|
|
href="#valuedef">value definition</a> is required to have an associated type.
|
|
</p>
|
|
|
|
<p>
|
|
TableGen supports a mixture of very low-level types (such as <tt>bit</tt>) and
|
|
very high-level types (such as <tt>dag</tt>). This flexibility is what allows
|
|
it to describe a wide range of information conveniently and compactly. The
|
|
TableGen types are:
|
|
</p>
|
|
|
|
<p>
|
|
<ul>
|
|
<li>"<tt><b>bit</b></tt>" - A 'bit' is a boolean value that can hold either 0 or
|
|
1.</li>
|
|
|
|
<li>"<tt><b>int</b></tt>" - The 'int' type represents a simple 32-bit integer
|
|
value, such as 5.</li>
|
|
|
|
<li>"<tt><b>string</b></tt>" - The 'string' type represents an ordered sequence
|
|
of characters of arbitrary length.</li>
|
|
|
|
<li>"<tt><b>bits</b><n></tt>" - A 'bits' type is an arbitrary, but fixed,
|
|
size integer that is broken up into individual bits. This type is useful
|
|
because it can handle some bits being defined while others are undefined.</li>
|
|
|
|
<li>"<tt><b>list</b><ty></tt>" - This type represents a list whose
|
|
elements are some other type. The contained type is arbitrary: it can even be
|
|
another list type.</li>
|
|
|
|
<li>Class type - Specifying a class name in a type context means that the
|
|
defined value must be a subclass of the specified class. This is useful in
|
|
conjunction with the "list" type, for example, to constrain the elements of the
|
|
list to a common base class (e.g., a <tt><b>list</b><Register></tt> can
|
|
only contain definitions derived from the "<tt>Register</tt>" class).</li>
|
|
|
|
<li>"<tt><b>code</b></tt>" - This represents a big hunk of text. NOTE: I don't
|
|
remember why this is distinct from string!</li>
|
|
|
|
<li>"<tt><b>dag</b></tt>" - This type represents a nestable directed graph of
|
|
elements.</li>
|
|
</ul>
|
|
</p>
|
|
|
|
<p>
|
|
To date, these types have been sufficient for describing things that TableGen
|
|
has been used for, but it is straight-forward to extend this list if needed.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!----------------------------------------------------------------------------->
|
|
<div class="doc_subsubsection">
|
|
<a name="values">TableGen values and expressions</tt></a>
|
|
</div>
|
|
|
|
<div>
|
|
<p>
|
|
TableGen allows for a pretty reasonable number of different expression forms
|
|
when building up values. These forms allow the TableGen file to be written in a
|
|
natural syntax and flavor for the application. The current expression forms
|
|
supported include:
|
|
</p>
|
|
|
|
<p><ul>
|
|
<li>? - Uninitialized field.</li>
|
|
<li>0b1001011 - Binary integer value.</li>
|
|
<li>07654321 - Octal integer value (indicated by a leading 0).</li>
|
|
<li>7 - Decimal integer value.</li>
|
|
<li>0x7F - Hexadecimal integer value.</li>
|
|
<li>"foo" - String value.</li>
|
|
<li>[{ .... }] - Code fragment.</li>
|
|
<li>[ X, Y, Z ] - List value.</li>
|
|
<li>{ a, b, c } - Initializer for a "bits<3>" value.</li>
|
|
<li>value - Value reference.</li>
|
|
<li>value{17} - Access to one or more bits of a value.</li>
|
|
<li>DEF - Reference to a record definition.</li>
|
|
<li>X.Y - Reference to the subfield of a value.</li>
|
|
|
|
<li>(DEF a, b) - A dag value. The first element is required to be a record
|
|
definition, the remaining elements in the list may be arbitrary other values,
|
|
including nested 'dag' values.</li>
|
|
|
|
</ul></p>
|
|
|
|
<p>
|
|
Note that all of the values have rules specifying how they convert to values
|
|
for different types. These rules allow you to assign a value like "7" to a
|
|
"bits<4>" value, for example.
|
|
</p>
|
|
|
|
|
|
|
|
</div>
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="classesdefs">Classes and definitions</tt></a>
|
|
</div>
|
|
|
|
<div>
|
|
<p>
|
|
As mentioned in the <a href="#concepts">intro</a>, classes and definitions
|
|
(collectively known as 'records') in TableGen are the main high-level unit of
|
|
information that TableGen collects. Records are defined with a <tt>def</tt> or
|
|
<tt>class</tt> keyword, the record name, and an optional list of "<a
|
|
href="templateargs">template arguments</a>". If the record has superclasses,
|
|
they are specified as a comma seperated list that starts with a colon character
|
|
(":"). If <a href="#valuedef">value definitions</a> or <a href="#recordlet">let
|
|
expressions</a> are needed for the class, they are enclosed in curly braces
|
|
("{}"); otherwise, the record ends with a semicolon. Here is a simple TableGen
|
|
file:
|
|
</p>
|
|
|
|
<p><pre>
|
|
<b>class</b> C { <b>bit</b> V = 1; }
|
|
<b>def</b> X : C;
|
|
<b>def</b> Y : C {
|
|
<b>string</b> Greeting = "hello";
|
|
}
|
|
</pre></p>
|
|
|
|
<p>
|
|
This example defines two definitions, <tt>X</tt> and <tt>Y</tt>, both of which
|
|
derive from the <tt>C</tt> class. Because of this, they both get the <tt>V</tt>
|
|
bit value. The <tt>Y</tt> definition also gets the Greeting member as well.
|
|
</p>
|
|
|
|
<p>
|
|
In general, classes are useful for collecting together the commonality between a
|
|
group of records and isolating it in a single place. Also, classes permit the
|
|
specification of default values for their subclasses, allowing the subclasses to
|
|
override them as they wish.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!----------------------------------------------------------------------------->
|
|
<div class="doc_subsubsection">
|
|
<a name="valuedef">Value definitions</tt></a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
<p>
|
|
Value definitions define named entries in records. A value must be defined
|
|
before it can be referred to as the operand for another value definition or
|
|
before the value is reset with a <a href="#recordlet">let expression</a>. A
|
|
value is defined by specifying a <a href="#types">TableGen type</a> and a name.
|
|
If an initial value is available, it may be specified after the type with an
|
|
equal sign. Value definitions require terminating semicolons.
|
|
</div>
|
|
|
|
<!----------------------------------------------------------------------------->
|
|
<div class="doc_subsubsection">
|
|
<a name="recordlet">'let' expressions</tt></a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
<p>
|
|
A record-level let expression is used to change the value of a value definition
|
|
in a record. This is primarily useful when a superclass defines a value that a
|
|
derived class or definition wants to override. Let expressions consist of the
|
|
'<tt>let</tt>' keyword followed by a value name, an equal sign ("="), and a new
|
|
value. For example, a new class could be added to the example above, redefining
|
|
the <tt>V</tt> field for all of its subclasses:</p>
|
|
|
|
<p><pre>
|
|
<b>class</b> D : C { let V = 0; }
|
|
<b>def</b> Z : D;
|
|
</pre></p>
|
|
|
|
<p>
|
|
In this case, the <tt>Z</tt> definition will have a zero value for its "V"
|
|
value, despite the fact that it derives (indirectly) from the <tt>C</tt> class,
|
|
because the <tt>D</tt> class overrode its value.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!----------------------------------------------------------------------------->
|
|
<div class="doc_subsubsection">
|
|
<a name="templateargs">Class template arguments</tt></a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
<p>
|
|
TableGen permits the definition of parameterized classes as well as normal
|
|
concrete classes. Parameterized TableGen classes specify a list of variable
|
|
bindings (which may optionally have defaults) that are bound when used. Here is
|
|
a simple example:</p>
|
|
|
|
<p><pre>
|
|
<b>class</b> FPFormat<<b>bits</b><3> val> {
|
|
<b>bits</b><3> Value = val;
|
|
}
|
|
<b>def</b> NotFP : FPFormat<0>;
|
|
<b>def</b> ZeroArgFP : FPFormat<1>;
|
|
<b>def</b> OneArgFP : FPFormat<2>;
|
|
<b>def</b> OneArgFPRW : FPFormat<3>;
|
|
<b>def</b> TwoArgFP : FPFormat<4>;
|
|
<b>def</b> SpecialFP : FPFormat<5>;
|
|
</pre></p>
|
|
|
|
<p>
|
|
In this case, template arguments are used as a space efficient way to specify a
|
|
list of "enumeration values", each with a "Value" field set to the specified
|
|
integer.</p>
|
|
|
|
<p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
|
|
useful in conjunction with template arguments. As an example:</p>
|
|
|
|
<p><pre>
|
|
<b>class</b> ModRefVal<<b>bits</b><2> val> {
|
|
<b>bits</b><2> Value = val;
|
|
}
|
|
|
|
<b>def</b> None : ModRefVal<0>;
|
|
<b>def</b> Mod : ModRefVal<1>;
|
|
<b>def</b> Ref : ModRefVal<2>;
|
|
<b>def</b> ModRef : ModRefVal<3>;
|
|
|
|
<b>class</b> Value<ModRefVal MR> {
|
|
<i>// decode some information into a more convenient format, while providing
|
|
// a nice interface to the user of the "Value" class.</i>
|
|
<b>bit</b> isMod = MR.Value{0};
|
|
<b>bit</b> isRef = MR.Value{1};
|
|
|
|
<i>// other stuff...</i>
|
|
}
|
|
|
|
<i>// Example uses</i>
|
|
<b>def</b> bork : Value<Mod>;
|
|
<b>def</b> zork : Value<Ref>;
|
|
<b>def</b> hork : Value<ModRef>;
|
|
</pre></p>
|
|
|
|
<p>
|
|
This is obviously a contrived example, but it shows how template arguments can
|
|
be used to decouple the interface provided to the user of the class from the
|
|
actual internal data representation expected by the class. In this case,
|
|
running <tt>tblgen</tt> on the example prints the following definitions:</p>
|
|
|
|
<p><pre>
|
|
<b>def</b> bork { <i>// Value</i>
|
|
bit isMod = 1;
|
|
bit isRef = 0;
|
|
}
|
|
<b>def</b> hork { <i>// Value</i>
|
|
bit isMod = 1;
|
|
bit isRef = 1;
|
|
}
|
|
<b>def</b> zork { <i>// Value</i>
|
|
bit isMod = 0;
|
|
bit isRef = 1;
|
|
}
|
|
</pre></p>
|
|
|
|
<p>
|
|
This shows that TableGen was able to dig into the argument and extract a piece
|
|
of information that was requested by the designer of the "Value" class. For
|
|
more realistic examples, please see existing users of TableGen, such as the X86
|
|
backend.</p>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="filescope">File scope entities</tt></a>
|
|
</div>
|
|
|
|
<!----------------------------------------------------------------------------->
|
|
<div class="doc_subsubsection">
|
|
<a name="include">File inclusion</tt></a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
<p>
|
|
TableGen supports the '<tt>include</tt>' token, which textually substitutes the
|
|
specified file in place of the include directive. The filename should be
|
|
specified as a double quoted string immediately after the '<tt>include</tt>'
|
|
keyword. Example:
|
|
|
|
<p><pre>
|
|
<b>include</b> "foo.td"
|
|
</pre></p>
|
|
|
|
</div>
|
|
|
|
<!----------------------------------------------------------------------------->
|
|
<div class="doc_subsubsection">
|
|
<a name="globallet">'let' expressions</tt></a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
<p>
|
|
"let" expressions at file scope are similar to <a href="#recordlet">"let"
|
|
expressions within a record</a>, except they can specify a value binding for
|
|
multiple records at a time, and may be useful in certain other cases.
|
|
File-scope let expressions are really just another way that TableGen allows the
|
|
end-user to factor out commonality from the records.
|
|
</p>
|
|
|
|
<p>
|
|
File-scope "let" expressions take a comma-seperated list of bindings to apply,
|
|
and one of more records to bind the values in. Here are some examples:
|
|
</p>
|
|
|
|
<p><pre>
|
|
<b>let</b> isTerminator = 1, isReturn = 1 <b>in</b>
|
|
<b>def</b> RET : X86Inst<"ret", 0xC3, RawFrm, NoArg>;
|
|
|
|
<b>let</b> isCall = 1 <b>in</b>
|
|
<i>// All calls clobber the non-callee saved registers...</i>
|
|
<b>let</b> Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6] in {
|
|
<b>def</b> CALLpcrel32 : X86Inst<"call", 0xE8, RawFrm, NoArg>;
|
|
<b>def</b> CALLr32 : X86Inst<"call", 0xFF, MRMS2r, Arg32>;
|
|
<b>def</b> CALLm32 : X86Inst<"call", 0xFF, MRMS2m, Arg32>;
|
|
}
|
|
</pre></p>
|
|
|
|
<p>
|
|
File-scope "let" expressions are often useful when a couple of definitions need
|
|
to be added to several records, and the records do not otherwise need to be
|
|
opened, as in the case with the CALL* instructions above.
|
|
</p>
|
|
</div>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"><a name="backends">TableGen backends</a></div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>
|
|
How they work, how to write one. This section should not contain details about
|
|
any particular backend, except maybe -print-enums as an example. This should
|
|
highlight the APIs in TableGen/Record.h.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"><a name="codegenerator">The LLVM code generator</a></div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>
|
|
This is just a temporary, convenient, place to put stuff about the code
|
|
generator before it gets its own document. This should describe all of the
|
|
tablegen backends used by the code generator and the classes/definitions they
|
|
expect.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<hr>
|
|
<div class="doc_footer">
|
|
<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
|
|
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
|
|
<br>
|
|
Last modified: $Date$
|
|
</div>
|
|
|
|
</body>
|
|
</html>
|