forked from OSchip/llvm-project
330 lines
12 KiB
HTML
330 lines
12 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
|
|
"http://www.w3.org/TR/html4/strict.dtd">
|
|
<html>
|
|
<head>
|
|
<title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
|
|
<link rel="stylesheet" href="llvm.css" type="text/css">
|
|
</head>
|
|
|
|
<body>
|
|
|
|
<div class="doc_title">
|
|
Extending LLVM: Adding instructions, intrinsics, types, etc.
|
|
</div>
|
|
|
|
<ol>
|
|
<li><a href="#introduction">Introduction and Warning</a></li>
|
|
<li><a href="#intrinsic">Adding a new intrinsic function</a></li>
|
|
<li><a href="#instruction">Adding a new instruction</a></li>
|
|
<li><a href="#type">Adding a new type</a>
|
|
<ol>
|
|
<li><a href="#fund_type">Adding a new fundamental type</a></li>
|
|
<li><a href="#derived_type">Adding a new derived type</a></li>
|
|
</ol></li>
|
|
</ol>
|
|
|
|
<div class="doc_author">
|
|
<p>Written by <a href="http://misha.brukman.net">Misha Brukman</a>,
|
|
Brad Jones, and <a href="http://nondot.org/sabre">Chris Lattner</a></p>
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="introduction">Introduction and Warning</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>During the course of using LLVM, you may wish to customize it for your
|
|
research project or for experimentation. At this point, you may realize that
|
|
you need to add something to LLVM, whether it be a new fundamental type, a new
|
|
intrinsic function, or a whole new instruction.</p>
|
|
|
|
<p>When you come to this realization, stop and think. Do you really need to
|
|
extend LLVM? Is it a new fundamental capability that LLVM does not support at
|
|
its current incarnation or can it be synthesized from already pre-existing LLVM
|
|
elements? If you are not sure, ask on the <a
|
|
href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a> list. The
|
|
reason is that extending LLVM will get involved as you need to update all the
|
|
different passes that you intend to use with your extension, and there are
|
|
<em>many</em> LLVM analyses and transformations, so it may be quite a bit of
|
|
work.</p>
|
|
|
|
<p>Adding an <a href="#intrinsic">intrinsic function</a> is easier than adding
|
|
an instruction, and is transparent to optimization passes which treat it as an
|
|
unanalyzable function. If your added functionality can be expressed as a
|
|
function call, an intrinsic function is the method of choice for LLVM
|
|
extension.</p>
|
|
|
|
<p>Before you invest a significant amount of effort into a non-trivial
|
|
extension, <span class="doc_warning">ask on the list</span> if what you are
|
|
looking to do can be done with already-existing infrastructure, or if maybe
|
|
someone else is already working on it. You will save yourself a lot of time and
|
|
effort by doing so.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="intrinsic">Adding a new intrinsic function</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Adding a new intrinsic function to LLVM is much easier than adding a new
|
|
instruction. Almost all extensions to LLVM should start as an intrinsic
|
|
function and then be turned into an instruction if warranted.</p>
|
|
|
|
<ol>
|
|
<li><tt>llvm/docs/LangRef.html</tt>:
|
|
Document the intrinsic. Decide whether it is code generator specific and
|
|
what the restrictions are. Talk to other people about it so that you are
|
|
sure it's a good idea.</li>
|
|
|
|
<li><tt>llvm/include/llvm/Intrinsics.h</tt>:
|
|
add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
|
|
|
|
<li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
|
|
Add code to check the invariants of the intrinsic are respected.</li>
|
|
|
|
<li><tt>llvm/lib/VMCore/Function.cpp (<tt>Function::getIntrinsicID()</tt>)</tt>:
|
|
Identify the new intrinsic function, returning the enum for the intrinsic
|
|
that you added.</li>
|
|
|
|
<li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does
|
|
not access memory or does not write to memory, add it to the relevant list
|
|
of functions.</li>
|
|
|
|
<li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to constant
|
|
fold your intrinsic, add support to it in the <tt>canConstantFoldCallTo</tt> and
|
|
<tt>ConstantFoldCall</tt> functions.</li>
|
|
|
|
<li>Test your intrinsic</li>
|
|
|
|
<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite</li>
|
|
</ol>
|
|
|
|
<p>Once the intrinsic has been added to the system, you must add code generator
|
|
support for it. Generally you must do the following steps:</p>
|
|
|
|
<dl>
|
|
<dt>Add support to the C backend in <tt>lib/Target/CBackend/</tt></dt>
|
|
|
|
<dd>Depending on the intrinsic, there are a few ways to implement this. First,
|
|
if it makes sense to lower the intrinsic to an expanded sequence of C code in
|
|
all cases, just emit the expansion in <tt>visitCallInst</tt>. Second, if the
|
|
intrinsic has some way to express it with GCC (or any other compiler)
|
|
extensions, it can be conditionally supported based on the compiler compiling
|
|
the CBE output (see llvm.prefetch for an example). Third, if the intrinsic
|
|
really has no way to be lowered, just have the code generator emit code that
|
|
prints an error message and calls abort if executed.
|
|
</dd>
|
|
|
|
<dt>Add a enum value for the SelectionDAG node in
|
|
<tt>include/llvm/CodeGen/SelectionDAGNodes.h</tt></dt>
|
|
|
|
<dd>Also, add code to <tt>lib/CodeGen/SelectionDAG/SelectionDAG.cpp</tt> (and
|
|
<tt>SelectionDAGPrinter.cpp</tt>) to print the node.</dd>
|
|
|
|
<dt>Add code to <tt>SelectionDAG/SelectionDAGISel.cpp</tt> to recognize the
|
|
intrinsic.</dt>
|
|
|
|
<dd>Presumably the intrinsic should be recognized and turned into the node you
|
|
added above.</dd>
|
|
|
|
<dt>Add code to <tt>SelectionDAG/LegalizeDAG.cpp</tt> to <a
|
|
href="CodeGenerator.html#selectiondag_legalize">legalize, promote, and
|
|
expand</a> the node as necessary.</dt>
|
|
|
|
<dd>If the intrinsic can be expanded to primitive operations, legalize can break
|
|
the node down into other elementary operations that are be supported.</dd>
|
|
|
|
<dt>Add target-specific support to specific code generators.</dt>
|
|
|
|
<dd>Extend the code generators you are interested in to recognize and support
|
|
the node, emitting the code you want.</dd>
|
|
</dl>
|
|
|
|
<p>
|
|
Unfortunately, the process of extending the code generator to support a new node
|
|
is not extremely well documented. As such, it is often helpful to look at other
|
|
intrinsics (e.g. <tt>llvm.ctpop</tt>) to see how they are recognized and turned
|
|
into a node by <tt>SelectionDAGISel.cpp</tt>, legalized by
|
|
<tt>LegalizeDAG.cpp</tt>, then finally emitted by the various code generators.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="instruction">Adding a new instruction</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
|
|
format, and it will take some effort to maintain compatibility with
|
|
the previous version.</span> Only add an instruction if it is absolutely
|
|
necessary.</p>
|
|
|
|
<ol>
|
|
|
|
<li><tt>llvm/include/llvm/Instruction.def</tt>:
|
|
add a number for your instruction and an enum name</li>
|
|
|
|
<li><tt>llvm/include/llvm/Instructions.h</tt>:
|
|
add a definition for the class that will represent your instruction</li>
|
|
|
|
<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
|
|
add a prototype for a visitor to your new instruction type</li>
|
|
|
|
<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
|
|
add a new token to parse your instruction from assembly text file</li>
|
|
|
|
<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
|
|
add the grammar on how your instruction can be read and what it will
|
|
construct as a result</li>
|
|
|
|
<li><tt>llvm/lib/Bytecode/Reader/Reader.cpp</tt>:
|
|
add a case for your instruction and how it will be parsed from bytecode</li>
|
|
|
|
<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
|
|
add a case for how your instruction will be printed out to assembly</li>
|
|
|
|
<li><tt>llvm/lib/VMCore/Instructions.cpp</tt>:
|
|
implement the class you defined in
|
|
<tt>llvm/include/llvm/Instructions.h</tt></li>
|
|
|
|
<li>Test your instruction</li>
|
|
|
|
<li><tt>llvm/lib/Target/*</tt>:
|
|
Add support for your instruction to code generators, or add a lowering
|
|
pass.</li>
|
|
|
|
<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
|
|
|
|
</ol>
|
|
|
|
<p>Also, you need to implement (or modify) any analyses or passes that you want
|
|
to understand this new instruction.</p>
|
|
|
|
</div>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="type">Adding a new type</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p><span class="doc_warning">WARNING: adding new types changes the bytecode
|
|
format, and will break compatibility with currently-existing LLVM
|
|
installations.</span> Only add new types if it is absolutely necessary.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="fund_type">Adding a fundamental type</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ol>
|
|
|
|
<li><tt>llvm/include/llvm/Type.h</tt>:
|
|
add enum for the new type; add static <tt>Type*</tt> for this type</li>
|
|
|
|
<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
|
|
add mapping from <tt>TypeID</tt> => <tt>Type*</tt>;
|
|
initialize the static <tt>Type*</tt></li>
|
|
|
|
<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
|
|
add ability to parse in the type from text assembly</li>
|
|
|
|
<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
|
|
add a token for that type</li>
|
|
|
|
</ol>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="derived_type">Adding a derived type</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ol>
|
|
<li><tt>llvm/include/llvm/Type.h</tt>:
|
|
add enum for the new type; add a forward declaration of the type
|
|
also</li>
|
|
|
|
<li><tt>llvm/include/llvm/DerivedType.h</tt>:
|
|
add new class to represent new class in the hierarchy; add forward
|
|
declaration to the TypeMap value type</li>
|
|
|
|
<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
|
|
add support for derived type to:
|
|
<div class="doc_code">
|
|
<pre>
|
|
std::string getTypeDescription(const Type &Ty,
|
|
std::vector<const Type*> &TypeStack)
|
|
bool TypesEqual(const Type *Ty, const Type *Ty2,
|
|
std::map<const Type*, const Type*> & EqTypes)
|
|
</pre>
|
|
</div>
|
|
add necessary member functions for type, and factory methods</li>
|
|
|
|
<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
|
|
add ability to parse in the type from text assembly</li>
|
|
|
|
<li><tt>llvm/lib/ByteCode/Writer/Writer.cpp</tt>:
|
|
modify <tt>void BytecodeWriter::outputType(const Type *T)</tt> to serialize
|
|
your type</li>
|
|
|
|
<li><tt>llvm/lib/ByteCode/Reader/Reader.cpp</tt>:
|
|
modify <tt>const Type *BytecodeReader::ParseType()</tt> to read your data
|
|
type</li>
|
|
|
|
<li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>:
|
|
modify
|
|
<div class="doc_code">
|
|
<pre>
|
|
void calcTypeName(const Type *Ty,
|
|
std::vector<const Type*> &TypeStack,
|
|
std::map<const Type*,std::string> &TypeNames,
|
|
std::string & Result)
|
|
</pre>
|
|
</div>
|
|
to output the new derived type
|
|
</li>
|
|
|
|
|
|
</ol>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
<hr>
|
|
<address>
|
|
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
|
|
src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
|
|
<a href="http://validator.w3.org/check/referer"><img
|
|
src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
|
|
|
|
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
|
|
<br>
|
|
Last modified: $Date$
|
|
</address>
|
|
|
|
</body>
|
|
</html>
|