llvm-6502/docs/ExtendingLLVM.html
Misha Brukman b3b28275da Incorporated Chris' comments.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12690 91177308-0d34-0410-b5e6-96231b3b80d8
2004-04-06 04:17:51 +00:00

216 lines
7.2 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="#instruction">Adding a new instruction</a></li>
<li><a href="#intrinsic">Adding a new intrinsic function</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_text">
<p><b>Written by <a href="http://misha.brukman.net">Misha Brukman</a></b></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>
<p>Finally, these are my notes, and since my extensions are not complete, I may
be missing steps. If you find some omissions, please let me know <a
href="http://misha.brukman.net/contact.html">directly</a> or post on <a
href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a>.</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/i*.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/InstructionReader.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/i*.cpp</tt>:
implement the class you defined in <tt>llvm/include/llvm/i*.h</tt></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="intrinsic">Adding a new intrinsic function</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<ol>
<li><tt>llvm/include/llvm/Intrinsics.h</tt>:
add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
<li><tt>llvm/lib/VMCore/IntrinsicLowering.cpp</tt>:
implement the lowering for this intrinsic</li>
<li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
handle the new intrinsic</li>
<li><tt>llvm/lib/VMCore/Function.cpp</tt>:
handle the new intrinsic</li>
</ol>
</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.def</tt>:
add enum for the type</li>
<li><tt>llvm/include/llvm/Type.h</tt>:
add ID number 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> =&gt; <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">
<p>TODO</p>
</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://misha.brukman.net">Misha Brukman</a><br>
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
<br>
Last modified: $Date$
</address>
</body>
</html>