docs/ExtendingLLVM.html - fp2-dev/platform/external/llvm - Gitiles

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   <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
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 <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>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 will break compatibility with currently-existing LLVM
 installations.</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">

 <p>Adding an intrinsic function 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>

 <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
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   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>
	<!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>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 will break compatibility with currently-existing LLVM
	installations.</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">

	<p>Adding an intrinsic function 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>

	<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> => <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>
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	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>

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