Gitiles
Code Review Sign In
gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / b3b28275daf8bc16a19880ef3ae458c4de690e47 / . / docs / ExtendingLLVM.html
blob: 7dc8d15dfea883639d52233b10af3340f2e00007 [file] [log] [blame]
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
3<html>
4<head>
5 <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
7</head>
8
9<body>
10
11<div class="doc_title">
12 Extending LLVM: Adding instructions, intrinsics, types, etc.
13</div>
14
15<ol>
16 <li><a href="#introduction">Introduction and Warning</a></li>
17 <li><a href="#instruction">Adding a new instruction</a></li>
18 <li><a href="#intrinsic">Adding a new intrinsic function</a></li>
19 <li><a href="#type">Adding a new type</a>
20 <ol>
21 <li><a href="#fund_type">Adding a new fundamental type</a></li>
22 <li><a href="#derived_type">Adding a new derived type</a></li>
23 </ol></li>
24</ol>
25
26<div class="doc_text">
27 <p><b>Written by <a href="http://misha.brukman.net">Misha Brukman</a></b></p>
28</div>
29
30<!-- *********************************************************************** -->
31<div class="doc_section">
32 <a name="introduction">Introduction and Warning</a>
33</div>
34<!-- *********************************************************************** -->
35
36<div class="doc_text">
37
38<p>During the course of using LLVM, you may wish to customize it for your
39research project or for experimentation. At this point, you may realize that
40you need to add something to LLVM, whether it be a new fundamental type, a new
41intrinsic function, or a whole new instruction.</p>
42
43<p>When you come to this realization, stop and think. Do you really need to
44extend LLVM? Is it a new fundamental capability that LLVM does not support at
45its current incarnation or can it be synthesized from already pre-existing LLVM
46elements? If you are not sure, ask on the <a
47href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a> list. The
48reason is that extending LLVM will get involved as you need to update all the
49different passes that you intend to use with your extension, and there are
50<em>many</em> LLVM analyses and transformations, so it may be quite a bit of
51work.</p>
52
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame^]53<p>Adding an <a href="#intrinsic">intrinsic function</a> is easier than adding
54an instruction, and is transparent to optimization passes which treat it as an
55unanalyzable function. If your added functionality can be expressed as a
56function call, an intrinsic function is the method of choice for LLVM
57extension.</p>
58
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]59<p>Before you invest a significant amount of effort into a non-trivial
60extension, <span class="doc_warning">ask on the list</span> if what you are
61looking to do can be done with already-existing infrastructure, or if maybe
62someone else is already working on it. You will save yourself a lot of time and
63effort by doing so.</p>
64
65<p>Finally, these are my notes, and since my extensions are not complete, I may
66be missing steps. If you find some omissions, please let me know <a
67href="http://misha.brukman.net/contact.html">directly</a> or post on <a
68href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a>.</p>
69
70</div>
71
72<!-- *********************************************************************** -->
73<div class="doc_section">
74 <a name="instruction">Adding a new instruction</a>
75</div>
76<!-- *********************************************************************** -->
77
78<div class="doc_text">
79
80<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame^]81format, and it will take some effort to maintain compatibility with
82the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]83necessary.</p>
84
85<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame^]86
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]87<li><tt>llvm/include/llvm/Instruction.def</tt>:
88 add a number for your instruction and an enum name</li>
89
90<li><tt>llvm/include/llvm/i*.h</tt>:
91 add a definition for the class that will represent your instruction</li>
92
93<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
94 add a prototype for a visitor to your new instruction type</li>
95
96<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
97 add a new token to parse your instruction from assembly text file</li>
98
99<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
100 add the grammar on how your instruction can be read and what it will
101 construct as a result</li>
102
103<li><tt>llvm/lib/Bytecode/Reader/InstructionReader.cpp</tt>:
104 add a case for your instruction and how it will be parsed from bytecode</li>
105
106<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
107 add a case for how your instruction will be printed out to assembly</li>
108
109<li><tt>llvm/lib/VMCore/i*.cpp</tt>:
110 implement the class you defined in <tt>llvm/include/llvm/i*.h</tt></li>
111
112</ol>
113
114<p>Also, you need to implement (or modify) any analyses or passes that you want
115to understand this new instruction.</p>
116
117</div>
118
119<!-- *********************************************************************** -->
120<div class="doc_section">
121 <a name="intrinsic">Adding a new intrinsic function</a>
122</div>
123<!-- *********************************************************************** -->
124
125<div class="doc_text">
126
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]127<ol>
128
129<li><tt>llvm/include/llvm/Intrinsics.h</tt>:
130 add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
131
132<li><tt>llvm/lib/VMCore/IntrinsicLowering.cpp</tt>:
133 implement the lowering for this intrinsic</li>
134
135<li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
136 handle the new intrinsic</li>
137
138<li><tt>llvm/lib/VMCore/Function.cpp</tt>:
139 handle the new intrinsic</li>
140
141</ol>
142
143</div>
144
145<!-- *********************************************************************** -->
146<div class="doc_section">
147 <a name="type">Adding a new type</a>
148</div>
149<!-- *********************************************************************** -->
150
151<div class="doc_text">
152
153<p><span class="doc_warning">WARNING: adding new types changes the bytecode
154format, and will break compatibility with currently-existing LLVM
155installations.</span> Only add new types if it is absolutely necessary.</p>
156
157</div>
158
159<!-- ======================================================================= -->
160<div class="doc_subsection">
161 <a name="fund_type">Adding a fundamental type</a>
162</div>
163
164<div class="doc_text">
165
166<ol>
167
168<li><tt>llvm/include/llvm/Type.def</tt>:
169 add enum for the type</li>
170
171<li><tt>llvm/include/llvm/Type.h</tt>:
172 add ID number for the new type; add static <tt>Type*</tt> for this type</li>
173
174<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
175 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
176 initialize the static <tt>Type*</tt></li>
177
178<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
179 add ability to parse in the type from text assembly</li>
180
181<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
182 add a token for that type</li>
183
184</ol>
185
186</div>
187
188<!-- ======================================================================= -->
189<div class="doc_subsection">
190 <a name="derived_type">Adding a derived type</a>
191</div>
192
193<div class="doc_text">
194
195<p>TODO</p>
196
197</div>
198
199<!-- *********************************************************************** -->
200
201<hr>
202<address>
203 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
204 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
205 <a href="http://validator.w3.org/check/referer"><img
206 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
207
208 <a href="http://misha.brukman.net">Misha Brukman</a><br>
209 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
210 <br>
211 Last modified: $Date$
212</address>
213
214</body>
215</html>