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5 <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
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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>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]17 <li><a href="#intrinsic">Adding a new intrinsic function</a></li>
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]18 <li><a href="#instruction">Adding a new instruction</a></li>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]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">
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]74 <a name="intrinsic">Adding a new intrinsic function</a>
75</div>
76<!-- *********************************************************************** -->
77
78<div class="doc_text">
79
80<p>Adding a new intrinsic function to LLVM is much easier than adding a new
81instruction. Almost all extensions to LLVM should start as an intrinsic
82function and then be turned into an instruction if warranted.</p>
83
84<ol>
85<li><tt>llvm/docs/LangRef.html</tt>:
86 Document the intrinsic. Decide whether it is code generator specific and
87 what the restrictions are. Talk to other people about it so that you are
88 sure it's a good idea.</li>
89
90<li><tt>llvm/include/llvm/Intrinsics.h</tt>:
91 add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
92
93<li><tt>llvm/lib/VMCore/IntrinsicLowering.cpp</tt>:
94 implement the lowering for this intrinsic</li>
95
96<li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
97 Add code to check the invariants of the intrinsic are respected.</li>
98
99<li><tt>llvm/lib/VMCore/Function.cpp (<tt>Function::getIntrinsicID()</tt>)</tt>:
100 Identify the new intrinsic function, returning the enum for the intrinsic
101 that you added.</li>
Chris Lattner0190fdb2004-04-10 06:56:53 +0000[diff] [blame^]102
103<li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does
104 not access memory, or does not write to memory, add it to the relevant list
105 of functions.</li>
106
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]107<li>Test your intrinsic</li>
108<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
109</ol>
110
111<p>If this intrinsic requires code generator support (ie, it cannot be lowered).
112You should also add support to the code generator in question.</p>
113
114</div>
115
116<!-- *********************************************************************** -->
117<div class="doc_section">
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]118 <a name="instruction">Adding a new instruction</a>
119</div>
120<!-- *********************************************************************** -->
121
122<div class="doc_text">
123
124<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]125format, and it will take some effort to maintain compatibility with
126the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]127necessary.</p>
128
129<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]130
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]131<li><tt>llvm/include/llvm/Instruction.def</tt>:
132 add a number for your instruction and an enum name</li>
133
134<li><tt>llvm/include/llvm/i*.h</tt>:
135 add a definition for the class that will represent your instruction</li>
136
137<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
138 add a prototype for a visitor to your new instruction type</li>
139
140<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
141 add a new token to parse your instruction from assembly text file</li>
142
143<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
144 add the grammar on how your instruction can be read and what it will
145 construct as a result</li>
146
147<li><tt>llvm/lib/Bytecode/Reader/InstructionReader.cpp</tt>:
148 add a case for your instruction and how it will be parsed from bytecode</li>
149
150<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
151 add a case for how your instruction will be printed out to assembly</li>
152
153<li><tt>llvm/lib/VMCore/i*.cpp</tt>:
154 implement the class you defined in <tt>llvm/include/llvm/i*.h</tt></li>
155
156</ol>
157
158<p>Also, you need to implement (or modify) any analyses or passes that you want
159to understand this new instruction.</p>
160
161</div>
162
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]163
164<!-- *********************************************************************** -->
165<div class="doc_section">
166 <a name="type">Adding a new type</a>
167</div>
168<!-- *********************************************************************** -->
169
170<div class="doc_text">
171
172<p><span class="doc_warning">WARNING: adding new types changes the bytecode
173format, and will break compatibility with currently-existing LLVM
174installations.</span> Only add new types if it is absolutely necessary.</p>
175
176</div>
177
178<!-- ======================================================================= -->
179<div class="doc_subsection">
180 <a name="fund_type">Adding a fundamental type</a>
181</div>
182
183<div class="doc_text">
184
185<ol>
186
187<li><tt>llvm/include/llvm/Type.def</tt>:
188 add enum for the type</li>
189
190<li><tt>llvm/include/llvm/Type.h</tt>:
191 add ID number for the new type; add static <tt>Type*</tt> for this type</li>
192
193<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
194 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
195 initialize the static <tt>Type*</tt></li>
196
197<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
198 add ability to parse in the type from text assembly</li>
199
200<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
201 add a token for that type</li>
202
203</ol>
204
205</div>
206
207<!-- ======================================================================= -->
208<div class="doc_subsection">
209 <a name="derived_type">Adding a derived type</a>
210</div>
211
212<div class="doc_text">
213
214<p>TODO</p>
215
216</div>
217
218<!-- *********************************************************************** -->
219
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