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5 <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
7</head>
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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>
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
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]26<div class="doc_author">
27 <p>Written by <a href="http://misha.brukman.net">Misha Brukman</a></p>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]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
Chris Lattner81519d92004-06-20 07:53:22 +0000[diff] [blame]93<li><tt>llvm/lib/CodeGen/IntrinsicLowering.cpp</tt>:
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]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
Chris Lattner81519d92004-06-20 07:53:22 +0000[diff] [blame]104 not access memory or does not write to memory, add it to the relevant list
Chris Lattner0190fdb2004-04-10 06:56:53 +0000[diff] [blame]105 of functions.</li>
106
Chris Lattnerd828bc62004-04-13 19:48:55 +0000[diff] [blame]107<li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to constant
108 propagate your intrinsic, add support to it in the
109 <tt>canConstantFoldCallTo</tt> and <tt>ConstantFoldCall</tt> functions.</li>
110
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]111<li>Test your intrinsic</li>
112<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
113</ol>
114
115<p>If this intrinsic requires code generator support (ie, it cannot be lowered).
116You should also add support to the code generator in question.</p>
117
118</div>
119
120<!-- *********************************************************************** -->
121<div class="doc_section">
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]122 <a name="instruction">Adding a new instruction</a>
123</div>
124<!-- *********************************************************************** -->
125
126<div class="doc_text">
127
128<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]129format, and it will take some effort to maintain compatibility with
130the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]131necessary.</p>
132
133<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]134
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]135<li><tt>llvm/include/llvm/Instruction.def</tt>:
136 add a number for your instruction and an enum name</li>
137
Misha Brukman47b14a42004-07-29 17:30:56 +0000[diff] [blame]138<li><tt>llvm/include/llvm/Instructions.h</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]139 add a definition for the class that will represent your instruction</li>
140
141<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
142 add a prototype for a visitor to your new instruction type</li>
143
144<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
145 add a new token to parse your instruction from assembly text file</li>
146
147<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
148 add the grammar on how your instruction can be read and what it will
149 construct as a result</li>
150
151<li><tt>llvm/lib/Bytecode/Reader/InstructionReader.cpp</tt>:
152 add a case for your instruction and how it will be parsed from bytecode</li>
153
154<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
155 add a case for how your instruction will be printed out to assembly</li>
156
157<li><tt>llvm/lib/VMCore/i*.cpp</tt>:
158 implement the class you defined in <tt>llvm/include/llvm/i*.h</tt></li>
159
160</ol>
161
162<p>Also, you need to implement (or modify) any analyses or passes that you want
163to understand this new instruction.</p>
164
165</div>
166
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]167
168<!-- *********************************************************************** -->
169<div class="doc_section">
170 <a name="type">Adding a new type</a>
171</div>
172<!-- *********************************************************************** -->
173
174<div class="doc_text">
175
176<p><span class="doc_warning">WARNING: adding new types changes the bytecode
177format, and will break compatibility with currently-existing LLVM
178installations.</span> Only add new types if it is absolutely necessary.</p>
179
180</div>
181
182<!-- ======================================================================= -->
183<div class="doc_subsection">
184 <a name="fund_type">Adding a fundamental type</a>
185</div>
186
187<div class="doc_text">
188
189<ol>
190
191<li><tt>llvm/include/llvm/Type.def</tt>:
192 add enum for the type</li>
193
194<li><tt>llvm/include/llvm/Type.h</tt>:
195 add ID number for the new type; add static <tt>Type*</tt> for this type</li>
196
197<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
198 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
199 initialize the static <tt>Type*</tt></li>
200
201<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
202 add ability to parse in the type from text assembly</li>
203
204<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
205 add a token for that type</li>
206
207</ol>
208
209</div>
210
211<!-- ======================================================================= -->
212<div class="doc_subsection">
213 <a name="derived_type">Adding a derived type</a>
214</div>
215
216<div class="doc_text">
217
218<p>TODO</p>
219
220</div>
221
222<!-- *********************************************************************** -->
223
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231 <a href="http://misha.brukman.net">Misha Brukman</a><br>
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