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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>
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
53<p>Before you invest a significant amount of effort into a non-trivial
54extension, <span class="doc_warning">ask on the list</span> if what you are
55looking to do can be done with already-existing infrastructure, or if maybe
56someone else is already working on it. You will save yourself a lot of time and
57effort by doing so.</p>
58
59<p>Finally, these are my notes, and since my extensions are not complete, I may
60be missing steps. If you find some omissions, please let me know <a
61href="http://misha.brukman.net/contact.html">directly</a> or post on <a
62href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a>.</p>
63
64</div>
65
66<!-- *********************************************************************** -->
67<div class="doc_section">
68 <a name="instruction">Adding a new instruction</a>
69</div>
70<!-- *********************************************************************** -->
71
72<div class="doc_text">
73
74<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
75format, and will break compatibility with currently-existing LLVM
76installations.</span> Only add an instruction if it is absolutely
77necessary.</p>
78
79<ol>
80<li><tt>llvm/include/llvm/Instruction.def</tt>:
81 add a number for your instruction and an enum name</li>
82
83<li><tt>llvm/include/llvm/i*.h</tt>:
84 add a definition for the class that will represent your instruction</li>
85
86<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
87 add a prototype for a visitor to your new instruction type</li>
88
89<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
90 add a new token to parse your instruction from assembly text file</li>
91
92<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
93 add the grammar on how your instruction can be read and what it will
94 construct as a result</li>
95
96<li><tt>llvm/lib/Bytecode/Reader/InstructionReader.cpp</tt>:
97 add a case for your instruction and how it will be parsed from bytecode</li>
98
99<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
100 add a case for how your instruction will be printed out to assembly</li>
101
102<li><tt>llvm/lib/VMCore/i*.cpp</tt>:
103 implement the class you defined in <tt>llvm/include/llvm/i*.h</tt></li>
104
105</ol>
106
107<p>Also, you need to implement (or modify) any analyses or passes that you want
108to understand this new instruction.</p>
109
110</div>
111
112<!-- *********************************************************************** -->
113<div class="doc_section">
114 <a name="intrinsic">Adding a new intrinsic function</a>
115</div>
116<!-- *********************************************************************** -->
117
118<div class="doc_text">
119
120<p>Adding an intrinsic function is easier than adding an instruction, and is
121transparent to optimization passes which treat it as an unanalyzable function.
122If your added functionality can be expressed as a function call, an intrinsic
123function is the method of choice for LLVM extension.</p>
124
125<ol>
126
127<li><tt>llvm/include/llvm/Intrinsics.h</tt>:
128 add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
129
130<li><tt>llvm/lib/VMCore/IntrinsicLowering.cpp</tt>:
131 implement the lowering for this intrinsic</li>
132
133<li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
134 handle the new intrinsic</li>
135
136<li><tt>llvm/lib/VMCore/Function.cpp</tt>:
137 handle the new intrinsic</li>
138
139</ol>
140
141</div>
142
143<!-- *********************************************************************** -->
144<div class="doc_section">
145 <a name="type">Adding a new type</a>
146</div>
147<!-- *********************************************************************** -->
148
149<div class="doc_text">
150
151<p><span class="doc_warning">WARNING: adding new types changes the bytecode
152format, and will break compatibility with currently-existing LLVM
153installations.</span> Only add new types if it is absolutely necessary.</p>
154
155</div>
156
157<!-- ======================================================================= -->
158<div class="doc_subsection">
159 <a name="fund_type">Adding a fundamental type</a>
160</div>
161
162<div class="doc_text">
163
164<ol>
165
166<li><tt>llvm/include/llvm/Type.def</tt>:
167 add enum for the type</li>
168
169<li><tt>llvm/include/llvm/Type.h</tt>:
170 add ID number for the new type; add static <tt>Type*</tt> for this type</li>
171
172<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
173 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
174 initialize the static <tt>Type*</tt></li>
175
176<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
177 add ability to parse in the type from text assembly</li>
178
179<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
180 add a token for that type</li>
181
182</ol>
183
184</div>
185
186<!-- ======================================================================= -->
187<div class="doc_subsection">
188 <a name="derived_type">Adding a derived type</a>
189</div>
190
191<div class="doc_text">
192
193<p>TODO</p>
194
195</div>
196
197<!-- *********************************************************************** -->
198
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