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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 36365406352b15fd3747ef5c6efd85ded4e04608 / . / docs / ExtendingLLVM.html
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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>
102<li>Test your intrinsic</li>
103<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
104</ol>
105
106<p>If this intrinsic requires code generator support (ie, it cannot be lowered).
107You should also add support to the code generator in question.</p>
108
109</div>
110
111<!-- *********************************************************************** -->
112<div class="doc_section">
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]113 <a name="instruction">Adding a new instruction</a>
114</div>
115<!-- *********************************************************************** -->
116
117<div class="doc_text">
118
119<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]120format, and it will take some effort to maintain compatibility with
121the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]122necessary.</p>
123
124<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]125
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]126<li><tt>llvm/include/llvm/Instruction.def</tt>:
127 add a number for your instruction and an enum name</li>
128
129<li><tt>llvm/include/llvm/i*.h</tt>:
130 add a definition for the class that will represent your instruction</li>
131
132<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
133 add a prototype for a visitor to your new instruction type</li>
134
135<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
136 add a new token to parse your instruction from assembly text file</li>
137
138<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
139 add the grammar on how your instruction can be read and what it will
140 construct as a result</li>
141
142<li><tt>llvm/lib/Bytecode/Reader/InstructionReader.cpp</tt>:
143 add a case for your instruction and how it will be parsed from bytecode</li>
144
145<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
146 add a case for how your instruction will be printed out to assembly</li>
147
148<li><tt>llvm/lib/VMCore/i*.cpp</tt>:
149 implement the class you defined in <tt>llvm/include/llvm/i*.h</tt></li>
150
151</ol>
152
153<p>Also, you need to implement (or modify) any analyses or passes that you want
154to understand this new instruction.</p>
155
156</div>
157
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]158
159<!-- *********************************************************************** -->
160<div class="doc_section">
161 <a name="type">Adding a new type</a>
162</div>
163<!-- *********************************************************************** -->
164
165<div class="doc_text">
166
167<p><span class="doc_warning">WARNING: adding new types changes the bytecode
168format, and will break compatibility with currently-existing LLVM
169installations.</span> Only add new types if it is absolutely necessary.</p>
170
171</div>
172
173<!-- ======================================================================= -->
174<div class="doc_subsection">
175 <a name="fund_type">Adding a fundamental type</a>
176</div>
177
178<div class="doc_text">
179
180<ol>
181
182<li><tt>llvm/include/llvm/Type.def</tt>:
183 add enum for the type</li>
184
185<li><tt>llvm/include/llvm/Type.h</tt>:
186 add ID number for the new type; add static <tt>Type*</tt> for this type</li>
187
188<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
189 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
190 initialize the static <tt>Type*</tt></li>
191
192<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
193 add ability to parse in the type from text assembly</li>
194
195<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
196 add a token for that type</li>
197
198</ol>
199
200</div>
201
202<!-- ======================================================================= -->
203<div class="doc_subsection">
204 <a name="derived_type">Adding a derived type</a>
205</div>
206
207<div class="doc_text">
208
209<p>TODO</p>
210
211</div>
212
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