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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>
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">
Misha Brukman39dccd82004-09-21 16:53:29 +0000[diff] [blame]27 <p>Written by <a href="http://misha.brukman.net">Misha Brukman</a> and
28 Brad Jones</p>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]29</div>
30
31<!-- *********************************************************************** -->
32<div class="doc_section">
33 <a name="introduction">Introduction and Warning</a>
34</div>
35<!-- *********************************************************************** -->
36
37<div class="doc_text">
38
39<p>During the course of using LLVM, you may wish to customize it for your
40research project or for experimentation. At this point, you may realize that
41you need to add something to LLVM, whether it be a new fundamental type, a new
42intrinsic function, or a whole new instruction.</p>
43
44<p>When you come to this realization, stop and think. Do you really need to
45extend LLVM? Is it a new fundamental capability that LLVM does not support at
46its current incarnation or can it be synthesized from already pre-existing LLVM
47elements? If you are not sure, ask on the <a
48href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a> list. The
49reason is that extending LLVM will get involved as you need to update all the
50different passes that you intend to use with your extension, and there are
51<em>many</em> LLVM analyses and transformations, so it may be quite a bit of
52work.</p>
53
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]54<p>Adding an <a href="#intrinsic">intrinsic function</a> is easier than adding
55an instruction, and is transparent to optimization passes which treat it as an
56unanalyzable function. If your added functionality can be expressed as a
57function call, an intrinsic function is the method of choice for LLVM
58extension.</p>
59
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]60<p>Before you invest a significant amount of effort into a non-trivial
61extension, <span class="doc_warning">ask on the list</span> if what you are
62looking to do can be done with already-existing infrastructure, or if maybe
63someone else is already working on it. You will save yourself a lot of time and
64effort by doing so.</p>
65
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]66</div>
67
68<!-- *********************************************************************** -->
69<div class="doc_section">
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]70 <a name="intrinsic">Adding a new intrinsic function</a>
71</div>
72<!-- *********************************************************************** -->
73
74<div class="doc_text">
75
76<p>Adding a new intrinsic function to LLVM is much easier than adding a new
77instruction. Almost all extensions to LLVM should start as an intrinsic
78function and then be turned into an instruction if warranted.</p>
79
80<ol>
81<li><tt>llvm/docs/LangRef.html</tt>:
82 Document the intrinsic. Decide whether it is code generator specific and
83 what the restrictions are. Talk to other people about it so that you are
84 sure it's a good idea.</li>
85
86<li><tt>llvm/include/llvm/Intrinsics.h</tt>:
87 add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
88
Chris Lattner81519d92004-06-20 07:53:22 +0000[diff] [blame]89<li><tt>llvm/lib/CodeGen/IntrinsicLowering.cpp</tt>:
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]90 implement the lowering for this intrinsic</li>
91
92<li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
93 Add code to check the invariants of the intrinsic are respected.</li>
94
95<li><tt>llvm/lib/VMCore/Function.cpp (<tt>Function::getIntrinsicID()</tt>)</tt>:
96 Identify the new intrinsic function, returning the enum for the intrinsic
97 that you added.</li>
Chris Lattner0190fdb2004-04-10 06:56:53 +0000[diff] [blame]98
99<li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does
Chris Lattner81519d92004-06-20 07:53:22 +0000[diff] [blame]100 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]101 of functions.</li>
102
Misha Brukmana4242282004-12-01 20:58:54 +0000[diff] [blame]103<li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to
104 constant-propagate your intrinsic, add support to it in the
Chris Lattnerd828bc62004-04-13 19:48:55 +0000[diff] [blame]105 <tt>canConstantFoldCallTo</tt> and <tt>ConstantFoldCall</tt> functions.</li>
106
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]107<li>Test your intrinsic</li>
Misha Brukmana4242282004-12-01 20:58:54 +0000[diff] [blame]108
109<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite</li>
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]110</ol>
111
Misha Brukmanad405ce2004-09-27 20:35:59 +0000[diff] [blame]112<p>If this intrinsic requires code generator support (i.e., it cannot be
113lowered), you should also add support to the code generator in question.</p>
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]114
115</div>
116
117<!-- *********************************************************************** -->
118<div class="doc_section">
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]119 <a name="instruction">Adding a new instruction</a>
120</div>
121<!-- *********************************************************************** -->
122
123<div class="doc_text">
124
125<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]126format, and it will take some effort to maintain compatibility with
127the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]128necessary.</p>
129
130<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]131
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]132<li><tt>llvm/include/llvm/Instruction.def</tt>:
133 add a number for your instruction and an enum name</li>
134
Misha Brukman47b14a42004-07-29 17:30:56 +0000[diff] [blame]135<li><tt>llvm/include/llvm/Instructions.h</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]136 add a definition for the class that will represent your instruction</li>
137
138<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
139 add a prototype for a visitor to your new instruction type</li>
140
141<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
142 add a new token to parse your instruction from assembly text file</li>
143
144<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
145 add the grammar on how your instruction can be read and what it will
146 construct as a result</li>
147
Misha Brukmane39cd632004-09-28 16:58:12 +0000[diff] [blame]148<li><tt>llvm/lib/Bytecode/Reader/Reader.cpp</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]149 add a case for your instruction and how it will be parsed from bytecode</li>
150
151<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
152 add a case for how your instruction will be printed out to assembly</li>
153
Chris Lattner8f363212004-07-29 17:31:57 +0000[diff] [blame]154<li><tt>llvm/lib/VMCore/Instructions.cpp</tt>:
Misha Brukmane39cd632004-09-28 16:58:12 +0000[diff] [blame]155 implement the class you defined in
156 <tt>llvm/include/llvm/Instructions.h</tt></li>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]157
Misha Brukmana4242282004-12-01 20:58:54 +0000[diff] [blame]158<li>Test your instruction</li>
159
160<li><tt>llvm/lib/Target/*</tt>:
161 Add support for your instruction to code generators, or add a lowering
162 pass.</li>
163
164<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
165
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]166</ol>
167
168<p>Also, you need to implement (or modify) any analyses or passes that you want
169to understand this new instruction.</p>
170
171</div>
172
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]173
174<!-- *********************************************************************** -->
175<div class="doc_section">
176 <a name="type">Adding a new type</a>
177</div>
178<!-- *********************************************************************** -->
179
180<div class="doc_text">
181
182<p><span class="doc_warning">WARNING: adding new types changes the bytecode
183format, and will break compatibility with currently-existing LLVM
184installations.</span> Only add new types if it is absolutely necessary.</p>
185
186</div>
187
188<!-- ======================================================================= -->
189<div class="doc_subsection">
190 <a name="fund_type">Adding a fundamental type</a>
191</div>
192
193<div class="doc_text">
194
195<ol>
196
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]197<li><tt>llvm/include/llvm/Type.h</tt>:
Chris Lattner55f95012005-04-23 21:59:11 +0000[diff] [blame^]198 add enum for the new type; add static <tt>Type*</tt> for this type</li>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]199
200<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
201 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
202 initialize the static <tt>Type*</tt></li>
203
204<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
205 add ability to parse in the type from text assembly</li>
206
207<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
208 add a token for that type</li>
209
210</ol>
211
212</div>
213
214<!-- ======================================================================= -->
215<div class="doc_subsection">
216 <a name="derived_type">Adding a derived type</a>
217</div>
218
219<div class="doc_text">
220
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]221<ol>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]222<li><tt>llvm/include/llvm/Type.h</tt>:
Chris Lattner55f95012005-04-23 21:59:11 +0000[diff] [blame^]223 add enum for the new type; add a forward declaration of the type
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]224 also</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]225
226<li><tt>llvm/include/llvm/DerivedType.h</tt>:
227 add new class to represent new class in the hierarchy; add forward
228 declaration to the TypeMap value type</li>
229
230<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
231 add support for derived type to:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]232<div class="doc_code">
233<pre>
234std::string getTypeDescription(const Type &amp;Ty,
235 std::vector&lt;const Type*&gt; &amp;TypeStack)
236bool TypesEqual(const Type *Ty, const Type *Ty2,
237 std::map&lt;const Type*, const Type*&gt; &amp; EqTypes)
238</pre>
239</div>
240 add necessary member functions for type, and factory methods</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]241
242<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
243 add ability to parse in the type from text assembly</li>
244
245<li><tt>llvm/lib/ByteCode/Writer/Writer.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]246 modify <tt>void BytecodeWriter::outputType(const Type *T)</tt> to serialize
247 your type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]248
249<li><tt>llvm/lib/ByteCode/Reader/Reader.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]250 modify <tt>const Type *BytecodeReader::ParseType()</tt> to read your data
251 type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]252
253<li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]254 modify
255<div class="doc_code">
256<pre>
257void calcTypeName(const Type *Ty,
258 std::vector&lt;const Type*&gt; &amp;TypeStack,
259 std::map&lt;const Type*,std::string&gt; &amp;TypeNames,
260 std::string &amp; Result)
261</pre>
262</div>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]263 to output the new derived type
264</li>
265
266
267</ol>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]268
269</div>
270
271<!-- *********************************************************************** -->
272
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