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5 <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
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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
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]65</div>
66
67<!-- *********************************************************************** -->
68<div class="doc_section">
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]69 <a name="intrinsic">Adding a new intrinsic function</a>
70</div>
71<!-- *********************************************************************** -->
72
73<div class="doc_text">
74
75<p>Adding a new intrinsic function to LLVM is much easier than adding a new
76instruction. Almost all extensions to LLVM should start as an intrinsic
77function and then be turned into an instruction if warranted.</p>
78
79<ol>
80<li><tt>llvm/docs/LangRef.html</tt>:
81 Document the intrinsic. Decide whether it is code generator specific and
82 what the restrictions are. Talk to other people about it so that you are
83 sure it's a good idea.</li>
84
85<li><tt>llvm/include/llvm/Intrinsics.h</tt>:
86 add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
87
Chris Lattner81519d92004-06-20 07:53:22 +0000[diff] [blame]88<li><tt>llvm/lib/CodeGen/IntrinsicLowering.cpp</tt>:
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]89 implement the lowering for this intrinsic</li>
90
91<li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
92 Add code to check the invariants of the intrinsic are respected.</li>
93
94<li><tt>llvm/lib/VMCore/Function.cpp (<tt>Function::getIntrinsicID()</tt>)</tt>:
95 Identify the new intrinsic function, returning the enum for the intrinsic
96 that you added.</li>
Chris Lattner0190fdb2004-04-10 06:56:53 +0000[diff] [blame]97
98<li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does
Chris Lattner81519d92004-06-20 07:53:22 +0000[diff] [blame]99 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]100 of functions.</li>
101
Chris Lattnerd828bc62004-04-13 19:48:55 +0000[diff] [blame]102<li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to constant
103 propagate your intrinsic, add support to it in the
104 <tt>canConstantFoldCallTo</tt> and <tt>ConstantFoldCall</tt> functions.</li>
105
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]106<li>Test your intrinsic</li>
107<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
108</ol>
109
110<p>If this intrinsic requires code generator support (ie, it cannot be lowered).
111You should also add support to the code generator in question.</p>
112
113</div>
114
115<!-- *********************************************************************** -->
116<div class="doc_section">
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]117 <a name="instruction">Adding a new instruction</a>
118</div>
119<!-- *********************************************************************** -->
120
121<div class="doc_text">
122
123<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]124format, and it will take some effort to maintain compatibility with
125the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]126necessary.</p>
127
128<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]129
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]130<li><tt>llvm/include/llvm/Instruction.def</tt>:
131 add a number for your instruction and an enum name</li>
132
Misha Brukman47b14a42004-07-29 17:30:56 +0000[diff] [blame]133<li><tt>llvm/include/llvm/Instructions.h</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]134 add a definition for the class that will represent your instruction</li>
135
136<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
137 add a prototype for a visitor to your new instruction type</li>
138
139<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
140 add a new token to parse your instruction from assembly text file</li>
141
142<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
143 add the grammar on how your instruction can be read and what it will
144 construct as a result</li>
145
146<li><tt>llvm/lib/Bytecode/Reader/InstructionReader.cpp</tt>:
147 add a case for your instruction and how it will be parsed from bytecode</li>
148
149<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
150 add a case for how your instruction will be printed out to assembly</li>
151
Chris Lattner8f363212004-07-29 17:31:57 +0000[diff] [blame]152<li><tt>llvm/lib/VMCore/Instructions.cpp</tt>:
153 implement the class you defined in <tt>llvm/include/llvm/Instructions.h</tt></li>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]154
155</ol>
156
157<p>Also, you need to implement (or modify) any analyses or passes that you want
158to understand this new instruction.</p>
159
160</div>
161
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]162
163<!-- *********************************************************************** -->
164<div class="doc_section">
165 <a name="type">Adding a new type</a>
166</div>
167<!-- *********************************************************************** -->
168
169<div class="doc_text">
170
171<p><span class="doc_warning">WARNING: adding new types changes the bytecode
172format, and will break compatibility with currently-existing LLVM
173installations.</span> Only add new types if it is absolutely necessary.</p>
174
175</div>
176
177<!-- ======================================================================= -->
178<div class="doc_subsection">
179 <a name="fund_type">Adding a fundamental type</a>
180</div>
181
182<div class="doc_text">
183
184<ol>
185
186<li><tt>llvm/include/llvm/Type.def</tt>:
187 add enum for the type</li>
188
189<li><tt>llvm/include/llvm/Type.h</tt>:
190 add ID number for the new type; add static <tt>Type*</tt> for this type</li>
191
192<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
193 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
194 initialize the static <tt>Type*</tt></li>
195
196<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
197 add ability to parse in the type from text assembly</li>
198
199<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
200 add a token for that type</li>
201
202</ol>
203
204</div>
205
206<!-- ======================================================================= -->
207<div class="doc_subsection">
208 <a name="derived_type">Adding a derived type</a>
209</div>
210
211<div class="doc_text">
212
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]213<ol>
214<li><tt>llvm/include/llvm/Type.def</tt>:
215 add enum for the type</li>
216
217<li><tt>llvm/include/llvm/Type.h</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]218 add ID number for the new type; add a forward declaration of the type
219 also</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]220
221<li><tt>llvm/include/llvm/DerivedType.h</tt>:
222 add new class to represent new class in the hierarchy; add forward
223 declaration to the TypeMap value type</li>
224
225<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
226 add support for derived type to:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]227<div class="doc_code">
228<pre>
229std::string getTypeDescription(const Type &amp;Ty,
230 std::vector&lt;const Type*&gt; &amp;TypeStack)
231bool TypesEqual(const Type *Ty, const Type *Ty2,
232 std::map&lt;const Type*, const Type*&gt; &amp; EqTypes)
233</pre>
234</div>
235 add necessary member functions for type, and factory methods</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]236
237<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
238 add ability to parse in the type from text assembly</li>
239
240<li><tt>llvm/lib/ByteCode/Writer/Writer.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]241 modify <tt>void BytecodeWriter::outputType(const Type *T)</tt> to serialize
242 your type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]243
244<li><tt>llvm/lib/ByteCode/Reader/Reader.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]245 modify <tt>const Type *BytecodeReader::ParseType()</tt> to read your data
246 type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]247
248<li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]249 modify
250<div class="doc_code">
251<pre>
252void calcTypeName(const Type *Ty,
253 std::vector&lt;const Type*&gt; &amp;TypeStack,
254 std::map&lt;const Type*,std::string&gt; &amp;TypeNames,
255 std::string &amp; Result)
256</pre>
257</div>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]258 to output the new derived type
259</li>
260
261
262</ol>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]263
264</div>
265
266<!-- *********************************************************************** -->
267
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