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5 <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
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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">
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
Chris Lattnerd828bc62004-04-13 19:48:55 +0000[diff] [blame]103<li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to constant
104 propagate your intrinsic, add support to it in the
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>
108<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
109</ol>
110
Misha Brukmanad405ce2004-09-27 20:35:59 +0000[diff] [blame]111<p>If this intrinsic requires code generator support (i.e., it cannot be
112lowered), you should also add support to the code generator in question.</p>
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]113
114</div>
115
116<!-- *********************************************************************** -->
117<div class="doc_section">
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]118 <a name="instruction">Adding a new instruction</a>
119</div>
120<!-- *********************************************************************** -->
121
122<div class="doc_text">
123
124<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]125format, and it will take some effort to maintain compatibility with
126the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]127necessary.</p>
128
129<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]130
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]131<li><tt>llvm/include/llvm/Instruction.def</tt>:
132 add a number for your instruction and an enum name</li>
133
Misha Brukman47b14a42004-07-29 17:30:56 +0000[diff] [blame]134<li><tt>llvm/include/llvm/Instructions.h</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]135 add a definition for the class that will represent your instruction</li>
136
137<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
138 add a prototype for a visitor to your new instruction type</li>
139
140<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
141 add a new token to parse your instruction from assembly text file</li>
142
143<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
144 add the grammar on how your instruction can be read and what it will
145 construct as a result</li>
146
147<li><tt>llvm/lib/Bytecode/Reader/InstructionReader.cpp</tt>:
148 add a case for your instruction and how it will be parsed from bytecode</li>
149
150<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
151 add a case for how your instruction will be printed out to assembly</li>
152
Chris Lattner8f363212004-07-29 17:31:57 +0000[diff] [blame]153<li><tt>llvm/lib/VMCore/Instructions.cpp</tt>:
154 implement the class you defined in <tt>llvm/include/llvm/Instructions.h</tt></li>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]155
156</ol>
157
158<p>Also, you need to implement (or modify) any analyses or passes that you want
159to understand this new instruction.</p>
160
161</div>
162
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]163
164<!-- *********************************************************************** -->
165<div class="doc_section">
166 <a name="type">Adding a new type</a>
167</div>
168<!-- *********************************************************************** -->
169
170<div class="doc_text">
171
172<p><span class="doc_warning">WARNING: adding new types changes the bytecode
173format, and will break compatibility with currently-existing LLVM
174installations.</span> Only add new types if it is absolutely necessary.</p>
175
176</div>
177
178<!-- ======================================================================= -->
179<div class="doc_subsection">
180 <a name="fund_type">Adding a fundamental type</a>
181</div>
182
183<div class="doc_text">
184
185<ol>
186
187<li><tt>llvm/include/llvm/Type.def</tt>:
188 add enum for the type</li>
189
190<li><tt>llvm/include/llvm/Type.h</tt>:
191 add ID number for the new type; add static <tt>Type*</tt> for this type</li>
192
193<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
194 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
195 initialize the static <tt>Type*</tt></li>
196
197<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
198 add ability to parse in the type from text assembly</li>
199
200<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
201 add a token for that type</li>
202
203</ol>
204
205</div>
206
207<!-- ======================================================================= -->
208<div class="doc_subsection">
209 <a name="derived_type">Adding a derived type</a>
210</div>
211
212<div class="doc_text">
213
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]214<ol>
215<li><tt>llvm/include/llvm/Type.def</tt>:
216 add enum for the type</li>
217
218<li><tt>llvm/include/llvm/Type.h</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]219 add ID number for the new type; add a forward declaration of the type
220 also</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]221
222<li><tt>llvm/include/llvm/DerivedType.h</tt>:
223 add new class to represent new class in the hierarchy; add forward
224 declaration to the TypeMap value type</li>
225
226<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
227 add support for derived type to:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]228<div class="doc_code">
229<pre>
230std::string getTypeDescription(const Type &amp;Ty,
231 std::vector&lt;const Type*&gt; &amp;TypeStack)
232bool TypesEqual(const Type *Ty, const Type *Ty2,
233 std::map&lt;const Type*, const Type*&gt; &amp; EqTypes)
234</pre>
235</div>
236 add necessary member functions for type, and factory methods</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]237
238<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
239 add ability to parse in the type from text assembly</li>
240
241<li><tt>llvm/lib/ByteCode/Writer/Writer.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]242 modify <tt>void BytecodeWriter::outputType(const Type *T)</tt> to serialize
243 your type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]244
245<li><tt>llvm/lib/ByteCode/Reader/Reader.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]246 modify <tt>const Type *BytecodeReader::ParseType()</tt> to read your data
247 type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]248
249<li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]250 modify
251<div class="doc_code">
252<pre>
253void calcTypeName(const Type *Ty,
254 std::vector&lt;const Type*&gt; &amp;TypeStack,
255 std::map&lt;const Type*,std::string&gt; &amp;TypeNames,
256 std::string &amp; Result)
257</pre>
258</div>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]259 to output the new derived type
260</li>
261
262
263</ol>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]264
265</div>
266
267<!-- *********************************************************************** -->
268
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