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5 <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
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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">
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame^]27 <p>Written by <a href="http://misha.brukman.net">Misha Brukman</a>,
28 Brad Jones, and <a href="http://nondot.org/sabre">Chris Lattner</a></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 Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]89<li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
90 Add code to check the invariants of the intrinsic are respected.</li>
91
92<li><tt>llvm/lib/VMCore/Function.cpp (<tt>Function::getIntrinsicID()</tt>)</tt>:
93 Identify the new intrinsic function, returning the enum for the intrinsic
94 that you added.</li>
Chris Lattner0190fdb2004-04-10 06:56:53 +0000[diff] [blame]95
96<li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does
Chris Lattner81519d92004-06-20 07:53:22 +0000[diff] [blame]97 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]98 of functions.</li>
99
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame^]100<li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to constant
101fold your intrinsic, add support to it in the <tt>canConstantFoldCallTo</tt> and
102<tt>ConstantFoldCall</tt> functions.</li>
Chris Lattnerd828bc62004-04-13 19:48:55 +0000[diff] [blame]103
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]104<li>Test your intrinsic</li>
Misha Brukmana4242282004-12-01 20:58:54 +0000[diff] [blame]105
106<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]107</ol>
108
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame^]109<p>Once the intrinsic has been added to the system, you must add code generator
110support for it. Generally you must do the following steps:</p>
111
112<dl>
113<dt>Add support to the C backend in <tt>lib/Target/CBackend/</tt></dt>
114
115<dd>Depending on the intrinsic, there are a few ways to implement this. First,
116if it makes sense to lower the intrinsic to an expanded sequence of C code in
117all cases, just emit the expansion in <tt>visitCallInst</tt>. Second, if the
118intrinsic has some way to express it with GCC (or any other compiler)
119extensions, it can be conditionally supported based on the compiler compiling
120the CBE output (see llvm.prefetch for an example). Third, if the intrinsic
121really has no way to be lowered, just have the code generator emit code that
122prints an error message and calls abort if executed.
123</dd>
124
125<dt>Add a enum value for the SelectionDAG node in
126<tt>include/llvm/CodeGen/SelectionDAGNodes.h</tt></dt>
127
128<dd>Also, add code to <tt>lib/CodeGen/SelectionDAG/SelectionDAG.cpp</tt> (and
129<tt>SelectionDAGPrinter.cpp</tt>) to print the node.</dd>
130
131<dt>Add code to <tt>SelectionDAG/SelectionDAGISel.cpp</tt> to recognize the
132intrinsic.</dt>
133
134<dd>Presumably the intrinsic should be recognized and turned into the node you
135added above.</dd>
136
137<dt>Add code to <tt>SelectionDAG/LegalizeDAG.cpp</tt> to <a
138href="CodeGenerator.html#selectiondag_legalize">legalize, promote, and
139expand</a> the node as necessary.</dt>
140
141<dd>If the intrinsic can be expanded to primitive operations, legalize can break
142the node down into other elementary operations that are be supported.</dd>
143
144<dt>Add target-specific support to specific code generators.</dt>
145
146<dd>Extend the code generators you are interested in to recognize and support
147the node, emitting the code you want.</dd>
148</dl>
149
150<p>
151Unfortunately, the process of extending the code generator to support a new node
152is not extremely well documented. As such, it is often helpful to look at other
153intrinsics (e.g. <tt>llvm.ctpop</tt>) to see how they are recognized and turned
154into a node by <tt>SelectionDAGISel.cpp</tt>, legalized by
155<tt>LegalizeDAG.cpp</tt>, then finally emitted by the various code generators.
156</p>
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]157
158</div>
159
160<!-- *********************************************************************** -->
161<div class="doc_section">
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]162 <a name="instruction">Adding a new instruction</a>
163</div>
164<!-- *********************************************************************** -->
165
166<div class="doc_text">
167
168<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]169format, and it will take some effort to maintain compatibility with
170the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]171necessary.</p>
172
173<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]174
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]175<li><tt>llvm/include/llvm/Instruction.def</tt>:
176 add a number for your instruction and an enum name</li>
177
Misha Brukman47b14a42004-07-29 17:30:56 +0000[diff] [blame]178<li><tt>llvm/include/llvm/Instructions.h</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]179 add a definition for the class that will represent your instruction</li>
180
181<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
182 add a prototype for a visitor to your new instruction type</li>
183
184<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
185 add a new token to parse your instruction from assembly text file</li>
186
187<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
188 add the grammar on how your instruction can be read and what it will
189 construct as a result</li>
190
Misha Brukmane39cd632004-09-28 16:58:12 +0000[diff] [blame]191<li><tt>llvm/lib/Bytecode/Reader/Reader.cpp</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]192 add a case for your instruction and how it will be parsed from bytecode</li>
193
194<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
195 add a case for how your instruction will be printed out to assembly</li>
196
Chris Lattner8f363212004-07-29 17:31:57 +0000[diff] [blame]197<li><tt>llvm/lib/VMCore/Instructions.cpp</tt>:
Misha Brukmane39cd632004-09-28 16:58:12 +0000[diff] [blame]198 implement the class you defined in
199 <tt>llvm/include/llvm/Instructions.h</tt></li>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]200
Misha Brukmana4242282004-12-01 20:58:54 +0000[diff] [blame]201<li>Test your instruction</li>
202
203<li><tt>llvm/lib/Target/*</tt>:
204 Add support for your instruction to code generators, or add a lowering
205 pass.</li>
206
207<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
208
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]209</ol>
210
211<p>Also, you need to implement (or modify) any analyses or passes that you want
212to understand this new instruction.</p>
213
214</div>
215
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]216
217<!-- *********************************************************************** -->
218<div class="doc_section">
219 <a name="type">Adding a new type</a>
220</div>
221<!-- *********************************************************************** -->
222
223<div class="doc_text">
224
225<p><span class="doc_warning">WARNING: adding new types changes the bytecode
226format, and will break compatibility with currently-existing LLVM
227installations.</span> Only add new types if it is absolutely necessary.</p>
228
229</div>
230
231<!-- ======================================================================= -->
232<div class="doc_subsection">
233 <a name="fund_type">Adding a fundamental type</a>
234</div>
235
236<div class="doc_text">
237
238<ol>
239
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]240<li><tt>llvm/include/llvm/Type.h</tt>:
Chris Lattner55f95012005-04-23 21:59:11 +0000[diff] [blame]241 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]242
243<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
244 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
245 initialize the static <tt>Type*</tt></li>
246
247<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
248 add ability to parse in the type from text assembly</li>
249
250<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
251 add a token for that type</li>
252
253</ol>
254
255</div>
256
257<!-- ======================================================================= -->
258<div class="doc_subsection">
259 <a name="derived_type">Adding a derived type</a>
260</div>
261
262<div class="doc_text">
263
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]264<ol>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]265<li><tt>llvm/include/llvm/Type.h</tt>:
Chris Lattner55f95012005-04-23 21:59:11 +0000[diff] [blame]266 add enum for the new type; add a forward declaration of the type
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]267 also</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]268
269<li><tt>llvm/include/llvm/DerivedType.h</tt>:
270 add new class to represent new class in the hierarchy; add forward
271 declaration to the TypeMap value type</li>
272
273<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
274 add support for derived type to:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]275<div class="doc_code">
276<pre>
277std::string getTypeDescription(const Type &amp;Ty,
278 std::vector&lt;const Type*&gt; &amp;TypeStack)
279bool TypesEqual(const Type *Ty, const Type *Ty2,
280 std::map&lt;const Type*, const Type*&gt; &amp; EqTypes)
281</pre>
282</div>
283 add necessary member functions for type, and factory methods</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]284
285<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
286 add ability to parse in the type from text assembly</li>
287
288<li><tt>llvm/lib/ByteCode/Writer/Writer.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]289 modify <tt>void BytecodeWriter::outputType(const Type *T)</tt> to serialize
290 your type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]291
292<li><tt>llvm/lib/ByteCode/Reader/Reader.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]293 modify <tt>const Type *BytecodeReader::ParseType()</tt> to read your data
294 type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]295
296<li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]297 modify
298<div class="doc_code">
299<pre>
300void calcTypeName(const Type *Ty,
301 std::vector&lt;const Type*&gt; &amp;TypeStack,
302 std::map&lt;const Type*,std::string&gt; &amp;TypeNames,
303 std::string &amp; Result)
304</pre>
305</div>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]306 to output the new derived type
307</li>
308
309
310</ol>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]311
312</div>
313
314<!-- *********************************************************************** -->
315
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