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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>
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]19 <li><a href="#sdnode">Adding a new SelectionDAG node</a></li>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]20 <li><a href="#type">Adding a new type</a>
21 <ol>
22 <li><a href="#fund_type">Adding a new fundamental type</a></li>
23 <li><a href="#derived_type">Adding a new derived type</a></li>
24 </ol></li>
25</ol>
26
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]27<div class="doc_author">
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]28 <p>Written by <a href="http://misha.brukman.net">Misha Brukman</a>,
Chris Lattnerb5f6e252006-01-16 16:31:40 +0000[diff] [blame]29 Brad Jones, Nate Begeman,
30 and <a href="http://nondot.org/sabre">Chris Lattner</a></p>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]31</div>
32
33<!-- *********************************************************************** -->
34<div class="doc_section">
35 <a name="introduction">Introduction and Warning</a>
36</div>
37<!-- *********************************************************************** -->
38
39<div class="doc_text">
40
41<p>During the course of using LLVM, you may wish to customize it for your
42research project or for experimentation. At this point, you may realize that
43you need to add something to LLVM, whether it be a new fundamental type, a new
44intrinsic function, or a whole new instruction.</p>
45
46<p>When you come to this realization, stop and think. Do you really need to
47extend LLVM? Is it a new fundamental capability that LLVM does not support at
48its current incarnation or can it be synthesized from already pre-existing LLVM
49elements? If you are not sure, ask on the <a
50href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a> list. The
51reason is that extending LLVM will get involved as you need to update all the
52different passes that you intend to use with your extension, and there are
53<em>many</em> LLVM analyses and transformations, so it may be quite a bit of
54work.</p>
55
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]56<p>Adding an <a href="#intrinsic">intrinsic function</a> is easier than adding
57an instruction, and is transparent to optimization passes which treat it as an
58unanalyzable function. If your added functionality can be expressed as a
59function call, an intrinsic function is the method of choice for LLVM
60extension.</p>
61
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]62<p>Before you invest a significant amount of effort into a non-trivial
63extension, <span class="doc_warning">ask on the list</span> if what you are
64looking to do can be done with already-existing infrastructure, or if maybe
65someone else is already working on it. You will save yourself a lot of time and
66effort by doing so.</p>
67
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]68</div>
69
70<!-- *********************************************************************** -->
71<div class="doc_section">
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]72 <a name="intrinsic">Adding a new intrinsic function</a>
73</div>
74<!-- *********************************************************************** -->
75
76<div class="doc_text">
77
78<p>Adding a new intrinsic function to LLVM is much easier than adding a new
79instruction. Almost all extensions to LLVM should start as an intrinsic
80function and then be turned into an instruction if warranted.</p>
81
82<ol>
83<li><tt>llvm/docs/LangRef.html</tt>:
84 Document the intrinsic. Decide whether it is code generator specific and
85 what the restrictions are. Talk to other people about it so that you are
86 sure it's a good idea.</li>
87
Chris Lattnerc92dba22006-03-09 22:07:39 +0000[diff] [blame^]88<li><tt>llvm/include/llvm/Intrinsics.td</tt>:
89 Add an entry for your intrinsic.</li>
Chris Lattner0190fdb2004-04-10 06:56:53 +0000[diff] [blame]90
91<li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does
Chris Lattner81519d92004-06-20 07:53:22 +0000[diff] [blame]92 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]93 of functions.</li>
94
Nate Begeman2f86c222006-01-14 01:27:10 +0000[diff] [blame]95<li><tt>llvm/lib/Analysis/ConstantFolding.cpp</tt>: If it is possible to
96 constant fold your intrinsic, add support to it in the
97 <tt>canConstantFoldCallTo</tt> and <tt>ConstantFoldCall</tt> functions.</li>
98
99<li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If your intrinsic has no side-
100 effects, add it to the list of intrinsics in the
101 <tt>isInstructionTriviallyDead</tt> function.</li>
Chris Lattnerd828bc62004-04-13 19:48:55 +0000[diff] [blame]102
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]103<li><tt>llvm/test/Regression/*</tt>: Add test cases for your test cases to the
104 test suite</li>
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]105</ol>
106
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]107<p>Once the intrinsic has been added to the system, you must add code generator
108support for it. Generally you must do the following steps:</p>
109
110<dl>
111<dt>Add support to the C backend in <tt>lib/Target/CBackend/</tt></dt>
112
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]113<dd>Depending on the intrinsic, there are a few ways to implement this. For
114most intrinsics, it makes sense to add code to lower your intrinsic in
115<tt>LowerIntrinsicCall</tt> in <tt>lib/CodeGen/IntrinsicLowering.cpp</tt>.
116Second, if it makes sense to lower the intrinsic to an expanded sequence of C
117code in all cases, just emit the expansion in <tt>visitCallInst</tt> in
118<tt>Writer.cpp</tt>. If the intrinsic has some way to express it with GCC
119(or any other compiler) extensions, it can be conditionally supported based on
Chris Lattnerb5f6e252006-01-16 16:31:40 +0000[diff] [blame]120the compiler compiling the CBE output (see <tt>llvm.prefetch</tt> for an
121example).
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]122Third, if the intrinsic really has no way to be lowered, just have the code
123generator emit code that prints an error message and calls abort if executed.
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]124</dd>
125
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]126<dl>
127<dt>Add support to the SelectionDAG Instruction Selector in
128<tt>lib/CodeGen/SelectionDAG/</tt></dt>
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]129
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]130<dd>Since most targets in LLVM use the SelectionDAG framework for generating
131code, you will likely need to add support for your intrinsic there as well.
132This is usually accomplished by adding a new node, and then teaching the
133SelectionDAG code how to handle that node. To do this, follow the steps in
Chris Lattnerb5f6e252006-01-16 16:31:40 +0000[diff] [blame]134the <a href="#sdnode">Adding a new SelectionDAG node</a> section.</dd>
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]135
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]136<dl>
137<dt>Once you have added the new node, add code to
138<tt>SelectionDAG/SelectionDAGISel.cpp</tt> to recognize the intrinsic. In most
139cases, the intrinsic will just be turned into the node you just added. For an
Chris Lattnerb5f6e252006-01-16 16:31:40 +0000[diff] [blame]140example of this, see how <tt>visitIntrinsicCall</tt> handles
141<tt>Intrinsic::ctpop_*</tt>.
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]142</dt>
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]143
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]144</div>
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]145
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]146<!-- *********************************************************************** -->
147<div class="doc_section">
148 <a name="sdnode">Adding a new SelectionDAG node</a>
149</div>
150<!-- *********************************************************************** -->
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]151
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]152<div class="doc_text">
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]153
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]154<p>As with intrinsics, adding a new SelectionDAG node to LLVM is much easier
155than adding a new instruction. New nodes are often added to help represent
156instructions common to many targets. These nodes often map to an LLVM
157instruction (add, sub) or intrinsic (byteswap, population count). In other
158cases, new nodes have been added to allow many targets to perform a common task
159(converting between floating point and integer representation) or capture more
160complicated behavior in a single node (rotate).</p>
Chris Lattner5eb9f0d2005-05-11 03:53:53 +0000[diff] [blame]161
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]162<ol>
163<li><tt>include/llvm/CodeGen/SelectionDAGNodes.h</tt>:
164 Add an enum value for the new SelectionDAG node.</li>
165<li><tt>lib/CodeGen/SelectionDAG/SelectionDAG.cpp</tt>:
166 Add code to print the node to <tt>getOperationName</tt>. If your new node
167 can be evaluated at compile time when given constant arguments (such as an
168 add of a constant with another constant), find the <tt>getNode</tt> method
169 that takes the appropriate number of arguments, and add a case for your node
170 to the switch statement that performs constant folding for nodes that take
171 the same number of arguments as your new node.</li>
172<li><tt>lib/CodeGen/SelectionDAG/LegalizeDAG.cpp</tt>:
173 Add code to <a href="CodeGenerator.html#selectiondag_legalize">legalize,
174 promote, and expand</a> the node as necessary. At a minimum, you will need
175 to add a case statement for your node in <tt>LegalizeOp</tt> which calls
176 LegalizeOp on the node's operands, and returns a new node if any of the
177 operands changed as a result of being legalized. It is likely that not all
178 targets supported by the SelectionDAG framework will natively support the
179 new node. In this case, you must also add code in your node's case
180 statement in <tt>LegalizeOp</tt> to Expand your node into simpler, legal
Chris Lattnerb5f6e252006-01-16 16:31:40 +0000[diff] [blame]181 operations. The case for <tt>ISD::UREM</tt> for expanding a remainder into
182 a divide, multiply, and a subtract is a good example.</li>
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]183<li><tt>lib/CodeGen/SelectionDAG/LegalizeDAG.cpp</tt>:
184 If targets may support the new node being added only at certain sizes, you
185 will also need to add code to your node's case statement in
186 <tt>LegalizeOp</tt> to Promote your node's operands to a larger size, and
187 perform the correct operation. You will also need to add code to
Chris Lattnerb5f6e252006-01-16 16:31:40 +0000[diff] [blame]188 <tt>PromoteOp</tt> to do this as well. For a good example, see
189 <tt>ISD::BSWAP</tt>,
Nate Begeman099d76c2006-01-16 07:54:23 +0000[diff] [blame]190 which promotes its operand to a wider size, performs the byteswap, and then
191 shifts the correct bytes right to emulate the narrower byteswap in the
192 wider type.</li>
193<li><tt>lib/CodeGen/SelectionDAG/LegalizeDAG.cpp</tt>:
194 Add a case for your node in <tt>ExpandOp</tt> to teach the legalizer how to
195 perform the action represented by the new node on a value that has been
196 split into high and low halves. This case will be used to support your
197 node with a 64 bit operand on a 32 bit target.</li>
198<li><tt>lib/CodeGen/SelectionDAG/DAGCombiner.cpp</tt>:
199 If your node can be combined with itself, or other existing nodes in a
200 peephole-like fashion, add a visit function for it, and call that function
201 from <tt></tt>. There are several good examples for simple combines you
202 can do; <tt>visitFABS</tt> and <tt>visitSRL</tt> are good starting places.
203 </li>
204<li><tt>lib/Target/PowerPC/PPCISelLowering.cpp</tt>:
205 Each target has an implementation of the <tt>TargetLowering</tt> class,
206 usually in its own file (although some targets include it in the same
207 file as the DAGToDAGISel). The default behavior for a target is to
208 assume that your new node is legal for all types that are legal for
209 that target. If this target does not natively support your node, then
210 tell the target to either Promote it (if it is supported at a larger
211 type) or Expand it. This will cause the code you wrote in
212 <tt>LegalizeOp</tt> above to decompose your new node into other legal
213 nodes for this target.</li>
214<li><tt>lib/Target/TargetSelectionDAG.td</tt>:
215 Most current targets supported by LLVM generate code using the DAGToDAG
216 method, where SelectionDAG nodes are pattern matched to target-specific
217 nodes, which represent individual instructions. In order for the targets
218 to match an instruction to your new node, you must add a def for that node
219 to the list in this file, with the appropriate type constraints. Look at
220 <tt>add</tt>, <tt>bswap</tt>, and <tt>fadd</tt> for examples.</li>
221<li><tt>lib/Target/PowerPC/PPCInstrInfo.td</tt>:
222 Each target has a tablegen file that describes the target's instruction
223 set. For targets that use the DAGToDAG instruction selection framework,
224 add a pattern for your new node that uses one or more target nodes.
225 Documentation for this is a bit sparse right now, but there are several
226 decent examples. See the patterns for <tt>rotl</tt> in
227 <tt>PPCInstrInfo.td</tt>.</li>
228<li>TODO: document complex patterns.</li>
229<li><tt>llvm/test/Regression/CodeGen/*</tt>: Add test cases for your new node
230 to the test suite. <tt>llvm/test/Regression/CodeGen/X86/bswap.ll</tt> is
231 a good example.</li>
232</ol>
Chris Lattner36365402004-04-09 19:24:20 +0000[diff] [blame]233
234</div>
235
236<!-- *********************************************************************** -->
237<div class="doc_section">
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]238 <a name="instruction">Adding a new instruction</a>
239</div>
240<!-- *********************************************************************** -->
241
242<div class="doc_text">
243
244<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]245format, and it will take some effort to maintain compatibility with
246the previous version.</span> Only add an instruction if it is absolutely
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]247necessary.</p>
248
249<ol>
Misha Brukmanb3b28272004-04-06 04:17:51 +0000[diff] [blame]250
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]251<li><tt>llvm/include/llvm/Instruction.def</tt>:
252 add a number for your instruction and an enum name</li>
253
Misha Brukman47b14a42004-07-29 17:30:56 +0000[diff] [blame]254<li><tt>llvm/include/llvm/Instructions.h</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]255 add a definition for the class that will represent your instruction</li>
256
257<li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
258 add a prototype for a visitor to your new instruction type</li>
259
260<li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
261 add a new token to parse your instruction from assembly text file</li>
262
263<li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>:
264 add the grammar on how your instruction can be read and what it will
265 construct as a result</li>
266
Misha Brukmane39cd632004-09-28 16:58:12 +0000[diff] [blame]267<li><tt>llvm/lib/Bytecode/Reader/Reader.cpp</tt>:
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]268 add a case for your instruction and how it will be parsed from bytecode</li>
269
270<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
271 add a case for how your instruction will be printed out to assembly</li>
272
Chris Lattner8f363212004-07-29 17:31:57 +0000[diff] [blame]273<li><tt>llvm/lib/VMCore/Instructions.cpp</tt>:
Misha Brukmane39cd632004-09-28 16:58:12 +0000[diff] [blame]274 implement the class you defined in
275 <tt>llvm/include/llvm/Instructions.h</tt></li>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]276
Misha Brukmana4242282004-12-01 20:58:54 +0000[diff] [blame]277<li>Test your instruction</li>
278
279<li><tt>llvm/lib/Target/*</tt>:
280 Add support for your instruction to code generators, or add a lowering
281 pass.</li>
282
283<li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
284
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]285</ol>
286
287<p>Also, you need to implement (or modify) any analyses or passes that you want
288to understand this new instruction.</p>
289
290</div>
291
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]292
293<!-- *********************************************************************** -->
294<div class="doc_section">
295 <a name="type">Adding a new type</a>
296</div>
297<!-- *********************************************************************** -->
298
299<div class="doc_text">
300
301<p><span class="doc_warning">WARNING: adding new types changes the bytecode
302format, and will break compatibility with currently-existing LLVM
303installations.</span> Only add new types if it is absolutely necessary.</p>
304
305</div>
306
307<!-- ======================================================================= -->
308<div class="doc_subsection">
309 <a name="fund_type">Adding a fundamental type</a>
310</div>
311
312<div class="doc_text">
313
314<ol>
315
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]316<li><tt>llvm/include/llvm/Type.h</tt>:
Chris Lattner55f95012005-04-23 21:59:11 +0000[diff] [blame]317 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]318
319<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
320 add mapping from <tt>TypeID</tt> =&gt; <tt>Type*</tt>;
321 initialize the static <tt>Type*</tt></li>
322
323<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
324 add ability to parse in the type from text assembly</li>
325
326<li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
327 add a token for that type</li>
328
329</ol>
330
331</div>
332
333<!-- ======================================================================= -->
334<div class="doc_subsection">
335 <a name="derived_type">Adding a derived type</a>
336</div>
337
338<div class="doc_text">
339
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]340<ol>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]341<li><tt>llvm/include/llvm/Type.h</tt>:
Chris Lattner55f95012005-04-23 21:59:11 +0000[diff] [blame]342 add enum for the new type; add a forward declaration of the type
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]343 also</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]344
Chris Lattner47746aa2005-11-13 02:09:55 +0000[diff] [blame]345<li><tt>llvm/include/llvm/DerivedTypes.h</tt>:
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]346 add new class to represent new class in the hierarchy; add forward
347 declaration to the TypeMap value type</li>
348
349<li><tt>llvm/lib/VMCore/Type.cpp</tt>:
350 add support for derived type to:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]351<div class="doc_code">
352<pre>
353std::string getTypeDescription(const Type &amp;Ty,
354 std::vector&lt;const Type*&gt; &amp;TypeStack)
355bool TypesEqual(const Type *Ty, const Type *Ty2,
356 std::map&lt;const Type*, const Type*&gt; &amp; EqTypes)
357</pre>
358</div>
359 add necessary member functions for type, and factory methods</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]360
361<li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
362 add ability to parse in the type from text assembly</li>
363
364<li><tt>llvm/lib/ByteCode/Writer/Writer.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]365 modify <tt>void BytecodeWriter::outputType(const Type *T)</tt> to serialize
366 your type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]367
368<li><tt>llvm/lib/ByteCode/Reader/Reader.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]369 modify <tt>const Type *BytecodeReader::ParseType()</tt> to read your data
370 type</li>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]371
372<li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>:
Misha Brukman7cc8a892004-08-12 19:58:43 +0000[diff] [blame]373 modify
374<div class="doc_code">
375<pre>
376void calcTypeName(const Type *Ty,
377 std::vector&lt;const Type*&gt; &amp;TypeStack,
378 std::map&lt;const Type*,std::string&gt; &amp;TypeNames,
379 std::string &amp; Result)
380</pre>
381</div>
Chris Lattner8dad40c2004-08-12 19:06:24 +0000[diff] [blame]382 to output the new derived type
383</li>
384
385
386</ol>
Misha Brukmana3ce4292004-04-06 03:53:49 +0000[diff] [blame]387
388</div>
389
390<!-- *********************************************************************** -->
391
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