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5 <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
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11 <div class="doc_title">
12 Extending LLVM: Adding instructions, intrinsics, types, etc.
16 <li><a href="#introduction">Introduction and Warning</a></li>
17 <li><a href="#intrinsic">Adding a new intrinsic function</a></li>
18 <li><a href="#instruction">Adding a new instruction</a></li>
19 <li><a href="#type">Adding a new type</a>
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>
26 <div class="doc_author">
27 <p>Written by <a href="http://misha.brukman.net">Misha Brukman</a> and
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32 <div class="doc_section">
33 <a name="introduction">Introduction and Warning</a>
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37 <div class="doc_text">
39 <p>During the course of using LLVM, you may wish to customize it for your
40 research project or for experimentation. At this point, you may realize that
41 you need to add something to LLVM, whether it be a new fundamental type, a new
42 intrinsic function, or a whole new instruction.</p>
44 <p>When you come to this realization, stop and think. Do you really need to
45 extend LLVM? Is it a new fundamental capability that LLVM does not support at
46 its current incarnation or can it be synthesized from already pre-existing LLVM
47 elements? If you are not sure, ask on the <a
48 href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a> list. The
49 reason is that extending LLVM will get involved as you need to update all the
50 different 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
54 <p>Adding an <a href="#intrinsic">intrinsic function</a> is easier than adding
55 an instruction, and is transparent to optimization passes which treat it as an
56 unanalyzable function. If your added functionality can be expressed as a
57 function call, an intrinsic function is the method of choice for LLVM
60 <p>Before you invest a significant amount of effort into a non-trivial
61 extension, <span class="doc_warning">ask on the list</span> if what you are
62 looking to do can be done with already-existing infrastructure, or if maybe
63 someone else is already working on it. You will save yourself a lot of time and
64 effort by doing so.</p>
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69 <div class="doc_section">
70 <a name="intrinsic">Adding a new intrinsic function</a>
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74 <div class="doc_text">
76 <p>Adding a new intrinsic function to LLVM is much easier than adding a new
77 instruction. Almost all extensions to LLVM should start as an intrinsic
78 function and then be turned into an instruction if warranted.</p>
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>
86 <li><tt>llvm/include/llvm/Intrinsics.h</tt>:
87 add an enum in the <tt>llvm::Intrinsic</tt> namespace</li>
89 <li><tt>llvm/lib/CodeGen/IntrinsicLowering.cpp</tt>:
90 implement the lowering for this intrinsic</li>
92 <li><tt>llvm/lib/VMCore/Verifier.cpp</tt>:
93 Add code to check the invariants of the intrinsic are respected.</li>
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
99 <li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does
100 not access memory or does not write to memory, add it to the relevant list
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
105 <tt>canConstantFoldCallTo</tt> and <tt>ConstantFoldCall</tt> functions.</li>
107 <li>Test your intrinsic</li>
109 <li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite</li>
112 <p>If this intrinsic requires code generator support (i.e., it cannot be
113 lowered), you should also add support to the code generator in question.</p>
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118 <div class="doc_section">
119 <a name="instruction">Adding a new instruction</a>
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123 <div class="doc_text">
125 <p><span class="doc_warning">WARNING: adding instructions changes the bytecode
126 format, and it will take some effort to maintain compatibility with
127 the previous version.</span> Only add an instruction if it is absolutely
132 <li><tt>llvm/include/llvm/Instruction.def</tt>:
133 add a number for your instruction and an enum name</li>
135 <li><tt>llvm/include/llvm/Instructions.h</tt>:
136 add a definition for the class that will represent your instruction</li>
138 <li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>:
139 add a prototype for a visitor to your new instruction type</li>
141 <li><tt>llvm/lib/AsmParser/Lexer.l</tt>:
142 add a new token to parse your instruction from assembly text file</li>
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>
148 <li><tt>llvm/lib/Bytecode/Reader/Reader.cpp</tt>:
149 add a case for your instruction and how it will be parsed from bytecode</li>
151 <li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
152 add a case for how your instruction will be printed out to assembly</li>
154 <li><tt>llvm/lib/VMCore/Instructions.cpp</tt>:
155 implement the class you defined in
156 <tt>llvm/include/llvm/Instructions.h</tt></li>
158 <li>Test your instruction</li>
160 <li><tt>llvm/lib/Target/*</tt>:
161 Add support for your instruction to code generators, or add a lowering
164 <li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li>
168 <p>Also, you need to implement (or modify) any analyses or passes that you want
169 to understand this new instruction.</p>
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175 <div class="doc_section">
176 <a name="type">Adding a new type</a>
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180 <div class="doc_text">
182 <p><span class="doc_warning">WARNING: adding new types changes the bytecode
183 format, and will break compatibility with currently-existing LLVM
184 installations.</span> Only add new types if it is absolutely necessary.</p>
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189 <div class="doc_subsection">
190 <a name="fund_type">Adding a fundamental type</a>
193 <div class="doc_text">
197 <li><tt>llvm/include/llvm/Type.def</tt>:
198 add enum for the type</li>
200 <li><tt>llvm/include/llvm/Type.h</tt>:
201 add ID number for the new type; add static <tt>Type*</tt> for this type</li>
203 <li><tt>llvm/lib/VMCore/Type.cpp</tt>:
204 add mapping from <tt>TypeID</tt> => <tt>Type*</tt>;
205 initialize the static <tt>Type*</tt></li>
207 <li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
208 add ability to parse in the type from text assembly</li>
210 <li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>:
211 add a token for that type</li>
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218 <div class="doc_subsection">
219 <a name="derived_type">Adding a derived type</a>
222 <div class="doc_text">
225 <li><tt>llvm/include/llvm/Type.def</tt>:
226 add enum for the type</li>
228 <li><tt>llvm/include/llvm/Type.h</tt>:
229 add ID number for the new type; add a forward declaration of the type
232 <li><tt>llvm/include/llvm/DerivedType.h</tt>:
233 add new class to represent new class in the hierarchy; add forward
234 declaration to the TypeMap value type</li>
236 <li><tt>llvm/lib/VMCore/Type.cpp</tt>:
237 add support for derived type to:
238 <div class="doc_code">
240 std::string getTypeDescription(const Type &Ty,
241 std::vector<const Type*> &TypeStack)
242 bool TypesEqual(const Type *Ty, const Type *Ty2,
243 std::map<const Type*, const Type*> & EqTypes)
246 add necessary member functions for type, and factory methods</li>
248 <li><tt>llvm/lib/AsmReader/Lexer.l</tt>:
249 add ability to parse in the type from text assembly</li>
251 <li><tt>llvm/lib/ByteCode/Writer/Writer.cpp</tt>:
252 modify <tt>void BytecodeWriter::outputType(const Type *T)</tt> to serialize
255 <li><tt>llvm/lib/ByteCode/Reader/Reader.cpp</tt>:
256 modify <tt>const Type *BytecodeReader::ParseType()</tt> to read your data
259 <li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>:
261 <div class="doc_code">
263 void calcTypeName(const Type *Ty,
264 std::vector<const Type*> &TypeStack,
265 std::map<const Type*,std::string> &TypeNames,
266 std::string & Result)
269 to output the new derived type
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286 <a href="http://misha.brukman.net">Misha Brukman</a><br>
287 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
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