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| <title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title> |
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| <div class="doc_title"> |
| Extending LLVM: Adding instructions, intrinsics, types, etc. |
| </div> |
| |
| <ol> |
| <li><a href="#introduction">Introduction and Warning</a></li> |
| <li><a href="#intrinsic">Adding a new intrinsic function</a></li> |
| <li><a href="#instruction">Adding a new instruction</a></li> |
| <li><a href="#type">Adding a new type</a> |
| <ol> |
| <li><a href="#fund_type">Adding a new fundamental type</a></li> |
| <li><a href="#derived_type">Adding a new derived type</a></li> |
| </ol></li> |
| </ol> |
| |
| <div class="doc_author"> |
| <p>Written by <a href="http://misha.brukman.net">Misha Brukman</a> and |
| Brad Jones</p> |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <div class="doc_section"> |
| <a name="introduction">Introduction and Warning</a> |
| </div> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>During the course of using LLVM, you may wish to customize it for your |
| research project or for experimentation. At this point, you may realize that |
| you need to add something to LLVM, whether it be a new fundamental type, a new |
| intrinsic function, or a whole new instruction.</p> |
| |
| <p>When you come to this realization, stop and think. Do you really need to |
| extend LLVM? Is it a new fundamental capability that LLVM does not support at |
| its current incarnation or can it be synthesized from already pre-existing LLVM |
| elements? If you are not sure, ask on the <a |
| href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM-dev</a> list. The |
| reason is that extending LLVM will get involved as you need to update all the |
| different passes that you intend to use with your extension, and there are |
| <em>many</em> LLVM analyses and transformations, so it may be quite a bit of |
| work.</p> |
| |
| <p>Adding an <a href="#intrinsic">intrinsic function</a> is easier than adding |
| an instruction, and is transparent to optimization passes which treat it as an |
| unanalyzable function. If your added functionality can be expressed as a |
| function call, an intrinsic function is the method of choice for LLVM |
| extension.</p> |
| |
| <p>Before you invest a significant amount of effort into a non-trivial |
| extension, <span class="doc_warning">ask on the list</span> if what you are |
| looking to do can be done with already-existing infrastructure, or if maybe |
| someone else is already working on it. You will save yourself a lot of time and |
| effort by doing so.</p> |
| |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <div class="doc_section"> |
| <a name="intrinsic">Adding a new intrinsic function</a> |
| </div> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>Adding a new intrinsic function to LLVM is much easier than adding a new |
| instruction. Almost all extensions to LLVM should start as an intrinsic |
| function and then be turned into an instruction if warranted.</p> |
| |
| <ol> |
| <li><tt>llvm/docs/LangRef.html</tt>: |
| Document the intrinsic. Decide whether it is code generator specific and |
| what the restrictions are. Talk to other people about it so that you are |
| sure it's a good idea.</li> |
| |
| <li><tt>llvm/include/llvm/Intrinsics.h</tt>: |
| add an enum in the <tt>llvm::Intrinsic</tt> namespace</li> |
| |
| <li><tt>llvm/lib/CodeGen/IntrinsicLowering.cpp</tt>: |
| implement the lowering for this intrinsic</li> |
| |
| <li><tt>llvm/lib/VMCore/Verifier.cpp</tt>: |
| Add code to check the invariants of the intrinsic are respected.</li> |
| |
| <li><tt>llvm/lib/VMCore/Function.cpp (<tt>Function::getIntrinsicID()</tt>)</tt>: |
| Identify the new intrinsic function, returning the enum for the intrinsic |
| that you added.</li> |
| |
| <li><tt>llvm/lib/Analysis/BasicAliasAnalysis.cpp</tt>: If the new intrinsic does |
| not access memory or does not write to memory, add it to the relevant list |
| of functions.</li> |
| |
| <li><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to |
| constant-propagate your intrinsic, add support to it in the |
| <tt>canConstantFoldCallTo</tt> and <tt>ConstantFoldCall</tt> functions.</li> |
| |
| <li>Test your intrinsic</li> |
| |
| <li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite</li> |
| </ol> |
| |
| <p>If this intrinsic requires code generator support (i.e., it cannot be |
| lowered), you should also add support to the code generator in question.</p> |
| |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <div class="doc_section"> |
| <a name="instruction">Adding a new instruction</a> |
| </div> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p><span class="doc_warning">WARNING: adding instructions changes the bytecode |
| format, and it will take some effort to maintain compatibility with |
| the previous version.</span> Only add an instruction if it is absolutely |
| necessary.</p> |
| |
| <ol> |
| |
| <li><tt>llvm/include/llvm/Instruction.def</tt>: |
| add a number for your instruction and an enum name</li> |
| |
| <li><tt>llvm/include/llvm/Instructions.h</tt>: |
| add a definition for the class that will represent your instruction</li> |
| |
| <li><tt>llvm/include/llvm/Support/InstVisitor.h</tt>: |
| add a prototype for a visitor to your new instruction type</li> |
| |
| <li><tt>llvm/lib/AsmParser/Lexer.l</tt>: |
| add a new token to parse your instruction from assembly text file</li> |
| |
| <li><tt>llvm/lib/AsmParser/llvmAsmParser.y</tt>: |
| add the grammar on how your instruction can be read and what it will |
| construct as a result</li> |
| |
| <li><tt>llvm/lib/Bytecode/Reader/Reader.cpp</tt>: |
| add a case for your instruction and how it will be parsed from bytecode</li> |
| |
| <li><tt>llvm/lib/VMCore/Instruction.cpp</tt>: |
| add a case for how your instruction will be printed out to assembly</li> |
| |
| <li><tt>llvm/lib/VMCore/Instructions.cpp</tt>: |
| implement the class you defined in |
| <tt>llvm/include/llvm/Instructions.h</tt></li> |
| |
| <li>Test your instruction</li> |
| |
| <li><tt>llvm/lib/Target/*</tt>: |
| Add support for your instruction to code generators, or add a lowering |
| pass.</li> |
| |
| <li><tt>llvm/test/Regression/*</tt>: add your test cases to the test suite.</li> |
| |
| </ol> |
| |
| <p>Also, you need to implement (or modify) any analyses or passes that you want |
| to understand this new instruction.</p> |
| |
| </div> |
| |
| |
| <!-- *********************************************************************** --> |
| <div class="doc_section"> |
| <a name="type">Adding a new type</a> |
| </div> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p><span class="doc_warning">WARNING: adding new types changes the bytecode |
| format, and will break compatibility with currently-existing LLVM |
| installations.</span> Only add new types if it is absolutely necessary.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="fund_type">Adding a fundamental type</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <ol> |
| |
| <li><tt>llvm/include/llvm/Type.h</tt>: |
| add enum for the new type; add static <tt>Type*</tt> for this type</li> |
| |
| <li><tt>llvm/lib/VMCore/Type.cpp</tt>: |
| add mapping from <tt>TypeID</tt> => <tt>Type*</tt>; |
| initialize the static <tt>Type*</tt></li> |
| |
| <li><tt>llvm/lib/AsmReader/Lexer.l</tt>: |
| add ability to parse in the type from text assembly</li> |
| |
| <li><tt>llvm/lib/AsmReader/llvmAsmParser.y</tt>: |
| add a token for that type</li> |
| |
| </ol> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <div class="doc_subsection"> |
| <a name="derived_type">Adding a derived type</a> |
| </div> |
| |
| <div class="doc_text"> |
| |
| <ol> |
| <li><tt>llvm/include/llvm/Type.h</tt>: |
| add enum for the new type; add a forward declaration of the type |
| also</li> |
| |
| <li><tt>llvm/include/llvm/DerivedType.h</tt>: |
| add new class to represent new class in the hierarchy; add forward |
| declaration to the TypeMap value type</li> |
| |
| <li><tt>llvm/lib/VMCore/Type.cpp</tt>: |
| add support for derived type to: |
| <div class="doc_code"> |
| <pre> |
| std::string getTypeDescription(const Type &Ty, |
| std::vector<const Type*> &TypeStack) |
| bool TypesEqual(const Type *Ty, const Type *Ty2, |
| std::map<const Type*, const Type*> & EqTypes) |
| </pre> |
| </div> |
| add necessary member functions for type, and factory methods</li> |
| |
| <li><tt>llvm/lib/AsmReader/Lexer.l</tt>: |
| add ability to parse in the type from text assembly</li> |
| |
| <li><tt>llvm/lib/ByteCode/Writer/Writer.cpp</tt>: |
| modify <tt>void BytecodeWriter::outputType(const Type *T)</tt> to serialize |
| your type</li> |
| |
| <li><tt>llvm/lib/ByteCode/Reader/Reader.cpp</tt>: |
| modify <tt>const Type *BytecodeReader::ParseType()</tt> to read your data |
| type</li> |
| |
| <li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>: |
| modify |
| <div class="doc_code"> |
| <pre> |
| void calcTypeName(const Type *Ty, |
| std::vector<const Type*> &TypeStack, |
| std::map<const Type*,std::string> &TypeNames, |
| std::string & Result) |
| </pre> |
| </div> |
| to output the new derived type |
| </li> |
| |
| |
| </ol> |
| |
| </div> |
| |
| <!-- *********************************************************************** --> |
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| <a href="http://misha.brukman.net">Misha Brukman</a><br> |
| <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a> |
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| Last modified: $Date$ |
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