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<title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
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+<h1>
Extending LLVM: Adding instructions, intrinsics, types, etc.
-</div>
+</h1>
<ol>
<li><a href="#introduction">Introduction and Warning</a></li>
</div>
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-<div class="doc_section">
+<h2>
<a name="introduction">Introduction and Warning</a>
-</div>
+</h2>
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-<div class="doc_text">
+<div>
<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
</div>
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-<div class="doc_section">
+<h2>
<a name="intrinsic">Adding a new intrinsic function</a>
-</div>
+</h2>
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-<div class="doc_text">
+<div>
<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
<li><tt>llvm/include/llvm/Intrinsics*.td</tt>:
Add an entry for your intrinsic. Describe its memory access characteristics
- for optimization (this controls whether it will be DCE'd, CSE'd, etc).</li>
+ for optimization (this controls whether it will be DCE'd, CSE'd, etc). Note
+ that any intrinsic using the <tt>llvm_int_ty</tt> type for an argument will
+ be deemed by <tt>tblgen</tt> as overloaded and the corresponding suffix
+ will be required on the intrinsic's name.</li>
<li><tt>llvm/lib/Analysis/ConstantFolding.cpp</tt>: If it is possible to
constant fold your intrinsic, add support to it in the
support for it. Generally you must do the following steps:</p>
<dl>
-<dt>Add support to the C backend in <tt>lib/Target/CBackend/</tt></dt>
-
-<dd>Depending on the intrinsic, there are a few ways to implement this. For
-most intrinsics, it makes sense to add code to lower your intrinsic in
-<tt>LowerIntrinsicCall</tt> in <tt>lib/CodeGen/IntrinsicLowering.cpp</tt>.
-Second, if it makes sense to lower the intrinsic to an expanded sequence of C
-code in all cases, just emit the expansion in <tt>visitCallInst</tt> in
-<tt>Writer.cpp</tt>. If the intrinsic has some way to express it with GCC
-(or any other compiler) extensions, it can be conditionally supported based on
-the compiler compiling the CBE output (see <tt>llvm.prefetch</tt> for an
-example).
-Third, if the intrinsic really has no way to be lowered, just have the code
-generator emit code that prints an error message and calls abort if executed.
-</dd>
-<dl>
<dt>Add support to the .td file for the target(s) of your choice in
<tt>lib/Target/*/*.td</tt>.</dt>
the intrinsic, though it may obviously require adding the instructions you
want to generate as well. There are lots of examples in the PowerPC and X86
backend to follow.</dd>
+</dl>
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-<div class="doc_section">
+<h2>
<a name="sdnode">Adding a new SelectionDAG node</a>
-</div>
+</h2>
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-<div class="doc_text">
+<div>
<p>As with intrinsics, adding a new SelectionDAG node to LLVM is much easier
than adding a new instruction. New nodes are often added to help represent
complicated behavior in a single node (rotate).</p>
<ol>
-<li><tt>include/llvm/CodeGen/SelectionDAGNodes.h</tt>:
+<li><tt>include/llvm/CodeGen/ISDOpcodes.h</tt>:
Add an enum value for the new SelectionDAG node.</li>
<li><tt>lib/CodeGen/SelectionDAG/SelectionDAG.cpp</tt>:
Add code to print the node to <tt>getOperationName</tt>. If your new node
</div>
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-<div class="doc_section">
+<h2>
<a name="instruction">Adding a new instruction</a>
-</div>
+</h2>
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-<div class="doc_text">
+<div>
-<p><span class="doc_warning">WARNING: adding instructions changes the bytecode
+<p><span class="doc_warning">WARNING: adding instructions changes the bitcode
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>
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/Bitcode/Reader/Reader.cpp</tt>:
+ add a case for your instruction and how it will be parsed from bitcode</li>
<li><tt>llvm/lib/VMCore/Instruction.cpp</tt>:
add a case for how your instruction will be printed out to assembly</li>
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-<div class="doc_section">
+<h2>
<a name="type">Adding a new type</a>
-</div>
+</h2>
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-<div class="doc_text">
+<div>
-<p><span class="doc_warning">WARNING: adding new types changes the bytecode
+<p><span class="doc_warning">WARNING: adding new types changes the bitcode
format, and will break compatibility with currently-existing LLVM
installations.</span> Only add new types if it is absolutely necessary.</p>
-</div>
-
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-<div class="doc_subsection">
+<h3>
<a name="fund_type">Adding a fundamental type</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<ol>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="derived_type">Adding a derived type</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<ol>
<li><tt>llvm/include/llvm/Type.h</tt>:
<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
+<li><tt>llvm/lib/BitCode/Writer/Writer.cpp</tt>:
+ modify <tt>void BitcodeWriter::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
+<li><tt>llvm/lib/BitCode/Reader/Reader.cpp</tt>:
+ modify <tt>const Type *BitcodeReader::ParseType()</tt> to read your data
type</li>
<li><tt>llvm/lib/VMCore/AsmWriter.cpp</tt>:
</div>
+</div>
+
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