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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>
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+<h2>
<a name="introduction">Introduction and Warning</a>
-</div>
+</h2>
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+<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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+<h2>
<a name="intrinsic">Adding a new intrinsic function</a>
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+</h2>
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+<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
<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>
+ 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>
</div>
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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 bitcode
format, and it will take some effort to maintain compatibility with
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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 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>
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-<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>:
</div>
+</div>
+
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