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update this to reflect the new selection daggy world

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21853 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2005-05-11 03:53:53 +00:00
parent 590cff389d
commit 5eb9f0d56c
1 changed files with 53 additions and 11 deletions
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docs/ExtendingLLVM.html
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@ -24,8 +24,8 @@
</ol>
<div class="doc_author">
<p>Written by <a href="http://misha.brukman.net">Misha Brukman</a> and
Brad Jones</p>
<p>Written by <a href="http://misha.brukman.net">Misha Brukman</a>,
Brad Jones, and <a href="http://nondot.org/sabre">Chris Lattner</a></p>
</div>
<!-- *********************************************************************** -->
@ -86,9 +86,6 @@ function and then be turned into an instruction if warranted.</p>
<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>
@ -100,17 +97,63 @@ function and then be turned into an instruction if warranted.</p>
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><tt>llvm/lib/Transforms/Utils/Local.cpp</tt>: If it is possible to constant
fold 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>
<p>Once the intrinsic has been added to the system, you must add code generator
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. First,
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>. Second, 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 llvm.prefetch 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>
<dt>Add a enum value for the SelectionDAG node in
<tt>include/llvm/CodeGen/SelectionDAGNodes.h</tt></dt>
<dd>Also, add code to <tt>lib/CodeGen/SelectionDAG/SelectionDAG.cpp</tt> (and
<tt>SelectionDAGPrinter.cpp</tt>) to print the node.</dd>
<dt>Add code to <tt>SelectionDAG/SelectionDAGISel.cpp</tt> to recognize the
intrinsic.</dt>
<dd>Presumably the intrinsic should be recognized and turned into the node you
added above.</dd>
<dt>Add code to <tt>SelectionDAG/LegalizeDAG.cpp</tt> to <a
href="CodeGenerator.html#selectiondag_legalize">legalize, promote, and
expand</a> the node as necessary.</dt>
<dd>If the intrinsic can be expanded to primitive operations, legalize can break
the node down into other elementary operations that are be supported.</dd>
<dt>Add target-specific support to specific code generators.</dt>
<dd>Extend the code generators you are interested in to recognize and support
the node, emitting the code you want.</dd>
</dl>
<p>
Unfortunately, the process of extending the code generator to support a new node
is not extremely well documented. As such, it is often helpful to look at other
intrinsics (e.g. <tt>llvm.ctpop</tt>) to see how they are recognized and turned
into a node by <tt>SelectionDAGISel.cpp</tt>, legalized by
<tt>LegalizeDAG.cpp</tt>, then finally emitted by the various code generators.
</p>
</div>
@ -277,7 +320,6 @@ void calcTypeName(const Type *Ty,
<a href="http://validator.w3.org/check/referer"><img
src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
<a href="http://misha.brukman.net">Misha Brukman</a><br>
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
<br>
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