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Update adding an intrinsic to describe that you can now just plop it into the

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target .td file instead of adding SDNodes etc.

llvm-svn: 27616
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Chris Lattner 2006-04-12 17:42:39 +00:00
parent d35df8adf9
commit 70404dc8b5
1 changed files with 12 additions and 20 deletions
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@ -53,9 +53,9 @@ 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
<p>Adding an <a href="#intrinsic">intrinsic function</a> is far easier than
adding an instruction, and is transparent to optimization passes. If your added
functionality can be expressed as a
function call, an intrinsic function is the method of choice for LLVM
extension.</p>
@ -85,8 +85,9 @@ function and then be turned into an instruction if warranted.</p>
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.td</tt>:
Add an entry for your intrinsic.</li>
<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>
<li><tt>llvm/lib/Analysis/ConstantFolding.cpp</tt>: If it is possible to
constant fold your intrinsic, add support to it in the
@ -116,22 +117,13 @@ generator emit code that prints an error message and calls abort if executed.
</dd>
<dl>
<dt>Add support to the SelectionDAG Instruction Selector in
<tt>lib/CodeGen/SelectionDAG/</tt></dt>
<dt>Add support to the .td file for the target(s) of your choice in
<tt>lib/Target/*/*.td</tt>.</dt>
<dd>Since most targets in LLVM use the SelectionDAG framework for generating
code, you will likely need to add support for your intrinsic there as well.
This is usually accomplished by adding a new node, and then teaching the
SelectionDAG code how to handle that node. To do this, follow the steps in
the <a href="#sdnode">Adding a new SelectionDAG node</a> section.</dd>
<dl>
<dt>Once you have added the new node, add code to
<tt>SelectionDAG/SelectionDAGISel.cpp</tt> to recognize the intrinsic. In most
cases, the intrinsic will just be turned into the node you just added. For an
example of this, see how <tt>visitIntrinsicCall</tt> handles
<tt>Intrinsic::ctpop_*</tt>.
</dt>
<dd>This is usually a matter of adding a pattern to the .td file that matches
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>
</div>