mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-12-21 11:10:12 +00:00
392 lines
16 KiB
HTML
392 lines
16 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
|
|
"http://www.w3.org/TR/html4/strict.dtd">
|
|
<html>
|
|
<head>
|
|
<title>Extending LLVM: Adding instructions, intrinsics, types, etc.</title>
|
|
<link rel="stylesheet" href="llvm.css" type="text/css">
|
|
</head>
|
|
|
|
<body>
|
|
|
|
<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="#sdnode">Adding a new SelectionDAG node</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>,
|
|
Brad Jones, Nate Begeman,
|
|
and <a href="http://nondot.org/sabre">Chris Lattner</a></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 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>
|
|
|
|
<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*.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). 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
|
|
<tt>canConstantFoldCallTo</tt> and <tt>ConstantFoldCall</tt> functions.</li>
|
|
|
|
<li><tt>llvm/test/Regression/*</tt>: Add test cases for your test cases to the
|
|
test suite</li>
|
|
</ol>
|
|
|
|
<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. 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>
|
|
|
|
<dt>Add support to the .td file for the target(s) of your choice in
|
|
<tt>lib/Target/*/*.td</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>
|
|
</dl>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="sdnode">Adding a new SelectionDAG node</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<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
|
|
instructions common to many targets. These nodes often map to an LLVM
|
|
instruction (add, sub) or intrinsic (byteswap, population count). In other
|
|
cases, new nodes have been added to allow many targets to perform a common task
|
|
(converting between floating point and integer representation) or capture more
|
|
complicated behavior in a single node (rotate).</p>
|
|
|
|
<ol>
|
|
<li><tt>include/llvm/CodeGen/SelectionDAGNodes.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
|
|
can be evaluated at compile time when given constant arguments (such as an
|
|
add of a constant with another constant), find the <tt>getNode</tt> method
|
|
that takes the appropriate number of arguments, and add a case for your node
|
|
to the switch statement that performs constant folding for nodes that take
|
|
the same number of arguments as your new node.</li>
|
|
<li><tt>lib/CodeGen/SelectionDAG/LegalizeDAG.cpp</tt>:
|
|
Add code to <a href="CodeGenerator.html#selectiondag_legalize">legalize,
|
|
promote, and expand</a> the node as necessary. At a minimum, you will need
|
|
to add a case statement for your node in <tt>LegalizeOp</tt> which calls
|
|
LegalizeOp on the node's operands, and returns a new node if any of the
|
|
operands changed as a result of being legalized. It is likely that not all
|
|
targets supported by the SelectionDAG framework will natively support the
|
|
new node. In this case, you must also add code in your node's case
|
|
statement in <tt>LegalizeOp</tt> to Expand your node into simpler, legal
|
|
operations. The case for <tt>ISD::UREM</tt> for expanding a remainder into
|
|
a divide, multiply, and a subtract is a good example.</li>
|
|
<li><tt>lib/CodeGen/SelectionDAG/LegalizeDAG.cpp</tt>:
|
|
If targets may support the new node being added only at certain sizes, you
|
|
will also need to add code to your node's case statement in
|
|
<tt>LegalizeOp</tt> to Promote your node's operands to a larger size, and
|
|
perform the correct operation. You will also need to add code to
|
|
<tt>PromoteOp</tt> to do this as well. For a good example, see
|
|
<tt>ISD::BSWAP</tt>,
|
|
which promotes its operand to a wider size, performs the byteswap, and then
|
|
shifts the correct bytes right to emulate the narrower byteswap in the
|
|
wider type.</li>
|
|
<li><tt>lib/CodeGen/SelectionDAG/LegalizeDAG.cpp</tt>:
|
|
Add a case for your node in <tt>ExpandOp</tt> to teach the legalizer how to
|
|
perform the action represented by the new node on a value that has been
|
|
split into high and low halves. This case will be used to support your
|
|
node with a 64 bit operand on a 32 bit target.</li>
|
|
<li><tt>lib/CodeGen/SelectionDAG/DAGCombiner.cpp</tt>:
|
|
If your node can be combined with itself, or other existing nodes in a
|
|
peephole-like fashion, add a visit function for it, and call that function
|
|
from <tt></tt>. There are several good examples for simple combines you
|
|
can do; <tt>visitFABS</tt> and <tt>visitSRL</tt> are good starting places.
|
|
</li>
|
|
<li><tt>lib/Target/PowerPC/PPCISelLowering.cpp</tt>:
|
|
Each target has an implementation of the <tt>TargetLowering</tt> class,
|
|
usually in its own file (although some targets include it in the same
|
|
file as the DAGToDAGISel). The default behavior for a target is to
|
|
assume that your new node is legal for all types that are legal for
|
|
that target. If this target does not natively support your node, then
|
|
tell the target to either Promote it (if it is supported at a larger
|
|
type) or Expand it. This will cause the code you wrote in
|
|
<tt>LegalizeOp</tt> above to decompose your new node into other legal
|
|
nodes for this target.</li>
|
|
<li><tt>lib/Target/TargetSelectionDAG.td</tt>:
|
|
Most current targets supported by LLVM generate code using the DAGToDAG
|
|
method, where SelectionDAG nodes are pattern matched to target-specific
|
|
nodes, which represent individual instructions. In order for the targets
|
|
to match an instruction to your new node, you must add a def for that node
|
|
to the list in this file, with the appropriate type constraints. Look at
|
|
<tt>add</tt>, <tt>bswap</tt>, and <tt>fadd</tt> for examples.</li>
|
|
<li><tt>lib/Target/PowerPC/PPCInstrInfo.td</tt>:
|
|
Each target has a tablegen file that describes the target's instruction
|
|
set. For targets that use the DAGToDAG instruction selection framework,
|
|
add a pattern for your new node that uses one or more target nodes.
|
|
Documentation for this is a bit sparse right now, but there are several
|
|
decent examples. See the patterns for <tt>rotl</tt> in
|
|
<tt>PPCInstrInfo.td</tt>.</li>
|
|
<li>TODO: document complex patterns.</li>
|
|
<li><tt>llvm/test/Regression/CodeGen/*</tt>: Add test cases for your new node
|
|
to the test suite. <tt>llvm/test/Regression/CodeGen/X86/bswap.ll</tt> is
|
|
a good example.</li>
|
|
</ol>
|
|
|
|
</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 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>
|
|
|
|
<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/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>
|
|
|
|
<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 bitcode
|
|
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/DerivedTypes.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/BitCode/Writer/Writer.cpp</tt>:
|
|
modify <tt>void BitcodeWriter::outputType(const Type *T)</tt> to serialize
|
|
your type</li>
|
|
|
|
<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>:
|
|
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>
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
<hr>
|
|
<address>
|
|
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
|
|
src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
|
|
<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://llvm.org">The LLVM Compiler Infrastructure</a>
|
|
<br>
|
|
Last modified: $Date$
|
|
</address>
|
|
|
|
</body>
|
|
</html>
|