X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=docs%2FExtendingLLVM.html;h=647fa01d53bbca054ea108d0e1259f39f93c7d65;hb=1ac022974a75aaccc11d9f7f024044cba7ee99f8;hp=8e2a90409cb85b5652301da207d0d9b73a433acc;hpb=39dccd8130d37e0ace37c4bb3c302a9796509088;p=oota-llvm.git
diff --git a/docs/ExtendingLLVM.html b/docs/ExtendingLLVM.html
index 8e2a90409cb..647fa01d53b 100644
--- a/docs/ExtendingLLVM.html
+++ b/docs/ExtendingLLVM.html
@@ -16,6 +16,7 @@
Adding a new type
- Adding a new fundamental type
@@ -24,8 +25,9 @@
@@ -51,9 +53,9 @@ different passes that you intend to use with your extension, and there are
many LLVM analyses and transformations, so it may be quite a bit of
work.
-Adding an intrinsic function 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
+
Adding an intrinsic function 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.
@@ -83,33 +85,137 @@ function and then be turned into an instruction if warranted.
what the restrictions are. Talk to other people about it so that you are
sure it's a good idea.
-Once the intrinsic has been added to the system, you must add code generator
+support for it. Generally you must do the following steps:
+
+
-
If this intrinsic requires code generator support (ie, it cannot be lowered).
-You should also add support to the code generator in question.
+
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).
+
+
+- include/llvm/CodeGen/SelectionDAGNodes.h:
+ Add an enum value for the new SelectionDAG node.
+- lib/CodeGen/SelectionDAG/SelectionDAG.cpp:
+ Add code to print the node to getOperationName. 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 getNode 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.
+- lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:
+ Add code to legalize,
+ promote, and expand the node as necessary. At a minimum, you will need
+ to add a case statement for your node in LegalizeOp 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 LegalizeOp to Expand your node into simpler, legal
+ operations. The case for ISD::UREM for expanding a remainder into
+ a divide, multiply, and a subtract is a good example.
+- lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:
+ 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
+ LegalizeOp to Promote your node's operands to a larger size, and
+ perform the correct operation. You will also need to add code to
+ PromoteOp to do this as well. For a good example, see
+ ISD::BSWAP,
+ 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.
+- lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:
+ Add a case for your node in ExpandOp 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.
+- lib/CodeGen/SelectionDAG/DAGCombiner.cpp:
+ 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 . There are several good examples for simple combines you
+ can do; visitFABS and visitSRL are good starting places.
+
+- lib/Target/PowerPC/PPCISelLowering.cpp:
+ Each target has an implementation of the TargetLowering 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
+ LegalizeOp above to decompose your new node into other legal
+ nodes for this target.
+- lib/Target/TargetSelectionDAG.td:
+ 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
+ add, bswap, and fadd for examples.
+- lib/Target/PowerPC/PPCInstrInfo.td:
+ 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 rotl in
+ PPCInstrInfo.td.
+- TODO: document complex patterns.
+- llvm/test/Regression/CodeGen/*: Add test cases for your new node
+ to the test suite. llvm/test/Regression/CodeGen/X86/bswap.ll is
+ a good example.
+
@@ -121,7 +227,7 @@ You should also add support to the code generator in question.
-
WARNING: adding instructions changes the bytecode
+WARNING: adding instructions changes the bitcode
format, and it will take some effort to maintain compatibility with
the previous version. Only add an instruction if it is absolutely
necessary.
@@ -144,14 +250,23 @@ necessary.
add the grammar on how your instruction can be read and what it will
construct as a result
-
llvm/lib/Bytecode/Reader/InstructionReader.cpp:
- add a case for your instruction and how it will be parsed from bytecode
+
llvm/lib/Bitcode/Reader/Reader.cpp:
+ add a case for your instruction and how it will be parsed from bitcode
llvm/lib/VMCore/Instruction.cpp:
add a case for how your instruction will be printed out to assembly
llvm/lib/VMCore/Instructions.cpp:
- implement the class you defined in llvm/include/llvm/Instructions.h
+ implement the class you defined in
+
llvm/include/llvm/Instructions.h
+
+
Test your instruction
+
+
llvm/lib/Target/*:
+ Add support for your instruction to code generators, or add a lowering
+ pass.
+
+
llvm/test/Regression/*: add your test cases to the test suite.
@@ -169,7 +284,7 @@ to understand this new instruction.
-
WARNING: adding new types changes the bytecode
+WARNING: adding new types changes the bitcode
format, and will break compatibility with currently-existing LLVM
installations. Only add new types if it is absolutely necessary.
@@ -184,11 +299,8 @@ installations. Only add new types if it is absolutely necessary.
-- llvm/include/llvm/Type.def:
- add enum for the type
-
- llvm/include/llvm/Type.h:
- add ID number for the new type; add static Type* for this type
+ add enum for the new type; add static Type* for this type
- llvm/lib/VMCore/Type.cpp:
add mapping from TypeID => Type*;
@@ -212,14 +324,11 @@ installations. Only add new types if it is absolutely necessary.
-- llvm/include/llvm/Type.def:
- add enum for the type
-
- llvm/include/llvm/Type.h:
- add ID number for the new type; add a forward declaration of the type
+ add enum for the new type; add a forward declaration of the type
also
-- llvm/include/llvm/DerivedType.h:
+
- llvm/include/llvm/DerivedTypes.h:
add new class to represent new class in the hierarchy; add forward
declaration to the TypeMap value type
@@ -238,12 +347,12 @@ bool TypesEqual(const Type *Ty, const Type *Ty2,
- llvm/lib/AsmReader/Lexer.l:
add ability to parse in the type from text assembly
-- llvm/lib/ByteCode/Writer/Writer.cpp:
- modify void BytecodeWriter::outputType(const Type *T) to serialize
+
- llvm/lib/BitCode/Writer/Writer.cpp:
+ modify void BitcodeWriter::outputType(const Type *T) to serialize
your type
-- llvm/lib/ByteCode/Reader/Reader.cpp:
- modify const Type *BytecodeReader::ParseType() to read your data
+
- llvm/lib/BitCode/Reader/Reader.cpp:
+ modify const Type *BitcodeReader::ParseType() to read your data
type
- llvm/lib/VMCore/AsmWriter.cpp:
@@ -269,12 +378,11 @@ void calcTypeName(const Type *Ty,
+ src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS">
+ src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01">
- Misha Brukman
- The LLVM Compiler Infrastructure
+ The LLVM Compiler Infrastructure
Last modified: $Date$