diff options
| author | mike-m <mikem.llvm@gmail.com> | 2010-05-06 23:45:43 +0000 |
|---|---|---|
| committer | mike-m <mikem.llvm@gmail.com> | 2010-05-06 23:45:43 +0000 |
| commit | 68cb31901c590cabceee6e6356d62c84142114cb (patch) | |
| tree | 6444bddc975b662fbe47d63cd98a7b776a407c1a /docs/WritingAnLLVMBackend.html | |
| parent | c26ae5ab7e2d65b67c97524e66f50ce86445dec7 (diff) | |
Overhauled llvm/clang docs builds. Closes PR6613.
NOTE: 2nd part changeset for cfe trunk to follow.
*** PRE-PATCH ISSUES ADDRESSED
- clang api docs fail build from objdir
- clang/llvm api docs collide in install PREFIX/
- clang/llvm main docs collide in install
- clang/llvm main docs have full of hard coded destination
assumptions and make use of absolute root in static html files;
namely CommandGuide tools hard codes a website destination
for cross references and some html cross references assume
website root paths
*** IMPROVEMENTS
- bumped Doxygen from 1.4.x -> 1.6.3
- splits llvm/clang docs into 'main' and 'api' (doxygen) build trees
- provide consistent, reliable doc builds for both main+api docs
- support buid vs. install vs. website intentions
- support objdir builds
- document targets with 'make help'
- correct clean and uninstall operations
- use recursive dir delete only where absolutely necessary
- added call function fn.RMRF which safeguards against botched 'rm -rf';
if any target (or any variable is evaluated) which attempts
to remove any dirs which match a hard-coded 'safelist', a verbose
error will be printed and make will error-stop.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103213 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs/WritingAnLLVMBackend.html')
| -rw-r--r-- | docs/WritingAnLLVMBackend.html | 2561 |
1 files changed, 0 insertions, 2561 deletions
diff --git a/docs/WritingAnLLVMBackend.html b/docs/WritingAnLLVMBackend.html deleted file mode 100644 index f49875c204..0000000000 --- a/docs/WritingAnLLVMBackend.html +++ /dev/null @@ -1,2561 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" - "http://www.w3.org/TR/html4/strict.dtd"> -<html> -<head> - <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> - <title>Writing an LLVM Compiler Backend</title> - <link rel="stylesheet" href="llvm.css" type="text/css"> -</head> - -<body> - -<div class="doc_title"> - Writing an LLVM Compiler Backend -</div> - -<ol> - <li><a href="#intro">Introduction</a> - <ul> - <li><a href="#Audience">Audience</a></li> - <li><a href="#Prerequisite">Prerequisite Reading</a></li> - <li><a href="#Basic">Basic Steps</a></li> - <li><a href="#Preliminaries">Preliminaries</a></li> - </ul> - <li><a href="#TargetMachine">Target Machine</a></li> - <li><a href="#TargetRegistration">Target Registration</a></li> - <li><a href="#RegisterSet">Register Set and Register Classes</a> - <ul> - <li><a href="#RegisterDef">Defining a Register</a></li> - <li><a href="#RegisterClassDef">Defining a Register Class</a></li> - <li><a href="#implementRegister">Implement a subclass of TargetRegisterInfo</a></li> - </ul></li> - <li><a href="#InstructionSet">Instruction Set</a> - <ul> - <li><a href="#operandMapping">Instruction Operand Mapping</a></li> - <li><a href="#implementInstr">Implement a subclass of TargetInstrInfo</a></li> - <li><a href="#branchFolding">Branch Folding and If Conversion</a></li> - </ul></li> - <li><a href="#InstructionSelector">Instruction Selector</a> - <ul> - <li><a href="#LegalizePhase">The SelectionDAG Legalize Phase</a> - <ul> - <li><a href="#promote">Promote</a></li> - <li><a href="#expand">Expand</a></li> - <li><a href="#custom">Custom</a></li> - <li><a href="#legal">Legal</a></li> - </ul></li> - <li><a href="#callingConventions">Calling Conventions</a></li> - </ul></li> - <li><a href="#assemblyPrinter">Assembly Printer</a></li> - <li><a href="#subtargetSupport">Subtarget Support</a></li> - <li><a href="#jitSupport">JIT Support</a> - <ul> - <li><a href="#mce">Machine Code Emitter</a></li> - <li><a href="#targetJITInfo">Target JIT Info</a></li> - </ul></li> -</ol> - -<div class="doc_author"> - <p>Written by <a href="http://www.woo.com">Mason Woo</a> and - <a href="http://misha.brukman.net">Misha Brukman</a></p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="intro">Introduction</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p> -This document describes techniques for writing compiler backends that convert -the LLVM Intermediate Representation (IR) to code for a specified machine or -other languages. Code intended for a specific machine can take the form of -either assembly code or binary code (usable for a JIT compiler). -</p> - -<p> -The backend of LLVM features a target-independent code generator that may create -output for several types of target CPUs — including X86, PowerPC, Alpha, -and SPARC. The backend may also be used to generate code targeted at SPUs of the -Cell processor or GPUs to support the execution of compute kernels. -</p> - -<p> -The document focuses on existing examples found in subdirectories -of <tt>llvm/lib/Target</tt> in a downloaded LLVM release. In particular, this -document focuses on the example of creating a static compiler (one that emits -text assembly) for a SPARC target, because SPARC has fairly standard -characteristics, such as a RISC instruction set and straightforward calling -conventions. -</p> - -</div> - -<div class="doc_subsection"> - <a name="Audience">Audience</a> -</div> - -<div class="doc_text"> - -<p> -The audience for this document is anyone who needs to write an LLVM backend to -generate code for a specific hardware or software target. -</p> - -</div> - -<div class="doc_subsection"> - <a name="Prerequisite">Prerequisite Reading</a> -</div> - -<div class="doc_text"> - -<p> -These essential documents must be read before reading this document: -</p> - -<ul> -<li><i><a href="http://www.llvm.org/docs/LangRef.html">LLVM Language Reference - Manual</a></i> — a reference manual for the LLVM assembly language.</li> - -<li><i><a href="http://www.llvm.org/docs/CodeGenerator.html">The LLVM - Target-Independent Code Generator</a></i> — a guide to the components - (classes and code generation algorithms) for translating the LLVM internal - representation into machine code for a specified target. Pay particular - attention to the descriptions of code generation stages: Instruction - Selection, Scheduling and Formation, SSA-based Optimization, Register - Allocation, Prolog/Epilog Code Insertion, Late Machine Code Optimizations, - and Code Emission.</li> - -<li><i><a href="http://www.llvm.org/docs/TableGenFundamentals.html">TableGen - Fundamentals</a></i> —a document that describes the TableGen - (<tt>tblgen</tt>) application that manages domain-specific information to - support LLVM code generation. TableGen processes input from a target - description file (<tt>.td</tt> suffix) and generates C++ code that can be - used for code generation.</li> - -<li><i><a href="http://www.llvm.org/docs/WritingAnLLVMPass.html">Writing an LLVM - Pass</a></i> — The assembly printer is a <tt>FunctionPass</tt>, as are - several SelectionDAG processing steps.</li> -</ul> - -<p> -To follow the SPARC examples in this document, have a copy of -<i><a href="http://www.sparc.org/standards/V8.pdf">The SPARC Architecture -Manual, Version 8</a></i> for reference. For details about the ARM instruction -set, refer to the <i><a href="http://infocenter.arm.com/">ARM Architecture -Reference Manual</a></i>. For more about the GNU Assembler format -(<tt>GAS</tt>), see -<i><a href="http://sourceware.org/binutils/docs/as/index.html">Using As</a></i>, -especially for the assembly printer. <i>Using As</i> contains a list of target -machine dependent features. -</p> - -</div> - -<div class="doc_subsection"> - <a name="Basic">Basic Steps</a> -</div> - -<div class="doc_text"> - -<p> -To write a compiler backend for LLVM that converts the LLVM IR to code for a -specified target (machine or other language), follow these steps: -</p> - -<ul> -<li>Create a subclass of the TargetMachine class that describes characteristics - of your target machine. Copy existing examples of specific TargetMachine - class and header files; for example, start with - <tt>SparcTargetMachine.cpp</tt> and <tt>SparcTargetMachine.h</tt>, but - change the file names for your target. Similarly, change code that - references "Sparc" to reference your target. </li> - -<li>Describe the register set of the target. Use TableGen to generate code for - register definition, register aliases, and register classes from a - target-specific <tt>RegisterInfo.td</tt> input file. You should also write - additional code for a subclass of the TargetRegisterInfo class that - represents the class register file data used for register allocation and - also describes the interactions between registers.</li> - -<li>Describe the instruction set of the target. Use TableGen to generate code - for target-specific instructions from target-specific versions of - <tt>TargetInstrFormats.td</tt> and <tt>TargetInstrInfo.td</tt>. You should - write additional code for a subclass of the TargetInstrInfo class to - represent machine instructions supported by the target machine. </li> - -<li>Describe the selection and conversion of the LLVM IR from a Directed Acyclic - Graph (DAG) representation of instructions to native target-specific - instructions. Use TableGen to generate code that matches patterns and - selects instructions based on additional information in a target-specific - version of <tt>TargetInstrInfo.td</tt>. Write code - for <tt>XXXISelDAGToDAG.cpp</tt>, where XXX identifies the specific target, - to perform pattern matching and DAG-to-DAG instruction selection. Also write - code in <tt>XXXISelLowering.cpp</tt> to replace or remove operations and - data types that are not supported natively in a SelectionDAG. </li> - -<li>Write code for an assembly printer that converts LLVM IR to a GAS format for - your target machine. You should add assembly strings to the instructions - defined in your target-specific version of <tt>TargetInstrInfo.td</tt>. You - should also write code for a subclass of AsmPrinter that performs the - LLVM-to-assembly conversion and a trivial subclass of TargetAsmInfo.</li> - -<li>Optionally, add support for subtargets (i.e., variants with different - capabilities). You should also write code for a subclass of the - TargetSubtarget class, which allows you to use the <tt>-mcpu=</tt> - and <tt>-mattr=</tt> command-line options.</li> - -<li>Optionally, add JIT support and create a machine code emitter (subclass of - TargetJITInfo) that is used to emit binary code directly into memory. </li> -</ul> - -<p> -In the <tt>.cpp</tt> and <tt>.h</tt>. files, initially stub up these methods and -then implement them later. Initially, you may not know which private members -that the class will need and which components will need to be subclassed. -</p> - -</div> - -<div class="doc_subsection"> - <a name="Preliminaries">Preliminaries</a> -</div> - -<div class="doc_text"> - -<p> -To actually create your compiler backend, you need to create and modify a few -files. The absolute minimum is discussed here. But to actually use the LLVM -target-independent code generator, you must perform the steps described in -the <a href="http://www.llvm.org/docs/CodeGenerator.html">LLVM -Target-Independent Code Generator</a> document. -</p> - -<p> -First, you should create a subdirectory under <tt>lib/Target</tt> to hold all -the files related to your target. If your target is called "Dummy," create the -directory <tt>lib/Target/Dummy</tt>. -</p> - -<p> -In this new -directory, create a <tt>Makefile</tt>. It is easiest to copy a -<tt>Makefile</tt> of another target and modify it. It should at least contain -the <tt>LEVEL</tt>, <tt>LIBRARYNAME</tt> and <tt>TARGET</tt> variables, and then -include <tt>$(LEVEL)/Makefile.common</tt>. The library can be -named <tt>LLVMDummy</tt> (for example, see the MIPS target). Alternatively, you -can split the library into <tt>LLVMDummyCodeGen</tt> -and <tt>LLVMDummyAsmPrinter</tt>, the latter of which should be implemented in a -subdirectory below <tt>lib/Target/Dummy</tt> (for example, see the PowerPC -target). -</p> - -<p> -Note that these two naming schemes are hardcoded into <tt>llvm-config</tt>. -Using any other naming scheme will confuse <tt>llvm-config</tt> and produce a -lot of (seemingly unrelated) linker errors when linking <tt>llc</tt>. -</p> - -<p> -To make your target actually do something, you need to implement a subclass of -<tt>TargetMachine</tt>. This implementation should typically be in the file -<tt>lib/Target/DummyTargetMachine.cpp</tt>, but any file in -the <tt>lib/Target</tt> directory will be built and should work. To use LLVM's -target independent code generator, you should do what all current machine -backends do: create a subclass of <tt>LLVMTargetMachine</tt>. (To create a -target from scratch, create a subclass of <tt>TargetMachine</tt>.) -</p> - -<p> -To get LLVM to actually build and link your target, you need to add it to -the <tt>TARGETS_TO_BUILD</tt> variable. To do this, you modify the configure -script to know about your target when parsing the <tt>--enable-targets</tt> -option. Search the configure script for <tt>TARGETS_TO_BUILD</tt>, add your -target to the lists there (some creativity required), and then -reconfigure. Alternatively, you can change <tt>autotools/configure.ac</tt> and -regenerate configure by running <tt>./autoconf/AutoRegen.sh</tt>. -</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="TargetMachine">Target Machine</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p> -<tt>LLVMTargetMachine</tt> is designed as a base class for targets implemented -with the LLVM target-independent code generator. The <tt>LLVMTargetMachine</tt> -class should be specialized by a concrete target class that implements the -various virtual methods. <tt>LLVMTargetMachine</tt> is defined as a subclass of -<tt>TargetMachine</tt> in <tt>include/llvm/Target/TargetMachine.h</tt>. The -<tt>TargetMachine</tt> class implementation (<tt>TargetMachine.cpp</tt>) also -processes numerous command-line options. -</p> - -<p> -To create a concrete target-specific subclass of <tt>LLVMTargetMachine</tt>, -start by copying an existing <tt>TargetMachine</tt> class and header. You -should name the files that you create to reflect your specific target. For -instance, for the SPARC target, name the files <tt>SparcTargetMachine.h</tt> and -<tt>SparcTargetMachine.cpp</tt>. -</p> - -<p> -For a target machine <tt>XXX</tt>, the implementation of -<tt>XXXTargetMachine</tt> must have access methods to obtain objects that -represent target components. These methods are named <tt>get*Info</tt>, and are -intended to obtain the instruction set (<tt>getInstrInfo</tt>), register set -(<tt>getRegisterInfo</tt>), stack frame layout (<tt>getFrameInfo</tt>), and -similar information. <tt>XXXTargetMachine</tt> must also implement the -<tt>getTargetData</tt> method to access an object with target-specific data -characteristics, such as data type size and alignment requirements. -</p> - -<p> -For instance, for the SPARC target, the header file -<tt>SparcTargetMachine.h</tt> declares prototypes for several <tt>get*Info</tt> -and <tt>getTargetData</tt> methods that simply return a class member. -</p> - -<div class="doc_code"> -<pre> -namespace llvm { - -class Module; - -class SparcTargetMachine : public LLVMTargetMachine { - const TargetData DataLayout; // Calculates type size & alignment - SparcSubtarget Subtarget; - SparcInstrInfo InstrInfo; - TargetFrameInfo FrameInfo; - -protected: - virtual const TargetAsmInfo *createTargetAsmInfo() const; - -public: - SparcTargetMachine(const Module &M, const std::string &FS); - - virtual const SparcInstrInfo *getInstrInfo() const {return &InstrInfo; } - virtual const TargetFrameInfo *getFrameInfo() const {return &FrameInfo; } - virtual const TargetSubtarget *getSubtargetImpl() const{return &Subtarget; } - virtual const TargetRegisterInfo *getRegisterInfo() const { - return &InstrInfo.getRegisterInfo(); - } - virtual const TargetData *getTargetData() const { return &DataLayout; } - static unsigned getModuleMatchQuality(const Module &M); - - // Pass Pipeline Configuration - virtual bool addInstSelector(PassManagerBase &PM, bool Fast); - virtual bool addPreEmitPass(PassManagerBase &PM, bool Fast); -}; - -} // end namespace llvm -</pre> -</div> - -</div> - - -<div class="doc_text"> - -<ul> -<li><tt>getInstrInfo()</tt></li> -<li><tt>getRegisterInfo()</tt></li> -<li><tt>getFrameInfo()</tt></li> -<li><tt>getTargetData()</tt></li> -<li><tt>getSubtargetImpl()</tt></li> -</ul> - -<p>For some targets, you also need to support the following methods:</p> - -<ul> -<li><tt>getTargetLowering()</tt></li> -<li><tt>getJITInfo()</tt></li> -</ul> - -<p> -In addition, the <tt>XXXTargetMachine</tt> constructor should specify a -<tt>TargetDescription</tt> string that determines the data layout for the target -machine, including characteristics such as pointer size, alignment, and -endianness. For example, the constructor for SparcTargetMachine contains the -following: -</p> - -<div class="doc_code"> -<pre> -SparcTargetMachine::SparcTargetMachine(const Module &M, const std::string &FS) - : DataLayout("E-p:32:32-f128:128:128"), - Subtarget(M, FS), InstrInfo(Subtarget), - FrameInfo(TargetFrameInfo::StackGrowsDown, 8, 0) { -} -</pre> -</div> - -</div> - -<div class="doc_text"> - -<p>Hyphens separate portions of the <tt>TargetDescription</tt> string.</p> - -<ul> -<li>An upper-case "<tt>E</tt>" in the string indicates a big-endian target data - model. a lower-case "<tt>e</tt>" indicates little-endian.</li> - -<li>"<tt>p:</tt>" is followed by pointer information: size, ABI alignment, and - preferred alignment. If only two figures follow "<tt>p:</tt>", then the - first value is pointer size, and the second value is both ABI and preferred - alignment.</li> - -<li>Then a letter for numeric type alignment: "<tt>i</tt>", "<tt>f</tt>", - "<tt>v</tt>", or "<tt>a</tt>" (corresponding to integer, floating point, - vector, or aggregate). "<tt>i</tt>", "<tt>v</tt>", or "<tt>a</tt>" are - followed by ABI alignment and preferred alignment. "<tt>f</tt>" is followed - by three values: the first indicates the size of a long double, then ABI - alignment, and then ABI preferred alignment.</li> -</ul> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="TargetRegistration">Target Registration</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p> -You must also register your target with the <tt>TargetRegistry</tt>, which is -what other LLVM tools use to be able to lookup and use your target at -runtime. The <tt>TargetRegistry</tt> can be used directly, but for most targets -there are helper templates which should take care of the work for you.</p> - -<p> -All targets should declare a global <tt>Target</tt> object which is used to -represent the target during registration. Then, in the target's TargetInfo -library, the target should define that object and use -the <tt>RegisterTarget</tt> template to register the target. For example, the Sparc registration code looks like this: -</p> - -<div class="doc_code"> -<pre> -Target llvm::TheSparcTarget; - -extern "C" void LLVMInitializeSparcTargetInfo() { - RegisterTarget<Triple::sparc, /*HasJIT=*/false> - X(TheSparcTarget, "sparc", "Sparc"); -} -</pre> -</div> - -<p> -This allows the <tt>TargetRegistry</tt> to look up the target by name or by -target triple. In addition, most targets will also register additional features -which are available in separate libraries. These registration steps are -separate, because some clients may wish to only link in some parts of the target --- the JIT code generator does not require the use of the assembler printer, for -example. Here is an example of registering the Sparc assembly printer: -</p> - -<div class="doc_code"> -<pre> -extern "C" void LLVMInitializeSparcAsmPrinter() { - RegisterAsmPrinter<SparcAsmPrinter> X(TheSparcTarget); -} -</pre> -</div> - -<p> -For more information, see -"<a href="/doxygen/TargetRegistry_8h-source.html">llvm/Target/TargetRegistry.h</a>". -</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="RegisterSet">Register Set and Register Classes</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p> -You should describe a concrete target-specific class that represents the -register file of a target machine. This class is called <tt>XXXRegisterInfo</tt> -(where <tt>XXX</tt> identifies the target) and represents the class register -file data that is used for register allocation. It also describes the -interactions between registers. -</p> - -<p> -You also need to define register classes to categorize related registers. A -register class should be added for groups of registers that are all treated the -same way for some instruction. Typical examples are register classes for -integer, floating-point, or vector registers. A register allocator allows an -instruction to use any register in a specified register class to perform the -instruction in a similar manner. Register classes allocate virtual registers to -instructions from these sets, and register classes let the target-independent -register allocator automatically choose the actual registers. -</p> - -<p> -Much of the code for registers, including register definition, register aliases, -and register classes, is generated by TableGen from <tt>XXXRegisterInfo.td</tt> -input files and placed in <tt>XXXGenRegisterInfo.h.inc</tt> and -<tt>XXXGenRegisterInfo.inc</tt> output files. Some of the code in the -implementation of <tt>XXXRegisterInfo</tt> requires hand-coding. -</p> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="RegisterDef">Defining a Register</a> -</div> - -<div class="doc_text"> - -<p> -The <tt>XXXRegisterInfo.td</tt> file typically starts with register definitions -for a target machine. The <tt>Register</tt> class (specified -in <tt>Target.td</tt>) is used to define an object for each register. The -specified string <tt>n</tt> becomes the <tt>Name</tt> of the register. The -basic <tt>Register</tt> object does not have any subregisters and does not -specify any aliases. -</p> - -<div class="doc_code"> -<pre> -class Register<string n> { - string Namespace = ""; - string AsmName = n; - string Name = n; - int SpillSize = 0; - int SpillAlignment = 0; - list<Register> Aliases = []; - list<Register> SubRegs = []; - list<int> DwarfNumbers = []; -} -</pre> -</div> - -<p> -For example, in the <tt>X86RegisterInfo.td</tt> file, there are register -definitions that utilize the Register class, such as: -</p> - -<div class="doc_code"> -<pre> -def AL : Register<"AL">, DwarfRegNum<[0, 0, 0]>; -</pre> -</div> - -<p> -This defines the register <tt>AL</tt> and assigns it values (with -<tt>DwarfRegNum</tt>) that are used by <tt>gcc</tt>, <tt>gdb</tt>, or a debug -information writer to identify a register. For register -<tt>AL</tt>, <tt>DwarfRegNum</tt> takes an array of 3 values representing 3 -different modes: the first element is for X86-64, the second for exception -handling (EH) on X86-32, and the third is generic. -1 is a special Dwarf number -that indicates the gcc number is undefined, and -2 indicates the register number -is invalid for this mode. -</p> - -<p> -From the previously described line in the <tt>X86RegisterInfo.td</tt> file, -TableGen generates this code in the <tt>X86GenRegisterInfo.inc</tt> file: -</p> - -<div class="doc_code"> -<pre> -static const unsigned GR8[] = { X86::AL, ... }; - -const unsigned AL_AliasSet[] = { X86::AX, X86::EAX, X86::RAX, 0 }; - -const TargetRegisterDesc RegisterDescriptors[] = { - ... -{ "AL", "AL", AL_AliasSet, Empty_SubRegsSet, Empty_SubRegsSet, AL_SuperRegsSet }, ... -</pre> -</div> - -<p> -From the register info file, TableGen generates a <tt>TargetRegisterDesc</tt> -object for each register. <tt>TargetRegisterDesc</tt> is defined in -<tt>include/llvm/Target/TargetRegisterInfo.h</tt> with the following fields: -</p> - -<div class="doc_code"> -<pre> -struct TargetRegisterDesc { - const char *AsmName; // Assembly language name for the register - const char *Name; // Printable name for the reg (for debugging) - const unsigned *AliasSet; // Register Alias Set - const unsigned *SubRegs; // Sub-register set - const unsigned *ImmSubRegs; // Immediate sub-register set - const unsigned *SuperRegs; // Super-register set -};</pre> -</div> - -<p> -TableGen uses the entire target description file (<tt>.td</tt>) to determine -text names for the register (in the <tt>AsmName</tt> and <tt>Name</tt> fields of -<tt>TargetRegisterDesc</tt>) and the relationships of other registers to the -defined register (in the other <tt>TargetRegisterDesc</tt> fields). In this -example, other definitions establish the registers "<tt>AX</tt>", -"<tt>EAX</tt>", and "<tt>RAX</tt>" as aliases for one another, so TableGen -generates a null-terminated array (<tt>AL_AliasSet</tt>) for this register alias -set. -</p> - -<p> -The <tt>Register</tt> class is commonly used as a base class for more complex -classes. In <tt>Target.td</tt>, the <tt>Register</tt> class is the base for the -<tt>RegisterWithSubRegs</tt> class that is used to define registers that need to -specify subregisters in the <tt>SubRegs</tt> list, as shown here: -</p> - -<div class="doc_code"> -<pre> -class RegisterWithSubRegs<string n, -list<Register> subregs> : Register<n> { - let SubRegs = subregs; -} -</pre> -</div> - -<p> -In <tt>SparcRegisterInfo.td</tt>, additional register classes are defined for -SPARC: a Register subclass, SparcReg, and further subclasses: <tt>Ri</tt>, -<tt>Rf</tt>, and <tt>Rd</tt>. SPARC registers are identified by 5-bit ID -numbers, which is a feature common to these subclasses. Note the use of -'<tt>let</tt>' expressions to override values that are initially defined in a -superclass (such as <tt>SubRegs</tt> field in the <tt>Rd</tt> class). -</p> - -<div class="doc_code"> -<pre> -class SparcReg<string n> : Register<n> { - field bits<5> Num; - let Namespace = "SP"; -} -// Ri - 32-bit integer registers -class Ri<bits<5> num, string n> : -SparcReg<n> { - let Num = num; -} -// Rf - 32-bit floating-point registers -class Rf<bits<5> num, string n> : -SparcReg<n> { - let Num = num; -} -// Rd - Slots in the FP register file for 64-bit -floating-point values. -class Rd<bits<5> num, string n, -list<Register> subregs> : SparcReg<n> { - let Num = num; - let SubRegs = subregs; -} -</pre> -</div> - -<p> -In the <tt>SparcRegisterInfo.td</tt> file, there are register definitions that -utilize these subclasses of <tt>Register</tt>, such as: -</p> - -<div class="doc_code"> -<pre> -def G0 : Ri< 0, "G0">, -DwarfRegNum<[0]>; -def G1 : Ri< 1, "G1">, DwarfRegNum<[1]>; -... -def F0 : Rf< 0, "F0">, -DwarfRegNum<[32]>; -def F1 : Rf< 1, "F1">, -DwarfRegNum<[33]>; -... -def D0 : Rd< 0, "F0", [F0, F1]>, -DwarfRegNum<[32]>; -def D1 : Rd< 2, "F2", [F2, F3]>, -DwarfRegNum<[34]>; -</pre> -</div> - -<p> -The last two registers shown above (<tt>D0</tt> and <tt>D1</tt>) are -double-precision floating-point registers that are aliases for pairs of -single-precision floating-point sub-registers. In addition to aliases, the -sub-register and super-register relationships of the defined register are in -fields of a register's TargetRegisterDesc. -</p> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="RegisterClassDef">Defining a Register Class</a> -</div> - -<div class="doc_text"> - -<p> -The <tt>RegisterClass</tt> class (specified in <tt>Target.td</tt>) is used to -define an object that represents a group of related registers and also defines -the default allocation order of the registers. A target description file -<tt>XXXRegisterInfo.td</tt> that uses <tt>Target.td</tt> can construct register -classes using the following class: -</p> - -<div class="doc_code"> -<pre> -class RegisterClass<string namespace, -list<ValueType> regTypes, int alignment, - list<Register> regList> { - string Namespace = namespace; - list<ValueType> RegTypes = regTypes; - int Size = 0; // spill size, in bits; zero lets tblgen pick the size - int Alignment = alignment; - - // CopyCost is the cost of copying a value between two registers - // default value 1 means a single instruction - // A negative value means copying is extremely expensive or impossible - int CopyCost = 1; - list<Register> MemberList = regList; - - // for register classes that are subregisters of this class - list<RegisterClass> SubRegClassList = []; - - code MethodProtos = [{}]; // to insert arbitrary code - code MethodBodies = [{}]; -} -</pre> -</div> - -<p>To define a RegisterClass, use the following 4 arguments:</p> - -<ul> -<li>The first argument of the definition is the name of the namespace.</li> - -<li>The second argument is a list of <tt>ValueType</tt> register type values - that are defined in <tt>include/llvm/CodeGen/ValueTypes.td</tt>. Defined - values include integer types (such as <tt>i16</tt>, <tt>i32</tt>, - and <tt>i1</tt> for Boolean), floating-point types - (<tt>f32</tt>, <tt>f64</tt>), and vector types (for example, <tt>v8i16</tt> - for an <tt>8 x i16</tt> vector). All registers in a <tt>RegisterClass</tt> - must have the same <tt>ValueType</tt>, but some registers may store vector - data in different configurations. For example a register that can process a - 128-bit vector may be able to handle 16 8-bit integer elements, 8 16-bit - integers, 4 32-bit integers, and so on. </li> - -<li>The third argument of the <tt>RegisterClass</tt> definition specifies the - alignment required of the registers when they are stored or loaded to - memory.</li> - -<li>The final argument, <tt>regList</tt>, specifies which registers are in this - class. If an <tt>allocation_order_*</tt> method is not specified, - then <tt>regList</tt> also defines the order of allocation used by the - register allocator.</li> -</ul> - -<p> -In <tt>SparcRegisterInfo.td</tt>, three RegisterClass objects are defined: -<tt>FPRegs</tt>, <tt>DFPRegs</tt>, and <tt>IntRegs</tt>. For all three register -classes, the first argument defines the namespace with the string -'<tt>SP</tt>'. <tt>FPRegs</tt> defines a group of 32 single-precision -floating-point registers (<tt>F0</tt> to <tt>F31</tt>); <tt>DFPRegs</tt> defines -a group of 16 double-precision registers -(<tt>D0-D15</tt>). For <tt>IntRegs</tt>, the <tt>MethodProtos</tt> -and <tt>MethodBodies</tt> methods are used by TableGen to insert the specified -code into generated output. -</p> - -<div class="doc_code"> -<pre> -def FPRegs : RegisterClass<"SP", [f32], 32, - [F0, F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12, F13, F14, F15, - F16, F17, F18, F19, F20, F21, F22, F23, F24, F25, F26, F27, F28, F29, F30, F31]>; - -def DFPRegs : RegisterClass<"SP", [f64], 64, - [D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14, D15]>; - -def IntRegs : RegisterClass<"SP", [i32], 32, - [L0, L1, L2, L3, L4, L5, L6, L7, - I0, I1, I2, I3, I4, I5, - O0, O1, O2, O3, O4, O5, O7, - G1, - // Non-allocatable regs: - G2, G3, G4, - O6, // stack ptr - I6, // frame ptr - I7, // return address - G0, // constant zero - G5, G6, G7 // reserved for kernel - ]> { - let MethodProtos = [{ - iterator allocation_order_end(const MachineFunction &MF) const; - }]; - let MethodBodies = [{ - IntRegsClass::iterator - IntRegsClass::allocation_order_end(const MachineFunction &MF) const { - return end() - 10 // Don't allocate special registers - -1; - } - }]; -} -</pre> -</div> - -<p> -Using <tt>SparcRegisterInfo.td</tt> with TableGen generates several output files -that are intended for inclusion in other source code that you write. -<tt>SparcRegisterInfo.td</tt> generates <tt>SparcGenRegisterInfo.h.inc</tt>, -which should be included in the header file for the implementation of the SPARC -register implementation that you write (<tt>SparcRegisterInfo.h</tt>). In -<tt>SparcGenRegisterInfo.h.inc</tt> a new structure is defined called -<tt>SparcGenRegisterInfo</tt> that uses <tt>TargetRegisterInfo</tt> as its -base. It also specifies types, based upon the defined register -classes: <tt>DFPRegsClass</tt>, <tt>FPRegsClass</tt>, and <tt>IntRegsClass</tt>. -</p> - -<p> -<tt>SparcRegisterInfo.td</tt> also generates <tt>SparcGenRegisterInfo.inc</tt>, -which is included at the bottom of <tt>SparcRegisterInfo.cpp</tt>, the SPARC -register implementation. The code below shows only the generated integer -registers and associated register classes. The order of registers -in <tt>IntRegs</tt> reflects the order in the definition of <tt>IntRegs</tt> in |