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diff --git a/docs/AdvancedGetElementPtr.html b/docs/AdvancedGetElementPtr.html deleted file mode 100644 index 1d37278..0000000 --- a/docs/AdvancedGetElementPtr.html +++ /dev/null @@ -1,362 +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>The Revenge Of The Often Misunderstood GEP Instruction</title> - <link rel="stylesheet" href="llvm.css" type="text/css"> - <style type="text/css"> - TABLE { text-align: left; border: 1px solid black; border-collapse: collapse; margin: 0 0 0 0; } - </style> -</head> -<body> - -<div class="doc_title"> - The Revenge Of The Often Misunderstood GEP Instruction -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"><a name="intro"><b>Introduction</b></a></div> -<!-- *********************************************************************** --> -<div class="doc_text"> - <p>GEP was mysterious and wily at first, but it turned out that the basic - workings were fairly comprehensible. However the dragon was merely subdued; - now it's back, and it has more fundamental complexity to confront. This - document seeks to uncover misunderstandings of the GEP operator that tend - to persist past initial confusion about the funky "extra 0" thing. Here we - show that the GEP instruction is really not quite as simple as it seems, - even after the initial confusion is overcome.</p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>How is GEP different from ptrtoint, arithmetic, - and inttoptr?</b></a> -</div> -<div class="doc_text"> - <p>It's very similar; there are only subtle differences.</p> - - <p>With ptrtoint, you have to pick an integer type. One approach is to pick i64; - this is safe on everything LLVM supports (LLVM internally assumes pointers - are never wider than 64 bits in many places), and the optimizer will actually - narrow the i64 arithmetic down to the actual pointer size on targets which - don't support 64-bit arithmetic in most cases. However, there are some cases - where it doesn't do this. With GEP you can avoid this problem. - - <p>Also, GEP carries additional pointer aliasing rules. It's invalid to take a - GEP from one object, address into a different separately allocated - object, and dereference it. IR producers (front-ends) must follow this rule, - and consumers (optimizers, specifically alias analysis) benefit from being - able to rely on it.</p> - - <p>And, GEP is more concise in common cases.</p> - - <p>However, for the underlying integer computation implied, there - is no difference.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>I'm writing a backend for a target which needs custom - lowering for GEP. How do I do this?</b></a> -</div> -<div class="doc_text"> - <p>You don't. The integer computation implied by a GEP is target-independent. - Typically what you'll need to do is make your backend pattern-match - expressions trees involving ADD, MUL, etc., which are what GEP is lowered - into. This has the advantage of letting your code work correctly in more - cases.</p> - - <p>GEP does use target-dependent parameters for the size and layout of data - types, which targets can customize.</p> - - <p>If you require support for addressing units which are not 8 bits, you'll - need to fix a lot of code in the backend, with GEP lowering being only a - small piece of the overall picture.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>Why do struct member indices always use i32?</b></a> -</div> -<div class="doc_text"> - <p>The specific type i32 is probably just a historical artifact, however it's - wide enough for all practical purposes, so there's been no need to change it. - It doesn't necessarily imply i32 address arithmetic; it's just an identifier - which identifies a field in a struct. Requiring that all struct indices be - the same reduces the range of possibilities for cases where two GEPs are - effectively the same but have distinct operand types.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>How does VLA addressing work with GEPs?</b></a> -</div> -<div class="doc_text"> - <p>GEPs don't natively support VLAs. LLVM's type system is entirely static, - and GEP address computations are guided by an LLVM type.</p> - - <p>VLA indices can be implemented as linearized indices. For example, an - expression like X[a][b][c], must be effectively lowered into a form - like X[a*m+b*n+c], so that it appears to the GEP as a single-dimensional - array reference.</p> - - <p>This means if you want to write an analysis which understands array - indices and you want to support VLAs, your code will have to be - prepared to reverse-engineer the linearization. One way to solve this - problem is to use the ScalarEvolution library, which always presents - VLA and non-VLA indexing in the same manner.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>What happens if an array index is out of bounds?</b></a> -</div> -<div class="doc_text"> - <p>There are two senses in which an array index can be out of bounds.</p> - - <p>First, there's the array type which comes from the (static) type of - the first operand to the GEP. Indices greater than the number of elements - in the corresponding static array type are valid. There is no problem with - out of bounds indices in this sense. Indexing into an array only depends - on the size of the array element, not the number of elements.</p> - - <p>A common example of how this is used is arrays where the size is not known. - It's common to use array types with zero length to represent these. The - fact that the static type says there are zero elements is irrelevant; it's - perfectly valid to compute arbitrary element indices, as the computation - only depends on the size of the array element, not the number of - elements. Note that zero-sized arrays are not a special case here.</p> - - <p>This sense is unconnected with <tt>inbounds</tt> keyword. The - <tt>inbounds</tt> keyword is designed to describe low-level pointer - arithmetic overflow conditions, rather than high-level array - indexing rules. - - <p>Analysis passes which wish to understand array indexing should not - assume that the static array type bounds are respected.</p> - - <p>The second sense of being out of bounds is computing an address that's - beyond the actual underlying allocated object.</p> - - <p>With the <tt>inbounds</tt> keyword, the result value of the GEP is - undefined if the address is outside the actual underlying allocated - object and not the address one-past-the-end.</p> - - <p>Without the <tt>inbounds</tt> keyword, there are no restrictions - on computing out-of-bounds addresses. Obviously, performing a load or - a store requires an address of allocated and sufficiently aligned - memory. But the GEP itself is only concerned with computing addresses.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>Can array indices be negative?</b></a> -</div> -<div class="doc_text"> - <p>Yes. This is basically a special case of array indices being out - of bounds.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>Can I compare two values computed with GEPs?</b></a> -</div> -<div class="doc_text"> - <p>Yes. If both addresses are within the same allocated object, or - one-past-the-end, you'll get the comparison result you expect. If either - is outside of it, integer arithmetic wrapping may occur, so the - comparison may not be meaningful.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>Can I do GEP with a different pointer type than the type of - the underlying object?</b></a> -</div> -<div class="doc_text"> - <p>Yes. There are no restrictions on bitcasting a pointer value to an arbitrary - pointer type. The types in a GEP serve only to define the parameters for the - underlying integer computation. They need not correspond with the actual - type of the underlying object.</p> - - <p>Furthermore, loads and stores don't have to use the same types as the type - of the underlying object. Types in this context serve only to specify - memory size and alignment. Beyond that there are merely a hint to the - optimizer indicating how the value will likely be used.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>Can I cast an object's address to integer and add it - to null?</b></a> -</div> -<div class="doc_text"> - <p>You can compute an address that way, but if you use GEP to do the add, - you can't use that pointer to actually access the object, unless the - object is managed outside of LLVM.</p> - - <p>The underlying integer computation is sufficiently defined; null has a - defined value -- zero -- and you can add whatever value you want to it.</p> - - <p>However, it's invalid to access (load from or store to) an LLVM-aware - object with such a pointer. This includes GlobalVariables, Allocas, and - objects pointed to by noalias pointers.</p> - - <p>If you really need this functionality, you can do the arithmetic with - explicit integer instructions, and use inttoptr to convert the result to - an address. Most of GEP's special aliasing rules do not apply to pointers - computed from ptrtoint, arithmetic, and inttoptr sequences.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>Can I compute the distance between two objects, and add - that value to one address to compute the other address?</b></a> -</div> -<div class="doc_text"> - <p>As with arithmetic on null, You can use GEP to compute an address that - way, but you can't use that pointer to actually access the object if you - do, unless the object is managed outside of LLVM.</p> - - <p>Also as above, ptrtoint and inttoptr provide an alternative way to do this - which do not have this restriction.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_subsection"> - <a name="lead0"><b>Can I do type-based alias analysis on LLVM IR?</b></a> -</div> -<div class="doc_text"> - <p>You can't do type-based alias analysis using LLVM's built-in type system, - because LLVM has no restrictions on mixing types in addressing, loads or - stores.</p> - - <p>It would be possible to add special annotations to the IR, probably using - metadata, to describe a different type system (such as the C type system), - and do type-based aliasing on top of that. This is a much bigger - undertaking though.</p> - -</div> - -<!-- *********************************************************************** --> - -<div class="doc_subsection"> - <a name="lead0"><b>What's an uglygep?</b></a> -</div> -<div class="doc_text"> - <p>Some LLVM optimizers operate on GEPs by internally lowering them into - more primitive integer expressions, which allows them to be combined - with other integer expressions and/or split into multiple separate - integer expressions. If they've made non-trivial changes, translating - back into LLVM IR can involve reverse-engineering the structure of - the addressing in order to fit it into the static type of the original - first operand. It isn't always possibly to fully reconstruct this - structure; sometimes the underlying addressing doesn't correspond with - the static type at all. In such cases the optimizer instead will emit - a GEP with the base pointer casted to a simple address-unit pointer, - using the name "uglygep". This isn't pretty, but it's just as - valid, and it's sufficient to preserve the pointer aliasing guarantees - that GEP provides.</p> - -</div> - -<!-- *********************************************************************** --> - -<div class="doc_subsection"> - <a name="lead0"><b>Can GEP index into vector elements?</b></a> -</div> -<div class="doc_text"> - <p>Sort of. This hasn't always been forcefully disallowed, though it's - not recommended. It leads to awkward special cases in the optimizers. - In the future, it may be outright disallowed.</p> - - <p>Instead, you should cast your pointer types and use arrays instead of - vectors for addressing. Arrays have the same in-memory representation - as vectors, so the addressing is interchangeable.</p> - -</div> - -<!-- *********************************************************************** --> - -<div class="doc_subsection"> - <a name="lead0"><b>Can GEP index into unions?</b></a> -</div> -<div class="doc_text"> - <p>Unknown.</p> - -</div> - -<!-- *********************************************************************** --> - -<div class="doc_subsection"> - <a name="lead0"><b>What happens if a GEP computation overflows?</b></a> -</div> -<div class="doc_text"> - <p>If the GEP has the <tt>inbounds</tt> keyword, the result value is - undefined.</p> - - <p>Otherwise, the result value is the result from evaluating the implied - two's complement integer computation. However, since there's no - guarantee of where an object will be allocated in the address space, - such values have limited meaning.</p> - -</div> - -<!-- *********************************************************************** --> - -<div class="doc_subsection"> - <a name="lead0"><b>What effect do address spaces have on GEPs?</b></a> -</div> -<div class="doc_text"> - <p>None, except that the address space qualifier on the first operand pointer - type always matches the address space qualifier on the result type.</p> - -</div> - -<!-- *********************************************************************** --> - -<div class="doc_subsection"> - <a name="lead0"><b>Why is GEP designed this way?</b></a> -</div> -<div class="doc_text"> - <p>The design of GEP has the following goals, in rough unofficial - order of priority:</p> - <ul> - <li>Support C, C-like languages, and languages which can be - conceptually lowered into C (this covers a lot).</li> - <li>Support optimizations such as those that are common in - C compilers.</li> - <li>Provide a consistent method for computing addresses so that - address computations don't need to be a part of load and - store instructions in the IR.</li> - <li>Support non-C-like languages, to the extent that it doesn't - interfere with other goals.</li> - <li>Minimize target-specific information in the IR.</li> - </ul> -</div> - -<!-- *********************************************************************** --> - -<hr> -<address> - <a href="http://jigsaw.w3.org/css-validator/check/referer"><img - src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a> - <a href="http://validator.w3.org/check/referer"><img - src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a> - <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br/> - Last modified: $Date: 2010-02-18 19:40:29 +0100 (Thu, 18 Feb 2010) $ -</address> -</body> -</html> - diff --git a/docs/CommandGuide/llvm-db.pod b/docs/CommandGuide/llvm-db.pod deleted file mode 100644 index 1324176..0000000 --- a/docs/CommandGuide/llvm-db.pod +++ /dev/null @@ -1,16 +0,0 @@ -=pod - -=head1 NAME - -llvm-db - LLVM debugger (alpha) - -=head1 SYNOPSIS - -Details coming soon. Please see -L<http://llvm.org/docs/SourceLevelDebugging.html> in the meantime. - -=head1 AUTHORS - -Maintained by the LLVM Team (L<http://llvm.org>). - -=cut diff --git a/docs/ReleaseNotes-2.6.html b/docs/ReleaseNotes-2.6.html deleted file mode 100644 index 64084cd..0000000 --- a/docs/ReleaseNotes-2.6.html +++ /dev/null @@ -1,784 +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"> - <link rel="stylesheet" href="llvm.css" type="text/css"> - <title>LLVM 2.6 Release Notes</title> -</head> -<body> - -<div class="doc_title">LLVM 2.6 Release Notes</div> - -<ol> - <li><a href="#intro">Introduction</a></li> - <li><a href="#subproj">Sub-project Status Update</a></li> - <li><a href="#externalproj">External Projects Using LLVM 2.6</a></li> - <li><a href="#whatsnew">What's New in LLVM 2.6?</a></li> - <li><a href="GettingStarted.html">Installation Instructions</a></li> - <li><a href="#portability">Portability and Supported Platforms</a></li> - <li><a href="#knownproblems">Known Problems</a></li> - <li><a href="#additionalinfo">Additional Information</a></li> -</ol> - -<div class="doc_author"> - <p>Written by the <a href="http://llvm.org">LLVM Team</a></p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="intro">Introduction</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p>This document contains the release notes for the LLVM Compiler -Infrastructure, release 2.6. Here we describe the status of LLVM, including -major improvements from the previous release and significant known problems. -All LLVM releases may be downloaded from the <a -href="http://llvm.org/releases/">LLVM releases web site</a>.</p> - -<p>For more information about LLVM, including information about the latest -release, please check out the <a href="http://llvm.org/">main LLVM -web site</a>. If you have questions or comments, the <a -href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's Mailing -List</a> is a good place to send them.</p> - -<p>Note that if you are reading this file from a Subversion checkout or the -main LLVM web page, this document applies to the <i>next</i> release, not the -current one. To see the release notes for a specific release, please see the -<a href="http://llvm.org/releases/">releases page</a>.</p> - -</div> - -<!-- Unfinished features in 2.5: - Machine LICM - Machine Sinking - target-specific intrinsics - gold lto plugin - pre-alloc splitter, strong phi elim - <tt>llc -enable-value-prop</tt>, propagation of value info - (sign/zero ext info) from one MBB to another - debug info for optimized code - interpreter + libffi - postalloc scheduler: anti dependence breaking, hazard recognizer? - -initial support for debug line numbers when optimization enabled, not useful in - 2.5 but will be for 2.6. - - --> - - <!-- for announcement email: - --> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="subproj">Sub-project Status Update</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> -<p> -The LLVM 2.6 distribution currently consists of code from the core LLVM -repository —which roughly includes the LLVM optimizers, code generators -and supporting tools — and the llvm-gcc repository. In addition to this -code, the LLVM Project includes other sub-projects that are in development. The -two which are the most actively developed are the <a href="#clang">Clang -Project</a> and the <a href="#vmkit">VMKit Project</a>. -</p> - -</div> - - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a> -</div> - -<div class="doc_text"> - -<p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build -a set of new 'LLVM native' front-end technologies for the LLVM optimizer and -code generator. While Clang is not included in the LLVM 2.6 release, it is -continuing to make major strides forward in all areas. Its C and Objective-C -parsing and code generation support is now very solid. For example, it is -capable of successfully building many real-world applications for X86-32 -and X86-64, -including the <a href="http://wiki.freebsd.org/BuildingFreeBSDWithClang">FreeBSD -kernel</a> and <a href="http://gcc.gnu.org/gcc-4.2/">gcc 4.2</a>. C++ is also -making <a href="http://clang.llvm.org/cxx_status.html">incredible progress</a>, -and work on templates has recently started. If you are -interested in fast compiles and good diagnostics, we encourage you to try it out -by <a href="http://clang.llvm.org/get_started.html">building from mainline</a> -and reporting any issues you hit to the <a -href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">Clang front-end mailing -list</a>.</p> - -<p>In the LLVM 2.6 time-frame, the Clang team has made many improvements:</p> - -<ul> -<li>Something wonderful!</li> -<li>Many many bugs are fixed and many features have been added.</li> -</ul> -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="clangsa">Clang Static Analyzer</a> -</div> - -<div class="doc_text"> - -<p>Previously announced in the 2.4 LLVM release, the Clang project also -includes an early stage static source code analysis tool for <a -href="http://clang.llvm.org/StaticAnalysis.html">automatically finding bugs</a> -in C and Objective-C programs. The tool performs a growing set of checks to find -bugs that occur on a specific path within a program.</p> - -<p>In the LLVM 2.6 time-frame there have been many significant improvements to -XYZ.</p> - -<p>The set of checks performed by the static analyzer continues to expand, and -future plans for the tool include full source-level inter-procedural analysis -and deeper checks such as buffer overrun detection. There are many opportunities -to extend and enhance the static analyzer, and anyone interested in working on -this project is encouraged to get involved!</p> - -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a> -</div> - -<div class="doc_text"> -<p> -The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of -a JVM and a CLI Virtual Machines (Microsoft .NET is an -implementation of the CLI) using the Just-In-Time compiler of LLVM.</p> - -<p>Following LLVM 2.6, VMKit has its XYZ release that you can find on its -<a href="http://vmkit.llvm.org/releases/">webpage</a>. The release includes -bug fixes, cleanup and new features. The major changes are:</p> - -<ul> - -<li>Something wonderful!</li> - -</ul> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="externalproj">External Projects Using LLVM 2.6</a> -</div> -<!-- *********************************************************************** --> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="pure">Pure</a> -</div> - -<div class="doc_text"> -<p> -<a href="http://pure-lang.googlecode.com/">Pure</a> -is an algebraic/functional programming language based on term rewriting. -Programs are collections of equations which are used to evaluate expressions in -a symbolic fashion. Pure offers dynamic typing, eager and lazy evaluation, -lexical closures, a hygienic macro system (also based on term rewriting), -built-in list and matrix support (including list and matrix comprehensions) and -an easy-to-use C interface. The interpreter uses LLVM as a backend to - JIT-compile Pure programs to fast native code.</p> - -<p>In addition to the usual algebraic data structures, Pure also has -MATLAB-style matrices in order to support numeric computations and signal -processing in an efficient way. Pure is mainly aimed at mathematical -applications right now, but it has been designed as a general purpose language. -The dynamic interpreter environment and the C interface make it possible to use -it as a kind of functional scripting language for many application areas. -</p> -</div> - - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="ldc">LLVM D Compiler</a> -</div> - -<div class="doc_text"> -<p> -<a href="http://www.dsource.org/projects/ldc">LDC</a> is an implementation of -the D Programming Language using the LLVM optimizer and code generator. -The LDC project works great with the LLVM 2.6 release. General improvements in -this -cycle have included new inline asm constraint handling, better debug info -support, general bugfixes, and better x86-64 support. This has allowed -some major improvements in LDC, getting us much closer to being as -fully featured as the original DMD compiler from DigitalMars. -</p> -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="RoadsendPHP">Roadsend PHP</a> -</div> - -<div class="doc_text"> -<p><a href="http://code.roadsend.com/rphp">Roadsend PHP</a> (rphp) is an open -source implementation of the PHP programming -language that uses LLVM for its optimizer, JIT, and static compiler. This is a -reimplementation of an earlier project that is now based on LLVM.</p> -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="Unladen Swallow">Unladen Swallow</a> -</div> - -<div class="doc_text"> -<p><a href="http://code.google.com/p/unladen-swallow/">Unladen Swallow</a> is a -branch of <a href="http://python.org/">Python</a> intended to be fully -compatible and significantly faster. It uses LLVM's optimization passes and JIT -compiler.</p> -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="Rubinius">Rubinius</a> -</div> - -<div class="doc_text"> -<p><a href="http://github.com/evanphx/rubinius">Rubinius</a> is a new virtual -machine for Ruby. It leverages LLVM to dynamically compile Ruby code down to -machine code using LLVM's JIT.</p> -</div> - - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="whatsnew">What's New in LLVM 2.6?</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p>This release includes a huge number of bug fixes, performance tweaks, and -minor improvements. Some of the major improvements and new features are listed -in this section. -</p> -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="majorfeatures">Major New Features</a> -</div> - -<div class="doc_text"> - -<p>LLVM 2.6 includes several major new capabilities:</p> - -<ul> -<li>Something wonderful!</li> -</ul> - -</div> - - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="llvm-gcc">llvm-gcc 4.2 Improvements</a> -</div> - -<div class="doc_text"> - -<p>LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC -front-ends and driver with the LLVM optimizer and code generator. It currently -includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.</p> - -<ul> -<li>Something wonderful!</li> -</ul> - -</div> - - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="coreimprovements">LLVM IR and Core Improvements</a> -</div> - -<div class="doc_text"> -<p>LLVM IR has several new features that are used by our existing front-ends and -can be useful if you are writing a front-end for LLVM:</p> - -<ul> -<li>Something wonderful!</li> -</ul> - -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="optimizer">Optimizer Improvements</a> -</div> - -<div class="doc_text"> - -<p>In addition to a large array of bug fixes and minor performance tweaks, this -release includes a few major enhancements and additions to the optimizers:</p> - -<ul> - -<li>Something wonderful!</li> - -</ul> - -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="codegen">Target Independent Code Generator Improvements</a> -</div> - -<div class="doc_text"> - -<p>We have put a significant amount of work into the code generator -infrastructure, which allows us to implement more aggressive algorithms and make -it run faster:</p> - -<ul> - -<li>Something wonderful!</li> -</ul> -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="x86">X86-32 and X86-64 Target Improvements</a> -</div> - -<div class="doc_text"> -<p>New features of the X86 target include: -</p> - -<ul> - -<li>Something wonderful!</li> -</ul> - -</div> - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="pic16">PIC16 Target Improvements</a> -</div> - -<div class="doc_text"> -<p>New features of the PIC16 target include: -</p> - -<ul> -<li>Something wonderful!</li> -</ul> - -<p>Things not yet supported:</p> - -<ul> -<li>Floating point.</li> -<li>Passing/returning aggregate types to and from functions.</li> -<li>Variable arguments.</li> -<li>Indirect function calls.</li> -<li>Interrupts/programs.</li> -<li>Debug info.</li> -</ul> - -</div> - - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="llvmc">Improvements in LLVMC</a> -</div> - -<div class="doc_text"> -<p>New features include:</p> - -<ul> -<li>Something wonderful!</li> -</ul> - -</div> - - -<!--=========================================================================--> -<div class="doc_subsection"> -<a name="changes">Major Changes and Removed Features</a> -</div> - -<div class="doc_text"> - -<p>If you're already an LLVM user or developer with out-of-tree changes based -on LLVM 2.5, this section lists some "gotchas" that you may run into upgrading -from the previous release.</p> - -<ul> - -<li>Something horrible!</li> - -</ul> - - -<p>In addition, many APIs have changed in this release. Some of the major LLVM -API changes are:</p> - -<ul> -<li>LLVM's global uniquing tables for <tt>Type</tt>s and <tt>Constant</tt>s have - been privatized into members of an <tt>LLVMContext</tt>. A number of APIs - now take an <tt>LLVMContext</tt> as a parameter. To smooth the transition - for clients that will only ever use a single context, the new - <tt>getGlobalContext()</tt> API can be used to access a default global - context which can be passed in any and all cases where a context is - required. -<li>The <tt>getABITypeSize</tt> methods are now called <tt>getAllocSize</tt>.</li> -</ul> - -</div> - - - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="portability">Portability and Supported Platforms</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p>LLVM is known to work on the following platforms:</p> - -<ul> -<li>Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat -Linux, Fedora Core and FreeBSD (and probably other unix-like systems).</li> -<li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit -and 64-bit modes.</li> -<li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li> -<li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited - support is available for native builds with Visual C++).</li> -<li>Sun UltraSPARC workstations running Solaris 10.</li> -<li>Alpha-based machines running Debian GNU/Linux.</li> -<li>Itanium-based (IA64) machines running Linux and HP-UX.</li> -</ul> - -<p>The core LLVM infrastructure uses GNU autoconf to adapt itself -to the machine and operating system on which it is built. However, minor -porting may be required to get LLVM to work on new platforms. We welcome your -portability patches and reports of successful builds or error messages.</p> - -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="knownproblems">Known Problems</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p>This section contains significant known problems with the LLVM system, -listed by component. If you run into a problem, please check the <a -href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if -there isn't already one.</p> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="experimental">Experimental features included with this release</a> -</div> - -<div class="doc_text"> - -<p>The following components of this LLVM release are either untested, known to -be broken or unreliable, or are in early development. These components should -not be relied on, and bugs should not be filed against them, but they may be -useful to some people. In particular, if you would like to work on one of these -components, please contact us on the <a -href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p> - -<ul> -<li>The MSIL, IA64, Alpha, SPU, MIPS, and PIC16 backends are experimental.</li> -<li>The <tt>llc</tt> "<tt>-filetype=asm</tt>" (the default) is the only - supported value for this option.</li> -</ul> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="x86-be">Known problems with the X86 back-end</a> -</div> - -<div class="doc_text"> - -<ul> - <li>The X86 backend does not yet support - all <a href="http://llvm.org/PR879">inline assembly that uses the X86 - floating point stack</a>. It supports the 'f' and 't' constraints, but not - 'u'.</li> - <li>The X86 backend generates inefficient floating point code when configured - to generate code for systems that don't have SSE2.</li> - <li>Win64 code generation wasn't widely tested. Everything should work, but we - expect small issues to happen. Also, llvm-gcc cannot build the mingw64 - runtime currently due - to <a href="http://llvm.org/PR2255">several</a> - <a href="http://llvm.org/PR2257">bugs</a> and due to lack of support for - the - 'u' inline assembly constraint and for X87 floating point inline assembly.</li> - <li>The X86-64 backend does not yet support the LLVM IR instruction - <tt>va_arg</tt>. Currently, the llvm-gcc and front-ends support variadic - argument constructs on X86-64 by lowering them manually.</li> -</ul> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="ppc-be">Known problems with the PowerPC back-end</a> -</div> - -<div class="doc_text"> - -<ul> -<li>The Linux PPC32/ABI support needs testing for the interpreter and static -compilation, and lacks support for debug information.</li> -</ul> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="arm-be">Known problems with the ARM back-end</a> -</div> - -<div class="doc_text"> - -<ul> -<li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6 -processors, thumb programs can crash or produce wrong -results (<a href="http://llvm.org/PR1388">PR1388</a>).</li> -<li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested. -</li> -<li>There is a bug in QEMU-ARM (<= 0.9.0) which causes it to incorrectly - execute -programs compiled with LLVM. Please use more recent versions of QEMU.</li> -</ul> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="sparc-be">Known problems with the SPARC back-end</a> -</div> - -<div class="doc_text"> - -<ul> -<li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not - support the 64-bit SPARC ABI (-m64).</li> -</ul> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="mips-be">Known problems with the MIPS back-end</a> -</div> - -<div class="doc_text"> - -<ul> -<li>The O32 ABI is not fully supported.</li> -<li>64-bit MIPS targets are not supported yet.</li> -</ul> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="alpha-be">Known problems with the Alpha back-end</a> -</div> - -<div class="doc_text"> - -<ul> - -<li>On 21164s, some rare FP arithmetic sequences which may trap do not have the -appropriate nops inserted to ensure restartability.</li> - -</ul> -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="ia64-be">Known problems with the IA64 back-end</a> -</div> - -<div class="doc_text"> - -<ul> -<li>The Itanium backend is highly experimental and has a number of known - issues. We are looking for a maintainer for the Itanium backend. If you - are interested, please contact the LLVMdev mailing list.</li> -</ul> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="c-be">Known problems with the C back-end</a> -</div> - -<div class="doc_text"> - -<ul> -<li><a href="http://llvm.org/PR802">The C backend has only basic support for - inline assembly code</a>.</li> -<li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common - C++ programs</a>, preventing intermixing between C++ compiled by the CBE and - C++ code compiled with <tt>llc</tt> or native compilers.</li> -<li>The C backend does not support all exception handling constructs.</li> -<li>The C backend does not support arbitrary precision integers.</li> -</ul> - -</div> - - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="c-fe">Known problems with the llvm-gcc C front-end</a> -</div> - -<div class="doc_text"> - -<p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time -Optimization</a> on most platforms "out-of-the-box". Please inquire on the -LLVMdev mailing list if you are interested.</p> - -<p>The only major language feature of GCC not supported by llvm-gcc is - the <tt>__builtin_apply</tt> family of builtins. However, some extensions - are only supported on some targets. For example, trampolines are only - supported on some targets (these are used when you take the address of a - nested function).</p> - -<p>If you run into GCC extensions which are not supported, please let us know. -</p> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="c++-fe">Known problems with the llvm-gcc C++ front-end</a> -</div> - -<div class="doc_text"> - -<p>The C++ front-end is considered to be fully -tested and works for a number of non-trivial programs, including LLVM -itself, Qt, Mozilla, etc.</p> - -<ul> -<li>Exception handling works well on the X86 and PowerPC targets. Currently - only Linux and Darwin targets are supported (both 32 and 64 bit).</li> -</ul> - -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a> -</div> - -<div class="doc_text"> -<ul> -<li>Fortran support generally works, but there are still several unresolved bugs - in Bugzilla. Please see the tools/gfortran component for details.</li> -</ul> -</div> - -<!-- ======================================================================= --> -<div class="doc_subsection"> - <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a> -</div> - -<div class="doc_text"> -The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature -technology, and problems should be expected. -<ul> -<li>The Ada front-end currently only builds on X86-32. This is mainly due -to lack of trampoline support (pointers to nested functions) on other platforms. -However, it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a> -which does support trampolines.</li> -<li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>. -This is due to lack of LLVM support for <tt>setjmp</tt>/<tt>longjmp</tt> style -exception handling, which is used internally by the compiler. -Workaround: configure with --disable-bootstrap.</li> -<li>The c380004, <a href="http://llvm.org/PR2010">c393010</a> -and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail -(c380004 also fails with gcc-4.2 mainline). -If the compiler is built with checks disabled then <a href="http://llvm.org/PR2010">c393010</a> -causes the compiler to go into an infinite loop, using up all system memory.</li> -<li>Some GCC specific Ada tests continue to crash the compiler.</li> -<li>The -E binder option (exception backtraces) -<a href="http://llvm.org/PR1982">does not work</a> and will result in programs -crashing if an exception is raised. Workaround: do not use -E.</li> -<li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start -or finish at a non-byte offset</a> in a record. Workaround: do not pack records -or use representation clauses that result in a field of a non-discrete type -starting or finishing in the middle of a byte.</li> -<li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers -'main' as generated by the Ada binder to be invalid</a>. -Workaround: hand edit the file to use pointers for <tt>argv</tt> and -<tt>envp</tt> rather than integers.</li> -<li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is -ignored</a>.</li> -</ul> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="additionalinfo">Additional Information</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p>A wide variety of additional information is available on the <a -href="http://llvm.org">LLVM web page</a>, in particular in the <a -href="http://llvm.org/docs/">documentation</a> section. The web page also -contains versions of the API documentation which is up-to-date with the -Subversion version of the source code. -You can access versions of these documents specific to this release by going -into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p> - -<p>If you have any questions or comments about LLVM, please feel free to contact -us via the <a href="http://llvm.org/docs/#maillist"> mailing -lists</a>.</p> - -</div> - -<!-- *********************************************************************** --> - -<hr> -<address> - <a href="http://jigsaw.w3.org/css-validator/check/referer"><img - src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a> - <a href="http://validator.w3.org/check/referer"><img - src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a> - - <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br> - Last modified: $Date: 2009-07-02 18:48:38 +0200 (Thu, 02 Jul 2009) $ -</address> - -</body> -</html> diff --git a/docs/tutorial/JITTutorial1.html b/docs/tutorial/JITTutorial1.html deleted file mode 100644 index 3b7b8de..0000000 --- a/docs/tutorial/JITTutorial1.html +++ /dev/null @@ -1,207 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" - "http://www.w3.org/TR/html4/strict.dtd"> - -<html> -<head> - <title>LLVM Tutorial 1: A First Function</title> - <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> - <meta name="author" content="Owen Anderson"> - <meta name="description" - content="LLVM Tutorial 1: A First Function."> - <link rel="stylesheet" href="../llvm.css" type="text/css"> -</head> - -<body> - -<div class="doc_title"> LLVM Tutorial 1: A First Function </div> - -<div class="doc_author"> - <p>Written by <a href="mailto:owen@apple.com">Owen Anderson</a></p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"><a name="intro">A First Function</a></div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p>For starters, let's consider a relatively straightforward function that takes three integer parameters and returns an arithmetic combination of them. This is nice and simple, especially since it involves no control flow:</p> - -<div class="doc_code"> -<pre> -int mul_add(int x, int y, int z) { - return x * y + z; -} -</pre> -</div> - -<p>As a preview, the LLVM IR we’re going to end up generating for this function will look like:</p> - -<div class="doc_code"> -<pre> -define i32 @mul_add(i32 %x, i32 %y, i32 %z) { -entry: - %tmp = mul i32 %x, %y - %tmp2 = add i32 %tmp, %z - ret i32 %tmp2 -} -</pre> -</div> - -<p>If you're unsure what the above code says, skim through the <a href="../LangRef.html">LLVM Language Reference Manual</a> and convince yourself that the above LLVM IR is actually equivalent to the original function. Once you’re satisfied with that, let's move on to actually generating it programmatically!</p> - -<p>Of course, before we can start, we need to <code>#include</code> the appropriate LLVM header files:</p> - -<div class="doc_code"> -<pre> -#include "llvm/Module.h" -#include "llvm/Function.h" -#include "llvm/PassManager.h" -#include "llvm/CallingConv.h" -#include "llvm/Analysis/Verifier.h" -#include "llvm/Assembly/PrintModulePass.h" -#include "llvm/Support/IRBuilder.h" -#include "llvm/Support/raw_ostream.h" -</pre> -</div> - -<p>Now, let's get started on our real program. Here's what our basic <code>main()</code> will look like:</p> - -<div class="doc_code"> -<pre> -using namespace llvm; - -Module* makeLLVMModule(); - -int main(int argc, char**argv) { - Module* Mod = makeLLVMModule(); - - verifyModule(*Mod, PrintMessageAction); - - PassManager PM; - PM.add(createPrintModulePass(&outs())); - PM.run(*Mod); - - delete Mod; - return 0; -} -</pre> -</div> - -<p>The first segment is pretty simple: it creates an LLVM “module.” In LLVM, a module represents a single unit of code that is to be processed together. A module contains things like global variables, function declarations, and implementations. Here we’ve declared a <code>makeLLVMModule()</code> function to do the real work of creating the module. Don’t worry, we’ll be looking at that one next!</p> - -<p>The second segment runs the LLVM module verifier on our newly created module. While this probably isn’t really necessary for a simple module like this one, it's always a good idea, especially if you’re generating LLVM IR based on some input. The verifier will print an error message if your LLVM module is malformed in any way.</p> - -<p>Finally, we instantiate an LLVM <code>PassManager</code> and run -the <code>PrintModulePass</code> on our module. LLVM uses an explicit pass -infrastructure to manage optimizations and various other things. -A <code>PassManager</code>, as should be obvious from its name, manages passes: -it is responsible for scheduling them, invoking them, and ensuring the proper -disposal after we’re done with them. For this example, we’re just using a -trivial pass that prints out our module in textual form.</p> - -<p>Now onto the interesting part: creating and populating a module. Here's the -first chunk of our <code>makeLLVMModule()</code>:</p> - -<div class="doc_code"> -<pre> -Module* makeLLVMModule() { - // Module Construction - Module* mod = new Module("test", getGlobalContext()); -</pre> -</div> - -<p>Exciting, isn’t it!? All we’re doing here is instantiating a module and giving it a name. The name isn’t particularly important unless you’re going to be dealing with multiple modules at once.</p> - -<div class="doc_code"> -<pre> - Constant* c = mod->getOrInsertFunction("mul_add", - /*ret type*/ IntegerType::get(32), - /*args*/ IntegerType::get(32), - IntegerType::get(32), - IntegerType::get(32), - /*varargs terminated with null*/ NULL); - - Function* mul_add = cast<Function>(c); - mul_add->setCallingConv(CallingConv::C); -</pre> -</div> - -<p>We construct our <code>Function</code> by calling <code>getOrInsertFunction()</code> on our module, passing in the name, return type, and argument types of the function. In the case of our <code>mul_add</code> function, that means one 32-bit integer for the return value and three 32-bit integers for the arguments.</p> - -<p>You'll notice that <code>getOrInsertFunction()</code> doesn't actually return a <code>Function*</code>. This is because <code>getOrInsertFunction()</code> will return a cast of the existing function if the function already existed with a different prototype. Since we know that there's not already a <code>mul_add</code> function, we can safely just cast <code>c</code> to a <code>Function*</code>. - -<p>In addition, we set the calling convention for our new function to be the C -calling convention. This isn’t strictly necessary, but it ensures that our new -function will interoperate properly with C code, which is a good thing.</p> - -<div class="doc_code"> -<pre> - Function::arg_iterator args = mul_add->arg_begin(); - Value* x = args++; - x->setName("x"); - Value* y = args++; - y->setName("y"); - Value* z = args++; - z->setName("z"); -</pre> -</div> - -<p>While we’re setting up our function, let's also give names to the parameters. This also isn’t strictly necessary (LLVM will generate names for them if you don’t specify them), but it’ll make looking at our output somewhat more pleasant. To name the parameters, we iterate over the arguments of our function and call <code>setName()</code> on them. We’ll also keep the pointer to <code>x</code>, <code>y</code>, and <code>z</code> around, since we’ll need them when we get around to creating instructions.</p> - -<p>Great! We have a function now. But what good is a function if it has no body? Before we start working on a body for our new function, we need to recall some details of the LLVM IR. The IR, being an abstract assembly language, represents control flow using jumps (we call them branches), both conditional and unconditional. The straight-line sequences of code between branches are called basic blocks, or just blocks. To create a body for our function, we fill it with blocks:</p> - -<div class="doc_code"> -<pre> - BasicBlock* block = BasicBlock::Create(getGlobalContext(), "entry", mul_add); - IRBuilder<> builder(block); -</pre> -</div> - -<p>We create a new basic block, as you might expect, by calling its constructor. All we need to tell it is its name and the function to which it belongs. In addition, we’re creating an <code>IRBuilder</code> object, which is a convenience interface for creating instructions and appending them to the end of a block. Instructions can be created through their constructors as well, but some of their interfaces are quite complicated. Unless you need a lot of control, using <code>IRBuilder</code> will make your life simpler.</p> - -<div class="doc_code"> -<pre> - Value* tmp = builder.CreateBinOp(Instruction::Mul, - x, y, "tmp"); - Value* tmp2 = builder.CreateBinOp(Instruction::Add, - tmp, z, "tmp2"); - - builder.CreateRet(tmp2); - - return mod; -} -</pre> -</div> - -<p>The final step in creating our function is to create the instructions that make it up. Our <code>mul_add</code> function is composed of just three instructions: a multiply, an add, and a return. <code>IRBuilder</code> gives us a simple interface for constructing these instructions and appending them to the “entry” block. Each of the calls to <code>IRBuilder</code> returns a <code>Value*</code> that represents the value yielded by the instruction. You’ll also notice that, above, <code>x</code>, <code>y</code>, and <code>z</code> are also <code>Value*</code>'s, so it's clear that instructions operate on <code>Value*</code>'s.</p> - -<p>And that's it! Now you can compile and run your code, and get a wonderful textual print out of the LLVM IR we saw at the beginning. To compile, use the following command line as a guide:</p> - -<div class="doc_code"> -<pre> -# c++ -g tut1.cpp `llvm-config --cxxflags --ldflags --libs core` -o tut1 -# ./tut1 -</pre> -</div> - -<p>The <code>llvm-config</code> utility is used to obtain the necessary GCC-compatible compiler flags for linking with LLVM. For this example, we only need the 'core' library. We'll use others once we start adding optimizers and the JIT engine.</p> - -<a href="JITTutorial2.html">Next: A More Complicated Function</a> -</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="mailto:owen@apple.com">Owen Anderson</a><br> - <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> - Last modified: $Date: 2009-07-21 11:05:13 -0700 (Tue, 21 Jul 2009) $ -</address> - -</body> -</html> diff --git a/docs/tutorial/JITTutorial2-1.png b/docs/tutorial/JITTutorial2-1.png Binary files differdeleted file mode 100644 index eb21695..0000000 --- a/docs/tutorial/JITTutorial2-1.png +++ /dev/null diff --git a/docs/tutorial/JITTutorial2.html b/docs/tutorial/JITTutorial2.html deleted file mode 100644 index 504d965..0000000 --- a/docs/tutorial/JITTutorial2.html +++ /dev/null @@ -1,200 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" - "http://www.w3.org/TR/html4/strict.dtd"> - -<html> -<head> - <title>LLVM Tutorial 2: A More Complicated Function</title> - <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> - <meta name="author" content="Owen Anderson"> - <meta name="description" - content="LLVM Tutorial 2: A More Complicated Function."> - <link rel="stylesheet" href="../llvm.css" type="text/css"> -</head> - -<body> - -<div class="doc_title"> LLVM Tutorial 2: A More Complicated Function </div> - -<div class="doc_author"> - <p>Written by <a href="mailto:owen@apple.com">Owen Anderson</a></p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"><a name="intro">A First Function</a></div> -<!-- *********************************************************************** --> - -<div class="doc_text"> - -<p>Now that we understand the basics of creating functions in LLVM, let's move on to a more complicated example: something with control flow. As an example, let's consider Euclid's Greatest Common Denominator (GCD) algorithm:</p> - -<div class="doc_code"> -<pre> -unsigned gcd(unsigned x, unsigned y) { - if(x == y) { - return x; - } else if(x < y) { - return gcd(x, y - x); - } else { - return gcd(x - y, y); - } -} -</pre> -</div> - -<p>With this example, we'll learn how to create functions with multiple blocks and control flow, and how to make function calls within your LLVM code. For starters, consider the diagram below.</p> - -<div style="text-align: center;"><img src="JITTutorial2-1.png" alt="GCD CFG" width="60%"></div> - -<p>This is a graphical representation of a program in LLVM IR. It places each basic block on a node of a graph and uses directed edges to indicate flow control. These blocks will be serialized when written to a text or bitcode file, but it is often useful conceptually to think of them as a graph. Again, if you are unsure about the code in the diagram, you should skim through the <a href="../LangRef.html">LLVM Language Reference Manual</a> and convince yourself that it is, in fact, the GCD algorithm.</p> - -<p>The first part of our code is practically the same as from the first tutorial. The same basic setup is required: creating a module, verifying it, and running the <code>PrintModulePass</code> on it. Even the first segment of <code>makeLLVMModule()</code> looks essentially the same, except that <code>gcd</code> takes one fewer parameter than <code>mul_add</code>.</p> - -<div class="doc_code"> -<pre> -#include "llvm/Module.h" -#include "llvm/Function.h" -#include "llvm/PassManager.h" -#include "llvm/Analysis/Verifier.h" -#include "llvm/Assembly/PrintModulePass.h" -#include "llvm/Support/IRBuilder.h" -#include "llvm/Support/raw_ostream.h" - -using namespace llvm; - -Module* makeLLVMModule(); - -int main(int argc, char**argv) { - Module* Mod = makeLLVMModule(); - - verifyModule(*Mod, PrintMessageAction); - - PassManager PM; - PM.add(createPrintModulePass(&outs())); - PM.run(*Mod); - - delete Mod; - return 0; -} - -Module* makeLLVMModule() { - Module* mod = new Module("tut2"); - - Constant* c = mod->getOrInsertFunction("gcd", - IntegerType::get(32), - IntegerType::get(32), - IntegerType::get(32), - NULL); - Function* gcd = cast<Function>(c); - - Function::arg_iterator args = gcd->arg_begin(); - Value* x = args++; - x->setName("x"); - Value* y = args++; - y->setName("y"); -</pre> -</div> - -<p>Here, however, is where our code begins to diverge from the first tutorial. Because <code>gcd</code> has control flow, it is composed of multiple blocks interconnected by branching (<code>br</code>) instructions. For those familiar with assembly language, a block is similar to a labeled set of instructions. For those not familiar with assembly language, a block is basically a set of instructions that can be branched to and is executed linearly until the block is terminated by one of a small number of control flow instructions, such as <code>br</code> or <code>ret</code>.</p> - -<p>Blocks correspond to the nodes in the diagram we looked at in the beginning of this tutorial. From the diagram, we can see that this function contains five blocks, so we'll go ahead and create them. Note that we're making use of LLVM's automatic name uniquing in this code sample, since we're giving two blocks the same name.</p> - -<div class="doc_code"> -<pre> - BasicBlock* entry = BasicBlock::Create(getGlobalContext(), ("entry", gcd); - BasicBlock* ret = BasicBlock::Create(getGlobalContext(), ("return", gcd); - BasicBlock* cond_false = BasicBlock::Create(getGlobalContext(), ("cond_false", gcd); - BasicBlock* cond_true = BasicBlock::Create(getGlobalContext(), ("cond_true", gcd); - BasicBlock* cond_false_2 = BasicBlock::Create(getGlobalContext(), ("cond_false", gcd); -</pre> -</div> - -<p>Now we're ready to begin generating code! We'll start with the <code>entry</code> block. This block corresponds to the top-level if-statement in the original C code, so we need to compare <code>x</code> and <code>y</code>. To achieve this, we perform an explicit comparison using <code>ICmpEQ</code>. <code>ICmpEQ</code> stands for an <em>integer comparison for equality</em> and returns a 1-bit integer result. This 1-bit result is then used as the input to a conditional branch, with <code>ret</code> as the <code>true</code> and <code>cond_false</code> as the <code>false</code> case.</p> - -<div class="doc_code"> -<pre> - IRBuilder<> builder(entry); - Value* xEqualsY = builder.CreateICmpEQ(x, y, "tmp"); - builder.CreateCondBr(xEqualsY, ret, cond_false); -</pre> -</div> - -<p>Our next block, <code>ret</code>, is pretty simple: it just returns the value of <code>x</code>. Recall that this block is only reached if <code>x == y</code>, so this is the correct behavior. Notice that instead of creating a new <code>IRBuilder</code> for each block, we can use <code>SetInsertPoint</code> to retarget our existing one. This saves on construction and memory allocation costs.</p> - -<div class="doc_code"> -<pre> - builder.SetInsertPoint(ret); - builder.CreateRet(x); -</pre> -</div> - -<p><code>cond_false</code> is a more interesting block: we now know that <code>x -!= y</code>, so we must branch again to determine which of <code>x</code> -and <code>y</code> is larger. This is achieved using the <code>ICmpULT</code> -instruction, which stands for <em>integer comparison for unsigned -less-than</em>. In LLVM, integer types do not carry sign; a 32-bit integer -pseudo-register can be interpreted as signed or unsigned without casting. -Whether a signed or unsigned interpretation is desired is specified in the -instruction. This is why several instructions in the LLVM IR, such as integer -less-than, include a specifier for signed or unsigned.</p> - -<p>Also note that we're again making use of LLVM's automatic name uniquing, this time at a register level. We've deliberately chosen to name every instruction "tmp" to illustrate that LLVM will give them all unique names without getting confused.</p> - -<div class="doc_code"> -<pre> - builder.SetInsertPoint(cond_false); - Value* xLessThanY = builder.CreateICmpULT(x, y, "tmp"); - builder.CreateCondBr(xLessThanY, cond_true, cond_false_2); -</pre> -</div> - -<p>Our last two blocks are quite similar; they're both recursive calls to <code>gcd</code> with different parameters. To create a call instruction, we have to create a <code>vector</code> (or any other container with <code>InputInterator</code>s) to hold the arguments. We then pass in the beginning and ending iterators for this vector.</p> - -<div class="doc_code"> -<pre> - builder.SetInsertPoint(cond_true); - Value* yMinusX = builder.CreateSub(y, x, "tmp"); - std::vector<Value*> args1; - args1.push_back(x); - args1.push_back(yMinusX); - Value* recur_1 = builder.CreateCall(gcd, args1.begin(), args1.end(), "tmp"); - builder.CreateRet(recur_1); - - builder.SetInsertPoint(cond_false_2); - Value* xMinusY = builder.CreateSub(x, y, "tmp"); - std::vector<Value*> args2; - args2.push_back(xMinusY); - args2.push_back(y); - Value* recur_2 = builder.CreateCall(gcd, args2.begin(), args2.end(), "tmp"); - builder.CreateRet(recur_2); - - return mod; -} -</pre> -</div> - -<p>And that's it! You can compile and execute your code in the same way as before, by doing:</p> - -<div class="doc_code"> -<pre> -# c++ -g tut2.cpp `llvm-config --cxxflags --ldflags --libs core` -o tut2 -# ./tut2 -</pre> -</div> - -</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="mailto:owen@apple.com">Owen Anderson</a><br> - <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> - Last modified: $Date: 2007-10-17 11:05:13 -0700 (Wed, 17 Oct 2007) $ -</address> - -</body> -</html> |
