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|
<!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 2.2 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 2.2 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
<li><a href="#whatsnew">What's New?</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><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 2.2. Here we describe the status of LLVM, including
major improvements from the previous release and any 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 releases, please see the
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="whatsnew">What's New?</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>This is the thirteenth public release of the LLVM Compiler Infrastructure.
It includes many features and refinements from LLVM 2.1.</p>
</div>
<!-- Unfinished features in 2.2:
Index Set Splitting not enabled by default
Machine LICM
Machine Sinking
LegalizeDAGTypes
-->
<!--=========================================================================-->
<div class="doc_subsection">
<a name="deprecation">Deprecated features in LLVM 2.2</a>
</div>
<div class="doc_text">
<p>This is the last LLVM release to support llvm-gcc 4.0, llvm-upgrade, and
llvmc in its current form. llvm-gcc 4.0 has been replaced with llvm-gcc 4.2.
llvm-upgrade is useful for upgrading llvm 1.9 files to llvm 2.x syntax, but you
can always use an old release to do this. llvmc is currently mostly useless in
llvm 2.2, and will be redesigned or removed in llvm 2.3.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="frontends">llvm-gcc 4.0, llvm-gcc 4.2, and clang</a>
</div>
<div class="doc_text">
<p>LLVM 2.2 fully supports both the llvm-gcc 4.0 and llvm-gcc 4.2 front-ends (in
LLVM 2.1, llvm-gcc 4.2 was beta). Since LLVM 2.1, the llvm-gcc 4.2 front-end
has made leaps and bounds and is now at least as good as 4.0 in virtually every
area, and is better in several areas (for example, exception handling
correctness, support for Ada and Fortran, better ABI compatibility, etc). We
strongly recommend that you
migrate from llvm-gcc 4.0 to llvm-gcc 4.2 in this release cycle because
<b>LLVM 2.2 is the last release that will support llvm-gcc 4.0</b>: LLVM 2.3
will only support the llvm-gcc 4.2 front-end.</p>
<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. Currently, its C and Objective-C support is maturing
nicely, and it has advanced source-to-source analysis and transformation
capabilities. If you are interested in building source-level tools for C and
Objective-C (and eventually C++), you should take a look. However, note that
clang is not an official part of the LLVM 2.2 release. If you are interested in
this project, please see its <a href="http://clang.llvm.org/">web site</a>.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="majorfeatures">Major New Features</a>
</div>
<div class="doc_text">
<p>LLVM 2.2 includes several major new capabilities:</p>
<ul>
<li>A research team led by Scott Michel in the Computer Systems Research
Department at The Aerospace Corporation contributed the CellSPU backend, which
generates code for the vector coprocessors on the Sony/Toshiba/IBM Cell BE
processor. llvm-gcc 4.2 supports CellSPU as a 'configure' target and progress
is being made so that libgcc.a compiles cleanly. Notable pieces still in
development include full 64-bit integer and full double precision floating
point support.</li>
<li>Anton and Duncan significantly improved llvm-gcc 4.2 support for the GCC Ada
(GNAT) and Fortran (gfortran) front-ends. These front-ends should still be considered
experimental however: see the <a href="#knownproblems">list of known problems</a>.
The release binaries do not contain either front-end: they need to be built from
source (the Ada front-end only builds on x86-32 linux).</li>
<li>Dale contributed full support for long double on x86/x86-64 (where it is 80
bits) and on Darwin PPC/PPC64 (where it is 128 bits). In previous LLVM
releases, llvm-gcc silently mapped long double to double.</li>
<li>Gordon Henriksen rewrote most of the <a href="GarbageCollection.html"
>Accurate Garbage Collection</a> code in the code generator, making the
generated code more efficient and adding support for the OCaml garbage collector
metadata format.</li>
<li>Christopher Lamb contributed support for multiple address spaces in LLVM
IR. This is useful for supporting targets that have 'near' vs 'far' pointers,
'RAM' vs 'ROM' pointers, or that have non-local memory that can be accessed with
special instructions.</li>
<li>LLVM now includes a new set of detailed <a
href="tutorial/index.html">tutorials</a>, which explain how to implement a
language with LLVM and shows how to use several important APIs.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="coreimprovements">LLVM Core Improvements</a>
</div>
<div class="doc_text">
<p>New features include:
</p>
<ul>
<li>Gordon contributed support for C and OCaml Bindings for the basic LLVM IR
construction routines as well as several other auxiliary APIs.</li>
<li>Anton added readnone/readonly attributes for modeling function side effects.
Duncan hooked up GCC's pure/const attributes to them and enhanced mod/ref
analysis to use them.</li>
<li>Devang added LLVMFoldingBuilder, a version of LLVMBuilder that implicitly
simplifies the code as it is constructed.</li>
<li>Ted Kremenek added a framework for generic object serialization to bitcode
files. This support is only used by clang right now for ASTs but is extensible
and could be used for serializing arbitrary other data into bitcode files.</li>
<li>Duncan improved TargetData to distinguish between the size/alignment of a
type in a register, in memory according to the platform ABI, and in memory when
we have a choice.</li>
<li>Reid moved parameter attributes off of FunctionType and onto functions
and calls. This makes it much easier to add attributes to a function in a
transformation pass.</li>
<li>Dan Gohman added support for vector sin, cos, and pow intrinsics.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="codegen">Code Generator Improvements</a>
</div>
<div class="doc_text">
<p>We 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>Owen refactored the existing LLVM dominator and loop information code to
allow it work on the machine code representation. He contributed support for
dominator and loop information on machine code and merged the code for forward
and backward dominator computation.</li>
<li>Dan added support for emitting debug information with .file and .loc
directives on platforms that support it, instead of emitting large tables in the .s
file.</li>
<li>Evan extended the DAG scheduler to model physical register dependencies
explicitly and have the BURR scheduler pick a correct schedule based on the
dependencies. This reduces our use of the 'flag' operand hack.</li>
<li>Evan added initial support for register coalescing of subregister
references.</li>
<li>Rafael Espindola implemented initial support for a new 'byval' attribute,
which allows more efficient by-value argument passing in the LLVM IR. Evan
finished support for it and enabled it in the X86 (32- and 64-bit) and C
backends.</li>
<li>The LLVM TargetInstrInfo class can now answer queries about the mod/ref and
side-effect behavior of MachineInstr's. This information is inferred
automatically by TableGen from .td files for all instructions with
patterns.</li>
<li>Evan implemented simple live interval splitting on basic block boundaries.
This allows the register allocator to be more successful at keeping values in
registers in some parts of a value's live range, even if they need to be spilled
in some other block.</li>
<li>The new MachineRegisterInfo.h class provides support for efficiently
iterating over all defs/uses of a register, and this information is
automatically kept up-to-date. This support is similar to the use_iterator in
the LLVM IR level.</li>
<li>The MachineInstr, MachineOperand and TargetInstrDesc classes are simpler,
more consistent, and better documented.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="optimizer">Optimizer Improvements</a>
</div>
<div class="doc_text">
<p>In addition to a huge array of bug fixes and minor performance tweaks, the
LLVM 2.2 optimizers support a few major enhancements:</p>
<ul>
<li>Daniel Berlin and Curtis Dunham rewrote Andersen's alias analysis to be
several orders of magnitude faster, and implemented Offline Variable
Substitution and Lazy Cycle Detection. Note that Andersen's is not enabled in
llvm-gcc by default, but can be accessed through 'opt'.</li>
<li>Dan Gohman contributed several enhancements to Loop Strength Reduction (LSR)
to make it more aggressive with SSE intrinsics and when induction variables are
used by non-memory instructions.</li>
<li>Evan added support for simple exit value substitution to LSR.</li>
<li>Evan enhanced LSR to support induction variable reuse when the induction
variables have different widths.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
|
