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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 1.6 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 1.6 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 1.6. Here we describe the status of LLVM, including any
known problems and major improvements from the previous release. The most
up-to-date version of this document can be found on the <a
href="http://llvm.org/releases/1.6/">LLVM 1.6 web site</a>. If you are
not reading this on the LLVM web pages, you should probably go there because
this document may be updated after the release.</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 CVS 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 the current or previous releases, 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 seventh public release of the LLVM Compiler Infrastructure. This
release incorporates a large number of enhancements and additions (primarily in
the code generator), which combine to improve the quality of the code generated
by LLVM by up to 30% in some cases. This release is also the first release to
have first-class support for Mac OS/X: all of the major bugs have been shaken
out and it is now as well supported as Linux on X86.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="newfeatures">New Features in LLVM 1.6</a>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="iselgen">Instruction Selector
Generation from Target Description</a></div>
<div class="doc_text">
<p>LLVM now includes support for auto-generating large portions of the
instruction selectors from target descriptions. This allows us to
write patterns in the target .td file, instead of writing lots of
nasty C++ code. Most of the PowerPC instruction selector is now
generated from the PowerPC target description files and other targets
are adding support that will be live for LLVM 1.7.</p>
<p>For example, here are some patterns used by the PowerPC backend. A
floating-point multiply then subtract instruction (FMSUBS):</p>
<div class="doc_code"><p>
<tt>(set F4RC:$FRT, (fsub (fmul F4RC:$FRA, F4RC:$FRC), F4RC:$FRB))</tt>
</p></div>
<p>Exclusive-or by 16-bit immediate (XORI):</p>
<div class="doc_code"><p>
<tt>(set GPRC:$dst, (xor GPRC:$src1, immZExt16:$src2))</tt>
</p></div>
<p>Exclusive-or by 16-bit immediate shifted right 16-bits (XORIS):</p>
<div class="doc_code"><p>
<tt>(set GPRC:$dst, (xor GPRC:$src1, imm16Shifted:$src2))</tt>
</p></div>
<p>With these definitions, we teach the code generator how to combine these two
instructions to xor an abitrary 32-bit immediate with the following
definition. The first line specifies what to match (a xor with an arbitrary
immediate) the second line specifies what to produce:</p>
<div class="doc_code"><p>
<pre>def : Pat<(xor GPRC:$in, imm:$imm),
(XORIS (XORI GPRC:$in, (LO16 imm:$imm)), (HI16 imm:$imm))>;
</pre>
</p></div>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="sched">Instruction Scheduling
Support</a></div>
<div class="doc_text">
<p>Instruction selectors using the refined <a
href="CodeGenerator.html#instselect">instruction selection framework</a> can now
use a simple pre-pass scheduler included with LLVM 1.6. This scheduler is
currently simple (cannot be configured much by the targets), but will be
extended in the future.</p>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="subtarget">Code Generator Subtarget
Support</a></div>
<div class="doc_text">
<p>It is now straight-forward to parameterize a target implementation, and
provide a mapping from CPU names to sets of target parameters. LLC now supports
a <tt>-mcpu=cpu</tt> option that lets you choose a subtarget by CPU name: use
"<tt>llvm-as < /dev/null | llc -march=XXX -mcpu=help</tt>" to get a list of
supported CPUs for target "XXX". It also provides a
<tt>-mattr=+attr1,-attr2</tt> option that can be used to control individual
features of a target (the previous command will list available features as
well).</p>
<p>This functionality is nice when you want tell LLC something like "compile to
code that is specialized for the PowerPC G5, but doesn't use altivec code. In
this case, using "<tt>llc -march=ppc32 -mcpu=g5 -mattr=-altivec</tt>".</p>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="jitlock">Other New Features</a></div>
<div class="doc_text">
<ol>
<li>The JIT now uses mutexes to protect its internal data structures. This
allows multi-threaded programs to be run from the JIT or interpreter without
corruption of the internal data structures. See
<a href="http://llvm.org/PR418">PR418</a> and
<a href="http://llvm.org/PR540">PR540</a> for the details.
</li>
<li>LLVM on Win32 <a href="http://llvm.org/PR614">no longer requires sed,
flex, or bison when compiling with Visual C++</a>.</li>
<li>The llvm-test suite can now use the NAG Fortran to C compiler to compile
SPEC FP programs if available (allowing us to test all of SPEC'95 &
2000).</li>
<li>When bugpoint is grinding away and the user hits ctrl-C, it now
gracefully stops and gives what it has reduced so far, instead of
giving up completely. In addition, <a href="http://llvm.org/PR576">the JIT
debugging mode of bugpoint is much faster</a>.</li>
<li>LLVM now includes Xcode project files in the llvm/Xcode directory.</li>
<li>LLVM now supports Mac OS/X on Intel.</li>
<li>LLVM now builds cleanly with GCC 4.1.</li>
</ol>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="codequality">Code Quality Improvements in LLVM 1.6</a>
</div>
<div class="doc_text">
<ol>
<li>The <tt>-globalopt</tt> pass can now statically evaluate C++ static
constructors when they are simple enough. For example, it can
now statically initialize "<tt>struct X { int a; X() : a(4) {} } g;</tt>".
</li>
<li>The Loop Strength Reduction pass has been completely rewritten, is far
more aggressive, and is turned on by default in the RISC targets. On PPC,
we find that it often speeds up programs from 10-40% depending on the
program.</li>
<li>The code produced when exception handling is enabled is far more
efficient in some cases, particularly on Mac OS/X.</li>
</ol>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="codequality">Code Generator Improvements in LLVM 1.6</a>
</div>
<div class="doc_text">
<ol>
<li>The Alpha backend is substantially more stable and robust than in LLVM 1.5.
For example, it now fully supports varargs functions. The Alpha backend
also now features beta JIT support.</li>
<li>The code generator contains a new component, the DAG Combiner. This allows
us to optimize lowered code (e.g. after 64-bit operations have been lowered
to use 32-bit registers on 32-bit targets) and do fine-grained bit-twiddling
optimizations for the backend.</li>
<li>The SelectionDAG infrastructure is far more capable and mature, able to
handle many new target peculiarities in a target-independent way.</li>
<li>The default <a href="http://llvm.org/PR547">register allocator is now far
faster on some testcases</a>,
particularly on targets with a large number of registers (e.g. IA64
and PPC).</li>
</ol>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="bugfix">Significant Bugs Fixed in LLVM 1.6</a>
</div>
<div class="doc_text">
<ol>
<li>A vast number of bugs have been fixed in the PowerPC backend and in
llvm-gcc when configured for Mac OS/X (particularly relating to ABI
issues). For example:
<a href="http://llvm.org/PR603">PR449</a>,
<a href="http://llvm.org/PR594">PR594</a>,
<a
|
