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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 1.5 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 1.5 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.cs.uiuc.edu">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 1.5. 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.cs.uiuc.edu/releases/1.5/">LLVM 1.5 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.cs.uiuc.edu">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.cs.uiuc.edu/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 sixth public release of the LLVM Compiler Infrastructure.</p>
<p> At this time, LLVM is known to correctly compile a wide range of C and C++
programs, including the SPEC CPU95 & 2000 suite. It includes bug fixes for
those problems found since the 1.4 release and a large number of new features
and enhancements, described below.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="newfeatures">New Features in LLVM 1.5</a>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection">New Native Code Generators</div>
<div class="doc_text">
<p>
This release includes new native code generators for <a
href="#alpha-be">Alpha</a>, <a href="#ia64-be">IA-64</a>, and SPARC-V8 (32-bit
SPARC). These code generators are still beta quality, but are progressing
rapidly.
</p>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection">New Instruction Selector Framework</div>
<div class="doc_text">
<p>This release includes a <a href="CodeGenerator.html#instselect">new framework
for building instruction selectors</a>, which has long been the hardest part of
building a new LLVM target. This framework handles a lot of the mundane (but
easy to get wrong) details of writing the instruction selector, such as
generating efficient code for <a
href="LangRef.html#i_getelementptr">getelementptr</a> instructions, promoting
small integer types to larger types (e.g. for RISC targets with one size of
integer registers), expanding 64-bit integer operations for 32-bit hosts, etc.
Currently, the X86, PowerPC, Alpha, and IA-64 backends use this framework. The
SPARC backends will be migrated when time permits.
</p>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection">New Support For Custom Calling Convetions</div>
<div class="doc_text">
<p>LLVM 1.5 adds supports for <a href="LangRef.html#callingconv">custom and
target-specific calling conventions</a>. Traditionally, the LLVM code
generators match the native C calling conventions for a target. This is
important for compatibility, but is not very flexible. This release allows
custom calling conventions to be established for functions, and defines three
target-independent conventions (C call, fast call, and cold call) which may be
supported by code generators. When possible, the LLVM optimizer promotes C
functions to use the "fastcc" convention, allowing the use of more efficient
calling sequences (e.g., parameters are passed in registers in the X86 target).
</p>
<p>Targets may now also define target-specific calling conventions, allowing
LLVM to fully support calling convention altering options (e.g. GCC's
<tt>-mregparm</tt> flag) and well-defined target conventions (e.g. stdcall and
fastcall on X86).</p>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection">New Support for "Proper Tail Calls"</div>
<div class="doc_text">
<p>The release now includes support for <a
href="http://doi.acm.org/10.1145/277650.277719">proper tail calls</a>, as
required to implement languages like Scheme. Tail calls make use of two
features: custom calling conventions (described above), which allow the code
generator to emit code for the caller to deallocate its own stack when it
returns. The second feature is a flag on the <a href="LangRef.html#i_call">call
instruction</a>, which indicates that the callee does not access the callers
stack frame (indicating that it is acceptable to deallocate the caller stack
before invoking the callee). LLVM proper tail calls run on the system stack (as
do normal calls), supports indirect tail calls, tail calls with arbitrary
numbers of arguments, tail calls where the callee requires more argument space
than the caller, etc. The only case not supported are varargs calls, but that
could be added if desired.
</p>
<p>In order for a front-end to get guaranteed tail call, it must mark functions
as "fastcc", mark calls with the 'tail' marker, and follow the call with a
return of the called value (or void). The optimizer and code generator attempt
to handle more general cases, but the simple case will always work if the code
generator supports tail calls. Here is a simple example:</p>
<p><pre>
fastcc int %bar(int %X, int(double, int)* %FP) { ;<i> fastcc</i>
%Y = tail call fastcc int %FP(double 0.0, int %X) ;<i> tail, fastcc</i>
ret int %Y
}
</pre></p>
<p>In LLVM 1.5, the X86 code generator is the only target that has been enhanced
to support proper tail calls (other targets will be enhanced in future).
Further, because this support was added very close to the release, it is
disabled by default. Pass <tt>-enable-x86-fastcc</tt> to llc to enable it (this
will be enabled by default in the next release). The example above compiles to:
</p>
<p><pre>
bar:
sub ESP, 8 # Callee uses more space than the caller
mov ECX, DWORD PTR [ESP + 8] # Get the old return address
mov DWORD PTR [ESP + 4], 0 # First half of 0.0
mov DWORD PTR [ESP + 8], 0 # Second half of 0.0
mov DWORD PTR [ESP], ECX # Put the return address where it belongs
jmp EDX # Tail call "FP"
</pre></p>
<p>
With fastcc on X86, the first two integer arguments are passed in EAX/EDX, the
callee pops its arguments off the stack, and the argument area is always a
multiple of 8 bytes in size.
</p>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection">Other New Features</div>
<div class="doc_text">
<ol>
<li>LLVM now includes an <a href="http://llvm.cs.uiuc.edu/PR415">
Interprocedural Sparse Conditional Constant Propagation</a> pass, named
-ipsccp, which is run by default at link-time.</li>
<li>LLVM 1.5 is now about 15% faster than LLVM 1.4 and its core data
structures use about 30% less memory.</li>
<li>Support for Microsoft Visual Studio is improved, and <a
href="GettingStartedVS.html">now documented</a>.</li>
<li><a href="GettingStarted.html#config">Configuring LLVM to build a subset
of the available targets</a> is now implemented, via the
<tt>--enable-targets=</tt> option.</li>
<li>LLVM can now create native shared libraries with '<tt>llvm-gcc ...
-shared -Wl,-native</tt>' (or with <tt>-Wl,-native-cbe</tt>).</li>
<li>LLVM now supports a new "<a href="LangRef.html#i_prefetch">llvm.prefetch
</a>" intrinsic, and llvm-gcc now supports __builtin_prefetch.
<li>LLVM now supports intrinsics for <a href="LangRef.html#int_count">bit
counting</a> and llvm-gcc now implements the GCC
<tt>__builtin_popcount</tt>, <tt>__builtin_ctz</tt>, and
<tt>__builtin_clz</tt> builtins.</li>
<li>LLVM now builds on HP-UX with the HP aCC Compiler.</li>
<li>The LLVM X86 backend can now emit Cygwin-compatible .s files.</li>
<li>LLVM now includes workarounds in the code generator generator which
reduces the likelyhood of <a href="http://llvm.cs.uiuc.edu/PR448">GCC
hitting swap during optimized builds</a>.</li>
</ol>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="codequality">Code Quality Improvements in LLVM 1.5</a>
</div>
<div class="doc_text">
<ol>
<li>The -globalopt pass now promotes non-address-taken static globals that are
only accessed in main to SSA registers.</li>
<li>The new -simplify-libcalls pass improves code generated for well-known
library calls. The pass optimizes calls to many of the string, memory, and
standard I/O functions (e.g. replace the calls with simpler/faster calls) when
possible, given information known statically about the arguments to the call.
</li>
&l
|
