<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>
+ <title>LLVM 2.1 Release Notes</title>
</head>
<body>
-<div class="doc_title">LLVM 1.5 Release Notes</div>
+<div class="doc_title">LLVM 2.1 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
</ol>
<div class="doc_author">
- <p>Written by the <a href="http://llvm.
cs.uiuc.edu">LLVM Team</a><p>
+ <p>Written by the <a href="http://llvm.
org">LLVM Team</a><p>
</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>
+infrastructure, release 2.1. 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.cs.uiuc.edu">main LLVM
+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.cs.uiuc.edu/releases/">releases page</a>.</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_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>
+<p>This is the twelfth public release of the LLVM Compiler Infrastructure.
+It includes many features and refinements from LLVM 2.0.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="newfeatures">New Features in LLVM 1.5</a>
+<a name="frontends">New Frontends</a>
</div>
-<!--_________________________________________________________________________-->
-<div class="doc_subsubsection"><a name="newcg">New Native Code
-Generators</a></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 <a
-href="#sparcv8">SPARC-V8</a> (32-bit SPARC). These code generators are still
-beta quality, but are progressing rapidly. The Alpha backend is implemented
-with an eye towards being compatible with the widely used SimpleScalar
-simulator.
-</p>
-</div>
-<!--_________________________________________________________________________-->
-<div class="doc_subsubsection"><a name="selectiondag">New Instruction
-Selector Framework</a></div>
+<p>LLVM 2.1 brings two new beta C front-ends. First, a new version of llvm-gcc
+based on GCC 4.2, innovatively called "llvm-gcc-4.2". This promises to bring
+FORTRAN and Ada support to LLVM as well as features like atomic builtins and
+OpenMP. None of these actually work yet, but don't let that stop you checking
+it out!</p>
+
+<p>Second, LLVM now includes its own native C and Objective-C front-end (C++ is
+in progress, but is not very far along) code named "<a
+href="http://clang.llvm.org/">clang</a>". This front-end has a number of great
+features, primarily aimed at source-level analysis and speeding up compile-time.
+At this point though, the LLVM Code Generator component is still very early in
+development, so it's mostly useful for people looking to build source-level
+analysis tools or source-to-source translators.</p>
-<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"><a name="customccs">New Support for Per-Function
-Calling Conventions</a></div>
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="optimizer">Optimizer Improvements</a>
+</div>
<div class="doc_text">
-<p>LLVM 1.5 adds supports for <a href="LangRef.html#callingconv">per-function
-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 (<a
-href="LangRef.html#callingconv">C call, fast call, and cold call</a>) 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>
+<p>Some of the most noticable feature improvements this release have been in the
+optimizer, speeding it up and making it more aggressive. For example:</p>
+
+<ul>
+
+<li>Owen Anderson wrote the new MemoryDependenceAnalysis pass, which provides
+ a lazy, caching layer on top of <a
+ href="AliasAnalysis.html">AliasAnalysis</a>. He then used it to rewrite
+ DeadStoreElimination which resulted in significantly better compile time in
+ common cases, </li>
+<li>Owen implemented the new GVN pass, which is also based on
+ MemoryDependenceAnalysis. This pass replaces GCSE/LoadVN in the standard
+ set of passes, providing more aggressive optimization at a some-what
+ improved compile-time cost.</li>
+<li>Owen implemented GVN-PRE, a partial redundancy elimination algorithm that
+ shares some details with the new GVN pass. It is still in need of compile
+ time tuning, and is not turned on by default.</li>
+<li>Devang merged ETForest and DomTree into a single easier to use data
+ structure. This makes it more obvious which datastructure to choose
+ (because there is only one) and makes the compiler more memory and time
+ efficient (less stuff to keep up-to-date).</li>
+<li>Nick Lewycky improved loop trip count analysis to handle many more common
+ cases.</li>
+
+</ul>
+
</div>
-<!--_________________________________________________________________________-->
-<div class="doc_subsubsection"><a name="tailcalls">New Support for
-Proper Tail Calls</a></div>
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="codegen">Code Generator Improvements</a>
+</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 caller's
-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>
-
-<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>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>One of the main focuses of this release was performance tuning and bug
+ fixing. In addition to these, several new major changes occurred:</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>
-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>
+<ul>
+
+<li>Dale finished up the Tail Merging optimization in the code generator, and
+ enabled it by default. This produces smaller code that is also faster in
+ some cases.</li>
+
+<li>Christopher Lamb implemented support for virtual register sub-registers,
+ which can be used to better model many forms of subregisters. As an example
+ use, he modified the X86 backend to use this to model truncates and
+ extends more accurately (leading to better code).</li>
+
+<li>Dan Gohman changed the way we represent vectors before legalization,
+ significantly simplifying the SelectionDAG representation for these and
+ making the code generator faster for vector code.</li>
+
+<li>Evan contributed a new target independent if-converter. While it is
+ target independent, so far only the ARM backend uses it.</li>
+
+<li>Evan rewrote the way the register allocator handles rematerialization,
+ allowing it to be much more effective on two-address targets like X86,
+ and taught it to fold loads away when possible (also a big win on X86).</li>
+
+<li>Dan Gohman contributed support for better alignment and volatility handling
+ in the code generator, and significantly enhanced alignment analysis for SSE
+ load/store instructions. With his changes, an insufficiently-aligned SSE
+ load instruction turns into <tt>movups</tt>, for example.</li>
+
+<li>Duraid Madina contributed a new "bigblock" register allocator, and Roman
+ Levenstein contributed several big improvements. BigBlock is optimized for
+ code that uses very large basic blocks. It is slightly slower than the
+ "local" allocator, but produces much better code.</li>
+
+<li>David Greene refactored the register allocator to split coalescing out from
+ allocation, making coalescers pluggable.</li>
+
+</ul>
</div>
-<!--_________________________________________________________________________-->
-<div class="doc_subsubsection">Other New Features</div>
+
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="targetspecific">Target Specific Improvements</a>
+</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 mostly 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>
- <li>The PowerPC backend generates far better code than in LLVM 1.4.</li>
-</ol>
+<p>New features include:
+</p>
+
+<ul>
+<li>Bruno Cardoso Lopes contributed initial MIPS support. It is sufficient to
+ run many small programs, but is still incomplete and is not yet
+ fully performant.</li>
+
+<li>Bill Wendling added SSSE3 support to the X86 backend.</li>
+
+<li>Nicholas Geoffray contributed improved linux/ppc ABI and JIT support.</li>
+
+<li>Dale Johannesen rewrote handling of 32-bit float values in the X86 backend
+ when using the floating point stack, fixing several nasty bugs.</li>
+
+<li>Dan contributed rematerialization support for the X86 backend, in addition
+ to several X86-specific micro optimizations.</li>
+</ul>
+
</div>
+
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="codequality">Code Quality Improvements in LLVM 1.5</a>
+<a name="llvmgccimprovements">llvm-gcc Improvements</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>
+<p>New features include:
+</p>
-<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>
+<ul>
+<li>Duncan and Anton made significant progress chasing down a number of problems
+ with C++ Zero-Cost exception handling in llvm-gcc 4.0 and 4.2. It is now at
+ the point where it "just works" on linux/X86-32 and has partial support on
+ other targets.</li>
-<li>Loops with trip counts based on array pointer comparisons (e.g. "<tt>for (i
-= 0; &A[i] != &A[100]; ++i) ...</tt>") are optimized better than before,
-which primarily helps iterator-intensive C++ codes.</li>
+<li>Devang and Duncan fixed a huge number of bugs relating to bitfields, pragma
+ pack, and variable sized fields in structures.</li>
-<li>The code generator now can provide and use information about commutative
-two-address instructions when performing register allocation.</li>
+<li>Tanya implemented support for <tt>__attribute__((noinline))</tt> in
+ llvm-gcc, and added support for generic variable annotations which are
+ propagated into the LLVM IR, e.g.
+ "<tt>int X __attribute__((annotate("myproperty")));</tt>".</li>
-<li>The optimizer now eliminates simple cases where redundant conditions exist
-between neighboring blocks.</li>
+<li>Sheng Zhou and Christopher Lamb implemented alias analysis support for
+"restrict" pointer arguments to functions.</li>
-<li>The reassociation pass (which turns (1+X+3) into (X+1+3) among other
-things), is more aggressive an intelligent.</li>
-
-</ol>
+<li>Duncan contributed support for trampolines (taking the address of a nested
+ function). Currently this is only supported on the X86-32 target.</li>
+
+<li>Lauro Ramos Venancio contributed support to encode alignment info in
+ load and store instructions, the foundation for other alignment-related
+ work.</li>
+</ul>
+
</div>
+
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="bugfix">Significant Bugs Fixed in LLVM 1.5</a>
+<a name="coreimprovements">LLVM Core Improvements</a>
</div>
<div class="doc_text">
+<p>New features include:
+</p>
+<ul>
+<li>Neil Booth contributed a new "APFloat" class, which ensures that floating
+ point representation and constant folding is not dependent on the host
+ architecture that builds the application. This support is the foundation
+ for "long double" support that will be wrapped up in LLVM 2.2.</li>
+
+<li>Based on the APFloat class, Dale redesigned the internals of the ConstantFP
+ class and has been working on extending the core and optimizer components to
+ support various target-specific 'long double's. We expect this work to be
+ completed in LLVM 2.2.</li>
-<p>Bugs fixed in the LLVM Core:</p>
-<ol>
- <li><a href="http://llvm.cs.uiuc.edu/PR491">[dse] DSE deletes stores that
- are partially overwritten by smaller stores</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR548">[instcombine] miscompilation of
- setcc or setcc in one case</a></li>
- <li>Transition code for LLVM 1.0 style varargs was removed from the .ll file
- parser. LLVM 1.0 bytecode files are still supported. </li>
-</ol>
+<li>LLVM now provides an LLVMBuilder class, which makes it significantly easier
+ to create LLVM IR instructions.</li>
-<p>Code Generator Bugs:</p>
-<ol>
- <li><a href="http://llvm.cs.uiuc.edu/PR490">[cbackend] Logical constant
- expressions (and/or/xor) not implemented</a>.</li>
- <li><a href="http://llvm.cs.uiuc.edu/PR511">[cbackend] C backend does not
- respect 'volatile'</a>.</li>
- <li>The JIT sometimes miscompiled globals and constant pool entries for
- 64-bit integer constants on 32-bit hosts.</li>
-</ol>
+<li>Reid contributed support for intrinsics that take arbitrary integer typed
+ arguments. Dan Gohman and Chandler extended it to support arbitrary
+ floating point arguments and vectors.</li>
+</ul>
+
+</div>
-<p>Bugs in the C/C++ front-end:</p>
-<ol>
- <li><a href="http://llvm.cs.uiuc.edu/PR487">[llvmgcc] llvm-gcc incorrectly
- rejects some constant initializers involving the addresses of array
- elements</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR501">[llvm-g++] Crash compiling
- anonymous union</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR509">[llvm-g++] Do not use dynamic
- initialization where static init will do</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR510">[llvmgcc] Field offset
- miscalculated for some structure fields following bit fields</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR513">[llvm-g++] Temporary lifetimes
- incorrect for short circuit logical operations</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR517">[llvm-gcc] Crash compiling
- bitfield <-> aggregate assignment</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR520">[llvm-g++] Error compiling
- virtual function thunk with an unnamed argument</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR522">[llvm-gcc] Crash on certain
- C99 complex number routines</a></li>
- <li><a href="http://llvm.cs.uiuc.edu/PR529">[llvm-g++] Crash using placement
- new on an array type</a></li>
-</ol>
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="otherimprovements">Other Improvements</a>
+</div>
+<div class="doc_text">
+<p>New features include:
+</p>
+
+<ul>
+<li>Sterling Stein contributed a new BrainF frontend, located in llvm/examples.
+ This shows a some of the more modern APIs for building a front-end, and
+ demonstrates JIT compiler support.</li>
+
+<li>David Green contributed a new <tt>--enable-expensive-checks</tt> configure
+ option which enables STL checking, and fixed several bugs exposed by
+ it.</li>
+</ul>
+
</div>
<!-- *********************************************************************** -->
<p>LLVM is known to work on the following platforms:</p>
<ul>
-<li>Intel and AMD machines running Red Hat Linux and FreeBSD (and probably
- other unix-like systems).</li>
-<li>Sun UltraSPARC workstations running Solaris 8.</li>
+<li>Intel and AMD machines 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 10.2 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>PowerPC-based Mac OS X systems, running 10.2 and above.</li>
+<li>Sun UltraSPARC workstations running Solaris 8.</li>
<li>Alpha-based machines running Debian GNU/Linux.</li>
<li>Itanium-based machines running Linux and HP-UX.</li>
</ul>
<p>This section contains all known problems with the LLVM system, listed by
component. As new problems are discovered, they will be added to these
sections. If you run into a problem, please check the <a
-href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug database</a> and submit a bug if
+href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
there isn't already one.</p>
</div>
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 llvmdev list.</p>
+components, please contact us on the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
<ul>
-<li>The following passes are incomplete or buggy, and may be removed in future
- releases: <tt>-cee, -branch-combine, -instloops, -paths, -pre</tt></li>
-<li>The <tt>llvm-db</tt> tool is in a very early stage of development, but can
- be used to step through programs and inspect the stack.</li>
-<li>The "iterative scan" register allocator (enabled with
- <tt>-regalloc=iterativescan</tt>) is not stable.</li>
-<li>The SparcV8, Alpha, and IA64 code generators are experimental.</li>
+<li>The <tt>-cee</tt> pass is known to be buggy, and may be removed in a
+ future release.</li>
+<li>The MSIL backend is experimental.</li>
+<li>The IA64 code generator is experimental.</li>
+<li>The Alpha backend is experimental.</li>
+<li>"<tt>-filetype=asm</tt>" (the default) is the only supported value for the
+ <tt>-filetype</tt> llc option.</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
- <a name="core">Known problems with the LLVM Core</a>
+ <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 <a href="http://llvm.org/PR879">inline
+ assembly that uses the X86 floating point stack</a>.</li>
+<li>The X86 backend occasionally has <a href="http://llvm.org/PR1649">alignment
+ problems</a> on operating systems that don't require 16-byte stack alignment
+ (including most non-darwin OS's like linux).</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><a href="http://llvm.org/PR642">PowerPC backend does not correctly
+implement ordered FP comparisons</a>.</li>
+<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="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>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
+made where the argument is not 16-byte aligned, as required on IA64. (Strictly
+speaking this is not a bug in the IA64 back-end; it will also be encountered
+when building C++ programs using the C back-end.)</li>
+
+<li>The C++ front-end does not use <a href="http://llvm.org/PR406">IA64
+ABI compliant layout of v-tables</a>. In particular, it just stores function
+pointers instead of function descriptors in the vtable. This bug prevents
+mixing C++ code compiled with LLVM with C++ objects compiled by other C++
+compilers.</li>
+
+<li>There are a few ABI violations which will lead to problems when mixing LLVM
+output with code built with other compilers, particularly for floating-point
+programs.</li>
+
+<li>Defining vararg functions is not supported (but calling them is ok).</li>
+
+<li>The Itanium backend has bitrotted somewhat.</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>In the JIT, <tt>dlsym()</tt> on a symbol compiled by the JIT will not
- work.</li>
- <li>The JIT does not use mutexes to protect its internal data structures. As
- such, execution of a threaded program could cause these data structures to be
- corrupted.
- </li>
- <li><a href="http://llvm.cs.uiuc.edu/PR240">The lower-invoke pass does not
- mark values live across a setjmp as volatile</a>. This missing feature
- only affects targets whose setjmp/longjmp libraries do not save and restore
- the entire register file.</li>
+<li><a href="http://llvm.org/PR802">The C backend does not support inline
+ assembly code</a>.</li>
+<li><a href="http://llvm.org/PR1126">The C backend does not support vectors
+ yet</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 LLC or native compilers.</li>
</ul>
+
</div>
+
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="c-fe">Known problems with the C front-end</a>
<div class="doc_subsubsection">Bugs</div>
<div class="doc_text">
-<ul>
-<li>C99 Variable sized arrays do not release stack memory when they go out of
- scope. Thus, the following program may run out of stack space:
-<pre>
- for (i = 0; i != 1000000; ++i) {
- int X[n];
- foo(X);
- }
-</pre></li>
-
-<li>Initialization of global union variables can only be done <a
-href="http://llvm.cs.uiuc.edu/PR162">with the largest union member</a>.</li>
-</ul>
+<p>llvm-gcc4 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>
+
</div>
<!-- _______________________________________________________________________ -->
</div>
<div class="doc_text">
-
<ul>
-<li>Inline assembly is not yet supported.</li>
-
-<li>"long double" is transformed by the front-end into "double". There is no
-support for floating point data types of any size other than 32 and 64
-bits.</li>
+<li><p>"long double" is silently transformed by the front-end into "double". There
+is no support for floating point data types of any size other than 32 and 64
+bits.</p></li>
-<li>The following Unix system functionality has not been tested and may not
-work:
- <ol>
- <li><tt>sigsetjmp</tt>, <tt>siglongjmp</tt> - These are not turned into the
- appropriate <tt>invoke</tt>/<tt>unwind</tt> instructions. Note that
- <tt>setjmp</tt> and <tt>longjmp</tt> <em>are</em> compiled correctly.
- <li><tt>getcontext</tt>, <tt>setcontext</tt>, <tt>makecontext</tt>
- - These functions have not been tested.
- </ol></li>
+<li><p>llvm-gcc does <b>not</b> support <tt>__builtin_apply</tt> yet.
+ See <a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</p>
+</li>
-<li>Although many GCC extensions are supported, some are not. In particular,
- the following extensions are known to <b>not be</b> supported:
+<li><p>llvm-gcc <b>partially</b> supports these GCC extensions:</p>
<ol>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>: As in Algol and Pascal, lexical scoping of functions.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended%20Asm">Extended Asm</a>: Assembler instructions with C expressions as operands.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html#Asm%20Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Explicit-Reg-Vars.html#Explicit%20Reg%20Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html#Vector%20Extensions">Vector Extensions</a>: Using vector instructions through built-in functions.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html#Target%20Builtins">Target Builtins</a>: Built-in functions specific to particular targets.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
- </ol>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>:
- <p>The following GCC extensions are <b>partially</b> supported. An ignored
- attribute means that the LLVM compiler ignores the presence of the attribute,
- but the code should still work. An unsupported attribute is one which is
- ignored by the LLVM compiler and will cause a different interpretation of
- the program.</p>
-
- <ol>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
- Arrays whose length is computed at run time.<br>
- Supported, but allocated stack space is not freed until the function returns (noted above).</li>
+ As in Algol and Pascal, lexical scoping of functions.
+ Nested functions are supported, but llvm-gcc does not support
+ taking the address of a nested function (except on the X86-32 target)
+ or non-local gotos.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
Declaring that functions have no side effects or that they can never
return.<br>
- <b>Supported:</b> <tt>format</tt>, <tt>format_arg</tt>, <tt>non_null</tt>,
- <tt>noreturn</tt>, <tt>constructor</tt>, <tt>destructor</tt>,
- <tt>unused</tt>,
- <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
-
- <b>Ignored:</b> <tt>noinline</tt>,
- <tt>always_inline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
- <tt>malloc</tt>, <tt>no_instrument_function</tt>, <tt>cdecl</tt><br>
-
- <b>Unsupported:</b> <tt>used</tt>, <tt>section</tt>, <tt>alias</tt>,
- <tt>visibility</tt>, <tt>regparm</tt>, <tt>stdcall</tt>,
- <tt>fastcall</tt>, all other target specific attributes</li>
-
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
- Specifying attributes of variables.<br>
- <b>Supported:</b> <tt>cleanup</tt>, <tt>common</tt>, <tt>nocommon</tt>,
- <tt>deprecated</tt>, <tt>transparent_union</tt>,
- <tt>unused</tt>, <tt>weak</tt><br>
-
- <b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>,
- <tt>section</tt>, <tt>shared</tt>, <tt>tls_model</tt>,
- <tt>vector_size</tt>, <tt>dllimport</tt>,
- <tt>dllexport</tt>, all target specific attributes.</li>
-
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.<br>
- <b>Supported:</b> <tt>transparent_union</tt>, <tt>unused</tt>,
- <tt>deprecated</tt>, <tt>may_alias</tt><br>
-
- <b>Unsupported:</b> <tt>aligned</tt>, <tt>packed</tt>,
- all target specific attributes.</li>
+ <b>Supported:</b> <tt>alias</tt>, <tt>always_inline</tt>, <tt>cdecl</tt>,
+ <tt>const</tt>, <tt>constructor</tt>, <tt>destructor</tt>,
+ <tt>deprecated</tt>, <tt>fastcall</tt>, <tt>format</tt>,
+ <tt>format_arg</tt>, <tt>non_null</tt>, <tt>noinline</tt>,
+ <tt>noreturn</tt>, <tt>pure</tt>, <tt>regparm</tt>
+ <tt>section</tt>, <tt>stdcall</tt>, <tt>unused</tt>, <tt>used</tt>,
+ <tt>visibility</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
- <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
- Other built-in functions.<br>
- We support all builtins which have a C language equivalent (e.g.,
- <tt>__builtin_cos</tt>), <tt>__builtin_alloca</tt>,
- <tt>__builtin_types_compatible_p</tt>, <tt>__builtin_choose_expr</tt>,
- <tt>__builtin_constant_p</tt>, and <tt>__builtin_expect</tt>
- (currently ignored). We also support builtins for ISO C99 floating
- point comparison macros (e.g., <tt>__builtin_islessequal</tt>),
- <tt>__builtin_prefetch</tt>, <tt>__builtin_popcount[ll]</tt>,
- <tt>__builtin_clz[ll]</tt>, and <tt>__builtin_ctz[ll]</tt>.</li>
+ <b>Ignored:</b> <tt>nothrow</tt>, <tt>malloc</tt>,
+ <tt>no_instrument_function</tt></li>
</ol>
+</li>
- <p>The following extensions <b>are</b> known to be supported:</p>
+<li><p>llvm-gcc supports the vast majority of GCC extensions, including:</p>
<ol>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
+ Other built-in functions.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
+ Specifying attributes of variables.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
+ Arrays whose length is computed at run time.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels%20as%20Values">Labels as Values</a>: Getting pointers to labels and computed gotos.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Typeof.html#Typeof">Typeof</a>: <code>typeof</code>: referring to the type of an expression.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html#Variadic%20Macros">Variadic Macros</a>: Macros with a variable number of arguments.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended%20Asm">Extended Asm</a>: Assembler instructions with C expressions as operands.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html#Asm%20Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Explicit-Reg-Vars.html#Explicit%20Reg%20Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html#Vector%20Extensions">Vector Extensions</a>: Using vector instructions through built-in functions.</li>
+ <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html#Target%20Builtins">Target Builtins</a>: Built-in functions specific to particular targets.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Subscripting.html#Subscripting">Subscripting</a>: Any array can be subscripted, even if not an lvalue.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html#Pointer%20Arith">Pointer Arith</a>: Arithmetic on <code>void</code>-pointers and function pointers.</li>
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
<div class="doc_text">
-<p>For this release, the C++ front-end is considered to be fully
+<p>The C++ front-end is considered to be fully
tested and works for a number of non-trivial programs, including LLVM
-itself.</p>
-
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Bugs</div>
-
-<div class="doc_text">
-
-<ul>
-<li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C
- front-end</a>.</li>
-
-<li><b>IA-64 specific</b>: The C++ front-end does not use <a
-href="http://llvm.cs.uiuc.edu/PR406">IA64 ABI compliant layout of v-tables</a>.
-In particular, it just stores function pointers instead of function
-descriptors in the vtable. This bug prevents mixing C++ code compiled with
-LLVM with C++ objects compiled by other C++ compilers.</li>
-
-</ul>
-
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">
- Notes
-</div>
-
-<div class="doc_text">
+itself, Qt, Mozilla, etc.</p>
<ul>
+<li>Exception handling only works well on the linux/X86-32 target.
+In some cases, illegally throwing an exception does not result
+in a call to terminate.</li>
-<li>The C++ front-end is based on a pre-release of the GCC 3.4 C++ parser. This
-parser is significantly more standards compliant (and picky) than prior GCC
-versions. For more information, see the C++ section of the <a
-href="http://gcc.gnu.org/gcc-3.4/changes.html">GCC 3.4 release notes</a>.</li>
+<!-- NO EH Support!
<li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
representation issues. Because we use this API, code generated by the LLVM
compilers should be binary compatible with machine code generated by other
Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
- <i>However</i>, the exception handling mechanism used by LLVM is very
+ <i>However</i>, the exception handling mechanism used by llvm-gcc3 is very
different from the model used in the Itanium ABI, so <b>exceptions will not
interact correctly</b>. </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>None yet</li>
+-->
</ul>
</div>
-<!-- ======================================================================= -->
-<div class="doc_subsection">
- <a name="sparcv9-be">Known problems with the SparcV9 back-end</a>
-</div>
-<div class="doc_text">
-
-<ul>
-<li><a href="http://llvm.cs.uiuc.edu/PR60">[sparcv9] SparcV9 backend miscompiles
-several programs in the LLVM test suite</a></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>None yet</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>The C back-end produces code that violates the ANSI C Type-Based Alias
-Analysis rules. As such, special options may be necessary to compile the code
-(for example, GCC requires the <tt>-fno-strict-aliasing</tt> option). This
-problem probably cannot be fixed.</li>
-
-<li><a href="http://llvm.cs.uiuc.edu/PR56">Zero arg vararg functions are not
-supported</a>. This should not affect LLVM produced by the C or C++
-frontends.</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 arithmatic sequences which may trap do not have the appropriate nops inserted to ensure restartability.</li>
-
-<li>Vararg functions are not supported.</li>
-
-<li>Due to the vararg problems, C++ exceptions do not work. Small changes are required to the CFE (which break correctness in the exception handler) to compile the exception handling library (and thus the C++ standard library).</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>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
-made where the argument is not 16-byte aligned, as required on IA64. (Strictly
-speaking this is not a bug in the IA64 back-end; it will also be encountered
-when building C++ programs using the C back-end.)</li>
-
-<li>There are a few ABI violations which will lead to problems
-when mixing LLVM output with code built with other compilers,
-particularly for C++ and floating-point programs.</li>
-
-<li>Vararg functions are not supported.</li>
-
-</ul>
-
-</div>
-
-<!-- ======================================================================= -->
-<div class="doc_subsection">
- <a name="sparcv8">Known problems with the SPARC-V8 back-end</a>
-</div>
-
-<div class="doc_text">
-
-<ul>
-<li>Many features are still missing (e.g. support for 64-bit integer
-arithmetic).</li>
-
-<li>This backend needs to be updated to use the SelectionDAG instruction
-selection framework.</li>
-</ul>
-
-</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<div class="doc_text">
-<p>A wide variety of additional information is available on the LLVM web page,
-including <a href="http://llvm.cs.uiuc.edu/docs/#maillist">mailing lists</a> and
-<a href="http://llvm.cs.uiuc.edu/pubs/">publications describing algorithms and
-components implemented in LLVM</a>. The web page also contains versions of the
-API documentation which is up-to-date with the CVS version of the source code.
+<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://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">mailing
+us via the <a href="http://llvm.org/docs/#maillist"> mailing
lists</a>.</p>
</div>
<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="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+ <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
</address>
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