<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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- <title>LLVM 1.8 Release Notes</title>
+ <title>LLVM 2.0 Release Notes</title>
</head>
<body>
-<div class="doc_title">LLVM 1.8 Release Notes</div>
+<div class="doc_title">LLVM 2.0 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
<div class="doc_text">
<p>This document contains the release notes for the LLVM compiler
-infrastructure, release 1.8. 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 (corresponding to LLVM CVS) can be found
-on the <a
-href="http://llvm.org/releases/">LLVM releases 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 2.0. Here we describe the status of LLVM, including any
+known problems and major improvements from the previous release. All LLVM
+releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
+releases web site</a>.
<p>For more information about LLVM, including information about the latest
release, please check out the <a href="http://llvm.org/">main LLVM
<div class="doc_text">
-<p>This is the nineth public release of the LLVM Compiler Infrastructure. This
-release incorporates a large number of enhancements and new features,
-including DWARF debugging support (C and C++ on Darwin/PPC), improved inline
-assembly support, a new <a href="http://llvm.org/nightlytest/">nightly
-tester</a>, llvm-config enhancements, many bugs
-fixed, and performance and compile time improvements.
-</p>
+<p>This is the eleventh public release of the LLVM Compiler Infrastructure.
+Being the first major release since 1.0, this release is different in several
+ways from our previous releases:</p>
+
+<ol>
+<li>We took this as an opportunity to
+break backwards compatibility with the LLVM 1.x bytecode and .ll file format.
+If you have LLVM 1.9 .ll files that you would like to upgrade to LLVM 2.x, we
+recommend the use of the stand alone <a href="#llvm-upgrade">llvm-upgrade</a>
+tool (which is included with 2.0). We intend to keep compatibility with .ll
+and .bc formats within the 2.x release series, like we did within the 1.x
+series.</li>
+<li>There are several significant change to the LLVM IR and internal APIs, such
+ as a major overhaul of the type system, the completely new bitcode file
+ format, etc (described below).</li>
+<li>We designed the release around a 6 month release cycle instead of the usual
+ 3-month cycle. This gave us extra time to develop and test some of the
+ more invasive features in this release.</li>
+<li>LLVM 2.0 no longer supports the llvm-gcc3 front-end. Users are required to
+ upgrade to llvm-gcc4. llvm-gcc4 includes many features over
+ llvm-gcc3, is faster, and is <a href="CFEBuildInstrs.html">much easier to
+ build from source</a>.</li>
+</ol>
+
+<p>Note that while this is a major version bump, this release has been
+ extensively tested on a wide range of software. It is easy to say that this
+ is our best release yet, in terms of both features and correctness. This is
+ the first LLVM release to correctly compile and optimize major software like
+ LLVM itself, Mozilla/Seamonkey, Qt 4.3rc1, kOffice, etc out of the box on
+ linux/x86.
+ </p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="newfeatures">New Features in LLVM 1.8</a>
+<a name="newfeatures">New Features in LLVM 2.0</a>
</div>
<!--_________________________________________________________________________-->
-<div class="doc_subsubsection"><a name="dwarf">DWARF debugging
-support </a></div>
-
+<div class="doc_subsubsection"><a name="majorchanges">Major Changes</a></div>
<div class="doc_text">
-<p>The llvm-gcc4 C front-end now generates debugging info for C and C++. This
-information is propagated through the compiler and the code generator can
-currently produce DWARF debugging information from it. DWARF is a standard
-debugging format used on many platforms, but currently LLVM only includes
-target support for Mac OS X targets for the 1.8 release.
-</p>
+<p>Changes to the LLVM IR itself:</p>
+
+<ul>
+
+<li>Integer types are now completely signless. This means that we
+ have types like i8/i16/i32 instead of ubyte/sbyte/short/ushort/int
+ etc. LLVM operations that depend on sign have been split up into
+ separate instructions (<a href="http://llvm.org/PR950">PR950</a>). This
+ eliminates cast instructions that just change the sign of the operands (e.g.
+ int -> uint), which reduces the size of the IR and makes optimizers
+ simpler to write.</li>
+
+<li>Integer types with arbitrary bitwidths (e.g. i13, i36, i42, i1057, etc) are
+ now supported in the LLVM IR and optimizations (<a
+ href="http://llvm.org/PR1043">PR1043</a>). However, neither llvm-gcc
+ (<a href="http://llvm.org/PR1284">PR1284</a>) nor the native code generators
+ (<a href="http://llvm.org/PR1270">PR1270</a>) support non-standard width
+ integers yet.</li>
+
+<li>'Type planes' have been removed (<a href="http://llvm.org/PR411">PR411</a>).
+ It is no longer possible to have two values with the same name in the
+ same symbol table. This simplifies LLVM internals, allowing significant
+ speedups.</li>
+
+<li>Global variables and functions in .ll files are now prefixed with
+ @ instead of % (<a href="http://llvm.org/PR645">PR645</a>).</li>
+
+<li>The LLVM 1.x "bytecode" format has been replaced with a
+ completely new binary representation, named 'bitcode'. The <a
+ href="BitCodeFormat.html">Bitcode Format</a> brings a
+ number of advantages to the LLVM over the old bytecode format: it is denser
+ (files are smaller), more extensible, requires less memory to read,
+ is easier to keep backwards compatible (so LLVM 2.5 will read 2.0 .bc
+ files), and has many other nice features.</li>
+
+<li>Load and store instructions now track the alignment of their pointer
+ (<a href="http://www.llvm.org/PR400">PR400</a>). This allows the IR to
+ express loads that are not sufficiently aligned (e.g. due to '<tt>#pragma
+ packed</tt>') or to capture extra alignment information.</li>
+</ul>
+
+<p>Major new features:</p>
+
+<ul>
+
+<li>A number of ELF features are now supported by LLVM, including 'visibility',
+ extern weak linkage, Thread Local Storage (TLS) with the <tt>__thread</tt>
+ keyword, and symbol aliases.
+ Among other things, this means that many of the special options needed to
+ configure llvm-gcc on linux are no longer needed, and special hacks to build
+ large C++ libraries like Qt are not needed.</li>
+
+<li>LLVM now has a new MSIL backend. llc -march=msil will now turn LLVM
+ into MSIL (".net") bytecode. This is still fairly early development
+ with a number of limitations.</li>
+
+</ul>
</div>
-<!--_________________________________________________________________________-->
-<div class="doc_subsubsection"><a name="inlineasm">Inline Assembly
-Support</a></div>
+<!--_________________________________________________________________________-->
+<div class="doc_subsubsection"><a name="llvmgccfeatures">llvm-gcc
+Improvements</a></div>
<div class="doc_text">
+<p>New features include:
+</p>
+
+<ul>
+<li>Precompiled Headers (PCH) are now supported.</li>
+
+<li>"<tt>#pragma packed</tt>" is now supported, as are the various features
+ described above (visibility, extern weak linkage, __thread, aliases,
+ etc).</li>
-<p>Inline assembly support is substantially improved in LLVM 1.8 over LLVM 1.7.
-Many unsupported features are now supported, and inline asm support in the X86
-backend is far better. llvm-gcc4 now supports global register variables as
-well.</p>
+<li>Tracking function parameter/result attributes is now possible.</li>
+<li>Many internal enhancements have been added, such as improvements to
+ NON_LVALUE_EXPR, arrays with non-zero base, structs with variable sized
+ fields, VIEW_CONVERT_EXPR, CEIL_DIV_EXPR, nested functions, and many other
+ things. This is primarily to supports non-C GCC front-ends, like Ada.</li>
+
+<li>It is simpler to configure llvm-gcc for linux.</li>
+
+</ul>
+
</div>
<!--_________________________________________________________________________-->
-<div class="doc_subsubsection"><a name="loopopt">Loop Optimizer Improvements</a></div>
+<div class="doc_subsubsection"><a name="optimizer">Optimizer
+Improvements</a></div>
<div class="doc_text">
-
-<p>The loop optimizer passes now uses "Loop-Closed SSA Form", which makes it
-easier to update SSA form as loop transformations change the code. An
-immediate benefit of this is that the loop unswitching pass can now unswitch
-loops in more cases.
+<p>New features include:
</p>
+<ul>
+<li>The <a href="WritingAnLLVMPass.html">pass manager</a> has been entirely
+ rewritten, making it significantly smaller, simpler, and more extensible.
+ Support has been added to run FunctionPasses interlaced with
+ CallGraphSCCPasses, and we now support loop transformations explicitly with
+ LoopPass.</li>
+
+<li>The <tt>-scalarrepl</tt> pass can now promote unions containing FP values
+ into a register, it can also handle unions of vectors of the same
+ size.</li>
+
+<li>LLVM 2.0 includes a new loop rotation pass, which converts "for loops" into
+ "do/while loops", where the condition is at the bottom of the loop.</li>
+
+<li>The Loop Strength Reduction pass has been improved, and support added
+ for sinking expressions across blocks to reduce register pressure.</li>
+
+<li>ModulePasses may now use the result of FunctionPasses.</li>
+
+<li>The [Post]DominatorSet classes have been removed from LLVM and clients
+ switched to use the far-more-efficient ETForest class instead.</li>
+
+<li>The ImmediateDominator class has also been removed, and clients have been
+ switched to use DominatorTree instead.</li>
+
+<li>The predicate simplifier pass has been improved, making it able to do
+ simple value range propagation and eliminate more conditionals.</li>
+
+</ul>
+
</div>
<!--_________________________________________________________________________-->
-<div class="doc_subsubsection"><a name="jumptab">Jump Table Support for Switches
-</a></div>
+<div class="doc_subsubsection"><a name="codegen">Code
+Generator Enhancements</a></div>
<div class="doc_text">
+<p>
+New features include:
+</p>
+
+<ul>
+
+<li>Support was added for software floating point, which allows LLVM to target
+ chips that don't have hardware FPUs (e.g. ARM thumb mode).</li>
+
+<li>A new register scavenger has been implemented, which is useful for
+ finding free registers after register allocation. This is useful when
+ rewriting frame references on RISC targets, for example.</li>
+
+<li>Heuristics have been added to avoid coalescing vregs with very large live
+ ranges to physregs. This was bad because it effectively pinned the physical
+ register for the entire lifetime of the virtual register (<a
+ href="http://llvm.org/PR711">PR711</a>).</li>
+
+<li>Support now exists for very simple (but still very useful)
+ rematerialization the register allocator, enough to move
+ instructions like "load immediate" and constant pool loads.</li>
+
+<li>Switch statement lowering is significantly better, improving codegen for
+ sparse switches that have dense subregions, and implemented support
+ for the shift/and trick.</li>
-<p>The code generator now lowers switch statements to jump tables, providing
-significant performance boosts for applications (e.g. interpreters) whose
-performance is highly correlated to switch statement performance.</p>
+<li>Added support for tracking physreg sub-registers and super-registers
+ in the code generator, as well as extensive register
+ allocator changes to track them.</li>
+
+<li>There is initial support for virtreg sub-registers
+ (<a href="http://llvm.org/PR1350">PR1350</a>).</li>
+
+</ul>
+
+<p>
+Other improvements include:
+</p>
+
+<ul>
+
+<li>Inline assembly support is much more solid that before.
+ The two primary features still missing are support for 80-bit floating point
+ stack registers on X86 (<a href="http://llvm.org/PR879">PR879</a>), and
+ support for inline asm in the C backend (<a
+ href="http://llvm.org/PR802">PR802</a>).</li>
+
+<li>DWARF debug information generation has been improved. LLVM now passes
+ most of the GDB testsuite on MacOS and debug info is more dense.</li>
+
+<li>Codegen support for Zero-cost DWARF exception handling has been added (<a
+ href="http://llvm.org/PR592">PR592</a>). It is mostly
+ complete and just in need of continued bug fixes and optimizations at
+ this point. However, support in llvm-g++ is disabled with an
+ #ifdef for the 2.0 release (<a
+ href="http://llvm.org/PR870">PR870</a>).</li>
+
+<li>The code generator now has more accurate and general hooks for
+ describing addressing modes ("isLegalAddressingMode") to
+ optimizations like loop strength reduction and code sinking.</li>
+
+<li>Progress has been made on a direct Mach-o .o file writer. Many small
+ apps work, but it is still not quite complete.</li>
+
+</ul>
+
+<p>In addition, the LLVM target description format has itself been extended in
+ several ways:</p>
+
+<ul>
+<li>Extended TargetData to support better target parameterization in
+ the .ll/.bc files, eliminating the 'pointersize/endianness' attributes
+ in the files (<a href="http://llvm.org/PR761">PR761</a>).</li>
+
+<li>TargetData was generalized for finer grained alignment handling,
+ handling of vector alignment, and handling of preferred alignment</li>
+
+<li>LLVM now supports describing target calling conventions
+ explicitly in .td files, reducing the amount of C++ code that needs
+ to be written for a port.</li>
+
+</ul>
</div>
<!--_________________________________________________________________________-->
-<div class="doc_subsubsection"><a name="jitrelease">Deallocation of JIT'd
-Machine Code
-</a></div>
+<div class="doc_subsubsection"><a name="specifictargets">Target-Specific
+Improvements</a></div>
<div class="doc_text">
-<p>The LLVM JIT now allows clients to deallocate machine code JIT'd to its code
-buffer. This is important for long living applications that depend on the JIT.
+<p>X86-specific Code Generator Enhancements:
</p>
+<ul>
+<li>The MMX instruction set is now supported through intrinsics.</li>
+<li>The scheduler was improved to better reduce register pressure on
+ X86 and other targets that are register pressure sensitive.</li>
+<li>Linux/x86-64 support is much better.</li>
+<li>PIC support for linux/x86 has been added.</li>
+<li>The X86 backend now supports the GCC regparm attribute.</li>
+<li>LLVM now supports inline asm with multiple constraint letters per operand
+ (like "ri") which is common in X86 inline asms.</li>
+</ul>
+
+<p>ARM-specific Code Generator Enhancements:</p>
+
+<ul>
+<li>The ARM code generator is now stable and fully supported.</li>
+
+<li>There are major new features, including support for ARM
+ v4-v6 chips, vfp support, soft float point support, pre/postinc support,
+ load/store multiple generation, constant pool entry motion (to support
+ large functions), and inline asm support, weak linkage support, static
+ ctor/dtor support and many bug fixes.</li>
+<li>Added support for Thumb code generation (<tt>llc -march=thumb</tt>).</li>
+
+<li>The ARM backend now supports the ARM AAPCS/EABI ABI and PIC codegen on
+ arm/linux.</li>
+
+<li>Several bugs were fixed for DWARF debug info generation on arm/linux.</li>
+</ul>
+
+<p>PowerPC-specific Code Generator Enhancements:</p>
+
+<ul>
+<li>The PowerPC 64 JIT now supports addressing code loaded above the 2G
+ boundary.</li>
+
+<li>Improved support for the Linux/ppc ABI and the linux/ppc JIT is fully
+ functional now. llvm-gcc and static compilation are not fully supported
+ yet though.</li>
+
+<li>Many PowerPC 64 bug fixes.</li>
+
+</ul>
+
</div>
+
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="other">Other Improvements</a></div>
-
<div class="doc_text">
-<p>This release includes many other improvements, including improvements to
- the optimizers and code generators (improving the generated code) changes to
- speed up the compiler in many ways (improving algorithms and fine tuning
- code), and changes to reduce the code size of the compiler itself.</p>
+<p>This release includes many other improvements, including
+performance work, specifically designed to tune datastructure
+usage. This makes several critical components faster.</p>
<p>More specific changes include:</p>
<ul>
-<li>LLVM 1.8 includes an initial ARM backend. This backend is in early
- development stages.</li>
-<li>LLVM 1.8 now includes significantly better support for mingw and
- cygwin.</li>
-<li>The <a href="CommandGuide/html/llvm-config.html">llvm-config</a> tool is
- now built by default and has several new features.</li>
-<li>The X86 and PPC backends now use the correct platform ABI for passing
- vectors as arguments to functions.</li>
-<li>The X86 backend now includes support for the Microsoft ML assembler
- ("MASM").</li>
-<li>The PowerPC backend now pattern matches the 'rlwimi' instruction more
- aggressively.</li>
-<li>Most of LLVM is now built with "-pedantic", ensuring better portability
- to more C++ Compilers.</li>
-<li>The PowerPC backend now includes initial 64-bit support. The JIT is not
- complete, and the static compiler has a couple of known bugs, but support
- is mostly in place. LLVM 1.9 will include completed PPC-64 support. </li>
+<li>LLVM no longer relies on static destructors to shut itself down. Instead,
+ it lazily initializes itself and shuts down when llvm_shutdown() is
+ explicitly called.</li>
-</ul>
-</div>
+<li>LLVM now has significantly fewer static constructors, reducing startup time.
+ </li>
-<!--=========================================================================-->
-<div class="doc_subsection">
-<a name="changes">Significant Changes in LLVM 1.8</a>
+<li>Several classes have been refactored to reduce the amount of code that
+ gets linked into apps that use the JIT.</li>
+
+<li>Construction of intrinsic function declarations has been simplified.</li>
+
+<li>The llvm-upgrade tool now exists. This migrates LLVM 1.9 .ll files to
+ LLVM 2.0 syntax.</li>
+
+<li>The gccas/gccld tools have been removed.</li>
+
+<li>Support has been added to llvm-test for running on low-memory
+ or slow machines (make SMALL_PROBLEM_SIZE=1).</li>
+
+<li>llvm-test is now more portable and should build with MS Visual Studio.</li>
+
+</ul>
</div>
+<!--_________________________________________________________________________-->
+<div class="doc_subsubsection"><a name="apichanges">API Changes</a></div>
<div class="doc_text">
+
+<p>LLVM 2.0 contains a revamp of the type system and several other significant
+internal changes. If you are programming to the C++ API, be aware of the
+following major changes:</p>
+
<ul>
-<li>The LLVM "SparcV9" backend (deprecated in LLVM 1.7) has been removed in
-LLVM 1.8. The LLVM "Sparc" backend replaces it.</li>
-<li>The --version option now prints more useful information, including the
- build configuration for the tool.</li>
+<li>Pass registration is slightly different in LLVM 2.0 (you now need an
+ intptr_t in your constructor), as explained in the <a
+ href="WritingAnLLVMPass.html#basiccode">Writing an LLVM Pass</a>
+ document.</li>
+
+<li><tt>ConstantBool</tt>, <tt>ConstantIntegral</tt> and <tt>ConstantInt</tt>
+ classes have been merged together, we now just have
+ <tt>ConstantInt</tt>.</li>
+
+<li><tt>Type::IntTy</tt>, <tt>Type::UIntTy</tt>, <tt>Type::SByteTy</tt>, ... are
+ replaced by <tt>Type::Int8Ty</tt>, <tt>Type::Int16Ty</tt>, etc. LLVM types
+ have always corresponded to fixed size types
+ (e.g. long was always 64-bits), but the type system no longer includes
+ information about the sign of the type.</li>
+
+<li>Several classes (<tt>CallInst</tt>, <tt>GetElementPtrInst</tt>,
+ <tt>ConstantArray</tt>, etc), that once took <tt>std::vector</tt> as
+ arguments now take ranges instead. For example, you can create a
+ <tt>GetElementPtrInst</tt> with code like:
+
+ <pre>
+ Value *Ops[] = { Op1, Op2, Op3 };
+ GEP = new GetElementPtrInst(BasePtr, Ops, 3);
+ </pre>
+
+ This avoids creation of a temporary vector (and a call to malloc/free). If
+ you have an std::vector, use code like this:
+ <pre>
+ std::vector<Value*> Ops = ...;
+ GEP = new GetElementPtrInst(BasePtr, &Ops[0], Ops.size());
+ </pre>
+
+ </li>
+
+<li>CastInst is now abstract and its functionality is split into several parts,
+ one for each of the <a href="LangRef.html#convertops">new cast
+ instructions</a>.</li>
+
+<li><tt>Instruction::getNext()/getPrev()</tt> are now private (along with
+ <tt>BasicBlock::getNext</tt>, etc), for efficiency reasons (they are now no
+ longer just simple pointers). Please use BasicBlock::iterator, etc instead.
+</li>
+
+<li><tt>Module::getNamedFunction()</tt> is now called
+ <tt>Module::getFunction()</tt>.</li>
+
+<li><tt>SymbolTable.h</tt> has been split into <tt>ValueSymbolTable.h</tt> and
+<tt>TypeSymbolTable.h</tt>.</li>
</ul>
</div>
<li>Sun UltraSPARC workstations running Solaris 8.</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 and X86-based Mac OS X systems, running 10.2 and above.</li>
+<li>PowerPC and X86-based Mac OS X systems, running 10.2 and above in 32-bit and
+ 64-bit modes.</li>
<li>Alpha-based machines running Debian GNU/Linux.</li>
<li>Itanium-based machines running Linux and HP-UX.</li>
</ul>
<ul>
<li>The <tt>-cee</tt> pass is known to be buggy, and may be removed in in a
future release.</li>
+<li>C++ EH support</li>
<li>The IA64 code generator is experimental.</li>
<li>The Alpha JIT is experimental.</li>
<li>"<tt>-filetype=asm</tt>" (the default) is the only supported value for the
<!-- ======================================================================= -->
<div class="doc_subsection">
- <a name="build">Known problems with the Build System</a>
+ <a name="x86-be">Known problems with the X86 back-end</a>
</div>
<div class="doc_text">
<ul>
-<li>none yet</li>
+<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>
</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 Dwarf debugging informations.
+</ul>
+
+</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
- <a name="core">Known problems with the LLVM Core</a>
+ <a name="arm-be">Known problems with the ARM 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 Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
+processors, any thumb program compiled with LLVM crashes or produces 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>QEMU-ARM (<= 0.9.0) wrongly executes programs compiled with LLVM. A non-affected QEMU version must be used or this
+<a href="http://cvs.savannah.nongnu.org/viewcvs/qemu/target-arm/translate.c?root=qemu&r1=1.46&r2=1.47&makepatch=1&diff_format=h">
+patch</a> must be applied on QEMU.</li>
</ul>
+
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
- <a name="c-fe">Known problems with the C front-end</a>
+ <a name="sparc-be">Known problems with the SPARC back-end</a>
</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Bugs</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">
-<p>
-llvm-gcc3 has many significant problems that are fixed by llvm-gcc4.
-Two major ones include:</p>
+<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>With llvm-gcc3,
- 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>With llvm-gcc3, Initialization of global union variables can only be done <a
-href="http://llvm.org/PR162">with the largest union member</a>.</li>
+<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>
-<p>llvm-gcc4 is far more stable and produces better code than llvm-gcc3, but
-does not currently support Link-Time-Optimization or C++ Exception Handling,
-which llvm-gcc3 does.</p>
+</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 does not support inline
+ assembly code</a>.</li>
+</ul>
+
+</div>
+
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="c-fe">Known problems with the C front-end</a>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">Bugs</div>
+
+<div class="doc_text">
+
+<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>"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>Although many GCC extensions are supported, some are not. In particular,
- the following extensions are known to <b>not be</b> supported:
- <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>
-
- <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>
+<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><p>llvm-gcc <b>partially</b> supports tthese GCC extensions:</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>
+ <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.<br>
+ Nested functions are supported, but llvm-gcc does not support non-local
+ gotos or taking the address of a nested function.</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>used</tt>,
- <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
+ <b>Supported:</b> <tt>alias</tt>, <tt>always_inline</tt>, <tt>cdecl</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>noreturn</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>
- <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>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>used</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>
-
- <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>noinline</tt>, <tt>pure</tt>, <tt>const</tt>, <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">
+itself, Qt, Mozilla, etc.</p>
<ul>
-<li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C
- front-end</a>.</li>
-
-</ul>
-
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">
- Notes
-</div>
-
-<div class="doc_text">
+<li>llvm-gcc4 only has partial support for <a href="http://llvm.org/PR870">C++
+Exception Handling</a>, and it is not enabled by default.</li>
-<ul>
+<!-- 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="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.org/PR56">Zero arg vararg functions are not
-supported</a>. This should not affect LLVM produced by the C or C++
-frontends.</li>
-
-<li>The C backend does not correctly implement the <a
-href="LangRef.html#i_stacksave"><tt>llvm.stacksave</tt></a> or
-<a href="LangRef.html#i_stackrestore"><tt>llvm.stackrestore</tt></a>
-intrinsics. This means that some code compiled by it can run out of stack
-space if they depend on these (e.g. C99 varargs).</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="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>
-</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>
-
-</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="arm-be">Known problems with the ARM back-end</a>
-</div>
-<div class="doc_text">
-
-<ul>
-<li>The ARM backend is currently in early development stages, it is not
-ready for production use.</li>
-</ul>
-
-</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<div class="doc_text">
<p>A wide variety of additional information is available on the <a
-href="http://llvm.org">LLVM web page</a>, including <a
-href="http://llvm.org/docs/">documentation</a> and <a
-href="http://llvm.org/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.
+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 CVS
+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>
<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.org/">The LLVM Compiler Infrastructure</a><br>
+ <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
</address>
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