-
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- <title>LLVM 2.3 Release Notes</title>
+ <title>LLVM 2.5 Release Notes</title>
</head>
<body>
-<div class="doc_title">LLVM 2.3 Release Notes</div>
-
+<div class="doc_title">LLVM 2.5 Release Notes</div>
+
<ol>
<li><a href="#intro">Introduction</a></li>
- <li><a href="#whatsnew">What's New?</a></li>
+ <li><a href="#subproj">Sub-project Status Update</a></li>
+ <li><a href="#externalproj">External Projects Using LLVM 2.5</a></li>
+ <li><a href="#whatsnew">What's New in LLVM 2.5?</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="#knownproblems">Known Problems</a></li>
<li><a href="#additionalinfo">Additional Information</a></li>
</ol>
<div class="doc_author">
- <p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
+ <p>Written by the <a href="http://llvm.org">LLVM Team</a></p>
</div>
-<!-- Done through Week-of-Mon-20080324.txt -->
-
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="intro">Introduction</a>
<div class="doc_text">
-<p>This document contains the release notes for the LLVM compiler
-infrastructure, release 2.3. 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>This document contains the release notes for the LLVM Compiler
+Infrastructure, release 2.5. Here we describe the status of LLVM, including
+major improvements from the previous release and significant known problems.
+All LLVM releases may be downloaded from the <a
+href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
<p>For more information about LLVM, including information about the latest
release, please check out the <a href="http://llvm.org/">main LLVM
web site</a>. If you have questions or comments, the <a
-href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
-list</a> is a good place to send them.</p>
+href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's Mailing
+List</a> is a good place to send them.</p>
-<p>Note that if you are reading this file from a Subversion checkout or the
+<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
+current one. To see the release notes for a specific release, please see the
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
+<!-- Unfinished features in 2.5:
+ Machine LICM
+ Machine Sinking
+ target-specific intrinsics
+ gold lto plugin
+ pre-alloc splitter, strong phi elim
+ <tt>llc -enable-value-prop</tt>, propagation of value info
+ (sign/zero ext info) from one MBB to another
+ debug info for optimized code
+ interpreter + libffi
+ postalloc scheduler: anti dependence breaking, hazard recognizer?
+
+initial support for debug line numbers when optimization enabled, not useful in
+ 2.5 but will be for 2.6.
+
+ -->
+
+ <!-- for announcement email:
+ -->
+
<!-- *********************************************************************** -->
<div class="doc_section">
- <a name="whatsnew">What's New?</a>
+ <a name="subproj">Sub-project Status Update</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
+<p>
+The LLVM 2.5 distribution currently consists of code from the core LLVM
+repository —which roughly includes the LLVM optimizers, code generators
+and supporting tools — and the llvm-gcc repository. In addition to this
+code, the LLVM Project includes other sub-projects that are in development. The
+two which are the most actively developed are the <a href="#clang">Clang
+Project</a> and the <a href="#vmkit">VMKit Project</a>.
+</p>
+
+</div>
-<p>This is the fourteenth public release of the LLVM Compiler Infrastructure.
-It includes a large number of features and refinements from LLVM 2.2.</p>
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
</div>
-<!-- Unfinished features in 2.3:
- Machine LICM
- Machine Sinking
- LegalizeDAGTypes
- -->
+<div class="doc_text">
+
+<p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build
+a set of new 'LLVM native' front-end technologies for the LLVM optimizer and
+code generator. While Clang is not included in the LLVM 2.5 release, it is
+continuing to make major strides forward in all areas. Its C and Objective-C
+parsing and code generation support is now very solid. For example, it is
+capable of successfully building many real-world applications for X86-32
+and X86-64,
+including the <a href="http://wiki.freebsd.org/BuildingFreeBSDWithClang">FreeBSD
+kernel</a> and <a href="http://gcc.gnu.org/gcc-4.2/">gcc 4.2</a>. C++ is also
+making <a href="http://clang.llvm.org/cxx_status.html">incredible progress</a>,
+and work on templates has recently started. If you are
+interested in fast compiles and good diagnostics, we encourage you to try it out
+by <a href="http://clang.llvm.org/get_started.html">building from mainline</a>
+and reporting any issues you hit to the <a
+href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">Clang front-end mailing
+list</a>.</p>
+
+<p>In the LLVM 2.5 time-frame, the Clang team has made many improvements:</p>
+
+<ul>
+<li>Clang now has a new driver, which is focused on providing a GCC-compatible
+ interface.</li>
+<li>The X86-64 ABI is now supported, including support for the Apple
+ 64-bit Objective-C runtime and zero cost exception handling.</li>
+<li>Precompiled header support is now implemented.</li>
+<li>Objective-C support is significantly improved beyond LLVM 2.4, supporting
+ many features, such as Objective-C Garbage Collection.</li>
+<li>Variable length arrays are now fully supported.</li>
+<li>C99 designated initializers are now fully supported.</li>
+<li>Clang now includes all major compiler headers, including a
+ redesigned <i>tgmath.h</i> and several more intrinsic headers.</li>
+<li>Many many bugs are fixed and many features have been added.</li>
+</ul>
+</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="changes">Major Changes in LLVM 2.3</a>
+<a name="clangsa">Clang Static Analyzer</a>
</div>
<div class="doc_text">
-<p>LLVM 2.3 no longer supports llvm-gcc 4.0, it has been replaced with
- llvm-gcc 4.2.</p>
+<p>Previously announced in the last LLVM release, the Clang project also
+includes an early stage static source code analysis tool for <a
+href="http://clang.llvm.org/StaticAnalysis.html">automatically finding bugs</a>
+in C and Objective-C programs. The tool performs a growing set of checks to find
+bugs that occur on a specific path within a program.</p>
+
+<p>In the LLVM 2.5 time-frame there have been many significant improvements to
+the analyzer's core path simulation engine and machinery for generating
+path-based bug reports to end-users. Particularly noteworthy improvements
+include experimental support for full field-sensitivity and reasoning about heap
+objects as well as an improved value-constraints subengine that does a much
+better job of reasoning about inequality relationships (e.g., <tt>x > 2</tt>)
+between variables and constants.
-<p>LLVM 2.3 no longer includes the <tt>llvm-upgrade</tt> tool. It was useful
- for upgrading LLVM 1.9 files to LLVM 2.x syntax, but you can always use a
- previous LLVM release to do this. One nice impact of this is that the LLVM
- regression test suite no longer depends on llvm-upgrade, which makes it run
- faster.</p>
+<p>The set of checks performed by the static analyzer continues to expand, and
+future plans for the tool include full source-level inter-procedural analysis
+and deeper checks such as buffer overrun detection. There are many opportunities
+to extend and enhance the static analyzer, and anyone interested in working on
+this project is encouraged to get involved!</p>
+
+</div>
+
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a>
+</div>
-<p>The <tt>llvm2cpp</tt> tool has been folded into llc, use
- <tt>llc -march=cpp</tt> instead of <tt>llvm2cpp</tt>.</p>
+<div class="doc_text">
+<p>
+The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of
+a JVM and a CLI Virtual Machines (Microsoft .NET is an
+implementation of the CLI) using the Just-In-Time compiler of LLVM.</p>
-<p>LLVM API Changes:</p>
+<p>Following LLVM 2.5, VMKit has its second release that you can find on its
+<a href="http://vmkit.llvm.org/releases/">webpage</a>. The release includes
+bug fixes, cleanup and new features. The major changes are:</p>
<ul>
-<li>Several core LLVM IR classes have migrated to use the
- '<tt>FOOCLASS::Create(...)</tt>' pattern instead of '<tt>new
- FOOCLASS(...)</tt>' (e.g. where FOOCLASS=<tt>BasicBlock</tt>). We hope to
- standardize on <tt>FOOCLASS::Create</tt> for all IR classes in the future,
- but not all of them have been moved over yet.</li>
-<li>LLVM 2.3 renames the LLVMBuilder and LLVMFoldingBuilder classes to
- IRBuilder.</li>
-<li>MRegisterInfo was renamed to TargetRegisterInfo.</li>
-<li>The MappedFile class is gone, please use MemoryBuffer instead.</li>
-<li>The '<tt>-enable-eh</tt>' flag to llc has been removed. Now code should
- encode whether it is safe to omit unwind information for a function by
- tagging the Function object with the '<tt>nounwind</tt>' attribute.</li>
+
+<li>Ahead of Time compiler: compiles .class files to llvm .bc. VMKit uses this
+functionality to native compile the standard classes (e.g. java.lang.String).
+Users can compile AoT .class files into dynamic libraries and run them with the
+help of VMKit.</li>
+
+<li>New exception model: the dwarf exception model is very slow for
+exception-intensive applications, so the JVM has had a new implementation of
+exceptions which check at each function call if an exception happened. There is
+a low performance penalty on applications without exceptions, but it is a big
+gain for exception-intensive applications. For example the jack benchmark in
+Spec JVM98 is 6x faster (performance gain of 83%).</li>
+
+<li>User-level management of thread stacks, so that thread local data access
+at runtime is fast and portable. </li>
+
+<li>Implementation of biased locking for faster object synchronizations at
+runtime.</li>
+
+<li>New support for OSX/X64, Linux/X64 (with the Boehm GC) and Linux/ppc32.</li>
</ul>
</div>
+<!-- *********************************************************************** -->
+<div class="doc_section">
+ <a name="externalproj">External Projects Using LLVM 2.5</a>
+</div>
+<!-- *********************************************************************** -->
+
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="otherprojects">Other LLVM Sub-Projects</a>
+<a name="pure">Pure</a>
</div>
<div class="doc_text">
-
<p>
-<p>The <a href="http://clang.llvm.org/">clang project</a> is an effort to build
-a set of new 'llvm native' front-end technologies for the LLVM optimizer
-and code generator. Currently, its C and Objective-C support is maturing
-nicely, and it has advanced source-to-source analysis and transformation
-capabilities. If you are interested in building source-level tools for C and
-Objective-C (and eventually C++), you should take a look. However, note that
-clang is not an official part of the LLVM 2.3 release. If you are interested in
-this project, please see its <a href="http://clang.llvm.org/">web site</a>.</p>
+<a href="http://pure-lang.googlecode.com/">Pure</a>
+is an algebraic/functional programming language based on term rewriting.
+Programs are collections of equations which are used to evaluate expressions in
+a symbolic fashion. Pure offers dynamic typing, eager and lazy evaluation,
+lexical closures, a hygienic macro system (also based on term rewriting),
+built-in list and matrix support (including list and matrix comprehensions) and
+an easy-to-use C interface. The interpreter uses LLVM as a backend to
+ JIT-compile Pure programs to fast native code.</p>
+
+<p>In addition to the usual algebraic data structures, Pure also has
+MATLAB-style matrices in order to support numeric computations and signal
+processing in an efficient way. Pure is mainly aimed at mathematical
+applications right now, but it has been designed as a general purpose language.
+The dynamic interpreter environment and the C interface make it possible to use
+it as a kind of functional scripting language for many application areas.
+</p>
+</div>
+
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="ldc">LLVM D Compiler</a>
+</div>
+<div class="doc_text">
+<p>
+<a href="http://www.dsource.org/projects/ldc">LDC</a> is an implementation of
+the D Programming Language using the LLVM optimizer and code generator.
+The LDC project works great with the LLVM 2.5 release. General improvements in
+this
+cycle have included new inline asm constraint handling, better debug info
+support, general bugfixes, and better x86-64 support. This has allowed
+some major improvements in LDC, getting us much closer to being as
+fully featured as the original DMD compiler from DigitalMars.
</p>
+</div>
+
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="RoadsendPHP">Roadsend PHP</a>
+</div>
+<div class="doc_text">
+<p><a href="http://code.roadsend.com/rphp">Roadsend PHP</a> (rphp) is an open
+source implementation of the PHP programming
+language that uses LLVM for its optimizer, JIT, and static compiler. This is a
+reimplementation of an earlier project that is now based on LLVM.</p>
+</div>
+
+
+<!-- *********************************************************************** -->
+<div class="doc_section">
+ <a name="whatsnew">What's New in LLVM 2.5?</a>
+</div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>This release includes a huge number of bug fixes, performance tweaks, and
+minor improvements. Some of the major improvements and new features are listed
+in this section.
+</p>
</div>
<!--=========================================================================-->
<div class="doc_text">
-<p>LLVM 2.3 includes several major new capabilities:</p>
+<p>LLVM 2.5 includes several major new capabilities:</p>
<ul>
-<li><p>The biggest change in LLVM 2.3 is Multiple Return Value (MRV) support.
- MRVs allow LLVM IR to directly represent functions that return multiple
- values without having to pass them "by reference" in the LLVM IR. This
- allows a front-end to generate more efficient code, as MRVs are generally
- returned in registers if a target supports them. See the <a
- href="LangRef.html#i_getresult">LLVM IR Reference</a> for more details.</p>
-
- <p>MRVs are fully supported in the LLVM IR, but are not yet fully supported in
- on all targets. However, it is generally safe to return up to 2 values from
- a function: most targets should be able to handle at least that. MRV
- support is a critical requirement for X86-64 ABI support, as X86-64 requires
- the ability to return multiple registers from functions, and we use MRVs to
- accomplish this in a direct way.</p></li>
-
-
-<li><p>LLVM 2.3 includes a complete reimplementation of the "<tt>llvmc</tt>"
- tool. It is designed to overcome several problems with the original
- <tt>llvmc</tt> and to provide a superset of the features of the
- '<tt>gcc</tt>' driver.</p>
-
-<p>The main features of <tt>llvmc2</tt> are:
- <ul>
- <li>Extended handling of command line options and smart rules for
- dispatching them to different tools.</li>
- <li>Flexible (and extensible) rules for defining different tools.</li>
- <li>The different intermediate steps performed by tools are represented
- as edges in the abstract graph.</li>
- <li>The 'language' for driver behavior definition is tablegen and thus
- it's relatively easy to add new features.</li>
- <li>The definition of driver is transformed into set of C++ classes, thus
- no runtime interpretation is needed.</li>
- </ul></p>
- </li>
-
-
-<li><p>LLVM 2.3 includes a completely rewritten interface for <a
- href="LinkTimeOptimization.html">Link Time Optimization</a>. This interface
- is written in C, which allows for easier integration with C code bases, and
- incorporates improvements we learned about from the first incarnation of the
- interface.</p></li>
-
-<li><p>The <a href="tutorial/LangImpl1.html">Kaleidoscope tutorial</a> now
- includes a "port" of the tutorial that <a
- href="tutorial/OCamlLangImpl1.html">uses the Ocaml bindings</a> to implement
- the Kaleidoscope language.</p></li>
+<li>LLVM 2.5 includes a brand new <a
+href="http://en.wikipedia.org/wiki/XCore">XCore</a> backend.</li>
+<li>llvm-gcc now generally supports the GFortran front-end, and the precompiled
+release binaries now support Fortran, even on Mac OS/X.</li>
+
+<li>CMake is now used by the <a href="GettingStartedVS.html">LLVM build process
+on Windows</a>. It automatically generates Visual Studio project files (and
+more) from a set of simple text files. This makes it much easier to
+maintain. In time, we'd like to standardize on CMake for everything.</li>
+
+<li>LLVM 2.5 now uses (and includes) Google Test for unit testing.</li>
+
+<li>The LLVM native code generator now supports arbitrary precision integers.
+Types like <tt>i33</tt> have long been valid in the LLVM IR, but were previously
+only supported by the interpreter. Note that the C backend still does not
+support these.</li>
+
+<li>LLVM 2.5 no longer uses 'bison,' so it is easier to build on Windows.</li>
</ul>
</div>
<div class="doc_text">
-<p>LLVM 2.3 fully supports the llvm-gcc 4.2 front-end.</p>
-
-<p>llvm-gcc 4.2 includes numerous fixes to better support the Objective-C
-front-end. Objective-C now works very well on Mac OS/X.</p>
+<p>LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC
+front-ends and driver with the LLVM optimizer and code generator. It currently
+includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>
-<p>llvm-gcc 4.2 includes many other fixes which improve conformance with the
-relevant parts of the GCC testsuite.</p>
+<ul>
+<li>In this release, the GCC inliner is completely disabled. Previously the GCC
+inliner was used to handle always-inline functions and other cases. This caused
+problems with code size growth, and it is completely disabled in this
+release.</li>
+
+<li>llvm-gcc (and LLVM in general) now support code generation for stack
+canaries, which is an effective form of <a
+href="http://en.wikipedia.org/wiki/Stack-smashing_protection">buffer overflow
+protection</a>. llvm-gcc supports this with the <tt>-fstack-protector</tt>
+command line option (just like GCC). In LLVM IR, you can request code
+generation for stack canaries with function attributes.
+</li>
+</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="coreimprovements">LLVM Core Improvements</a>
+<a name="coreimprovements">LLVM IR and Core Improvements</a>
</div>
<div class="doc_text">
-<p>New features include:
-</p>
+<p>LLVM IR has several new features that are used by our existing front-ends and
+can be useful if you are writing a front-end for LLVM:</p>
+<ul>
+<li>The <a href="LangRef.html#i_shufflevector">shufflevector</a> instruction
+has been generalized to allow different shuffle mask width than its input
+vectors. This allows you to use shufflevector to combine two
+"<4 x float>" vectors into a "<8 x float>" for example.</li>
+
+<li>LLVM IR now supports new intrinsics for computing and acting on <a
+href="LangRef.html#int_overflow">overflow of integer operations</a>. This allows
+efficient code generation for languages that must trap or throw an exception on
+overflow. While these intrinsics work on all targets, they only generate
+efficient code on X86 so far.</li>
+
+<li>LLVM IR now supports a new <a href="LangRef.html#linkage">private
+linkage</a> type to produce labels that are stripped by the assembler before it
+produces a .o file (thus they are invisible to the linker).</li>
+
+<li>LLVM IR supports two new attributes for better alias analysis. The <a
+href="LangRef.html#paramattrs">noalias</a> attribute can now be used on the
+return value of a function to indicate that it returns new memory (e.g.
+'malloc', 'calloc', etc).
+The new <a href="LangRef.html#paramattrs">nocapture</a> attribute can be used
+on pointer arguments to indicate that the function does not return the pointer,
+store it in an object that outlives the call, or let the value of the pointer
+escape from the function in any other way.
+Note that it is the pointer itself that must not escape, not the value it
+points to: loading a value out of the pointer is perfectly fine.
+Many standard library functions (e.g. 'strlen', 'memcpy') have this property.
+<!-- The simplifylibcalls pass applies these attributes to standard libc functions. -->
+</li>
-Common linkage?
+<li>The parser for ".ll" files in lib/AsmParser is now completely rewritten as a
+recursive descent parser. This parser produces better error messages (including
+caret diagnostics), is less fragile (less likely to crash on strange things),
+does not leak memory, is more efficient, and eliminates LLVM's last use of the
+'bison' tool.</li>
-Atomic operation support, Alpha, X86, X86-64, PowerPC. "__sync_synchronize",
-"__sync_val_compare_and_swap", etc
+<li>Debug information representation and manipulation internals have been
+ consolidated to use a new set of classes in
+ <tt>llvm/Analysis/DebugInfo.h</tt>. These routines are more
+ efficient, robust, and extensible and replace the older mechanisms.
+ llvm-gcc, clang, and the code generator now use them to create and process
+ debug information.</li>
-<ul>
-<li>The C and Ocaml bindings have received additional improvements. The
-bindings now cover pass managers, several transformation passes, iteration
-over the LLVM IR, target data, and parameter attribute lists.</li>
</ul>
-
+
</div>
<!--=========================================================================-->
<div class="doc_text">
-<p>In addition to a huge array of bug fixes and minor performance tweaks, the
-LLVM 2.3 optimizers support a few major enhancements:</p>
+<p>In addition to a large array of bug fixes and minor performance tweaks, this
+release includes a few major enhancements and additions to the optimizers:</p>
<ul>
-<li>Loop index set splitting on by default.<p>
-This transformation hoists conditions from loop bodies and reduces loop's
-iteration space to improve performance. For example, <p>
-<pre>
-for (i = LB; i < UB; ++i)
- if (i <= NV)
- LOOP_BODY
-</pre>
-is transformed into
-<pre>
-NUB = min(NV+1, UB)
-for (i = LB; i < NUB; ++i)
- LOOP_BODY
-</pre>
-</li>
+<li>The loop optimizer now improves floating point induction variables in
+several ways, including adding shadow induction variables to avoid
+"integer <-> floating point" conversions in loops when safe.</li>
-<li>LLVM includes a new <tt>memcpy</tt> optimization pass removes
-dead <tt>memcpy</tt> calls, unneeded copies of aggregates, and performs
-return slot optimization. The LLVM optimizer now notices long sequences of
-consecutive stores and merges them into <tt>memcpy</tt>'s where profitable.</li>
+<li>The "-mem2reg" pass is now much faster on code with large basic blocks.</li>
-<li>Alignment detection for vector memory references and for <tt>memcpy</tt> and
-<tt>memset</tt> is now more aggressive.</li>
+<li>The "-jump-threading" pass is more powerful: it is iterative
+ and handles threading based on values with fully and partially redundant
+ loads.</li>
-<li>The aggressive dead code elimination (ADCE) optimization has been rewritten
-to make it both faster and safer in the presence of code containing infinite
-loops. Some of its prior functionality has been factored out into the loop
-deletion pass, which <em>is</em> safe for infinite loops.</li>
+<li>The "-memdep" memory dependence analysis pass (used by GVN and memcpyopt) is
+ both faster and more aggressive.</li>
+
+<li>The "-scalarrepl" scalar replacement of aggregates pass is more aggressive
+ about promoting unions to registers.</li>
-<li>Several optimizations have been sped up, leading to faster code generation
- with the same code quality.</li>
-
-<li>The 'SimplifyLibCalls' pass, which optimizes calls to libc and libm
- functions for C-based languages, has been rewritten to be a FunctionPass
- instead a ModulePass. This allows it to be run more often and to be
- included at -O1 in llvm-gcc. It was also extended to include more
- optimizations and several corner case bugs were fixed.</li>
-
-<li>LLVM now includes a simple 'Jump Threading' pass, which attempts to simplify
- conditional branches using information about predecessor blocks, simplifying
- the control flow graph. This pass is pretty basic at this point, but
- catches some important cases and provides a foundation to build on.</li>
-
-<li>Several corner case bugs which could lead to deleting volatile memory
- accesses have been fixed.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="codegen">Code Generator Improvements</a>
+<a name="codegen">Target Independent Code Generator Improvements</a>
</div>
<div class="doc_text">
-<p>We put a significant amount of work into the code generator infrastructure,
-which allows us to implement more aggressive algorithms and make it run
-faster:</p>
+<p>We have put a significant amount of work into the code generator
+infrastructure, which allows us to implement more aggressive algorithms and make
+it run faster:</p>
<ul>
-<li>MemOperand in the code generator: describe me!.</li>
+<li>The <a href="WritingAnLLVMBackend.html">Writing an LLVM Compiler
+Backend</a> document has been greatly expanded and is substantially more
+complete.</li>
+
+<li>The SelectionDAG type legalization logic has been completely rewritten, is
+now more powerful (it supports arbitrary precision integer types for example),
+and is more correct in several corner cases. The type legalizer converts
+operations on types that are not natively supported by the target machine into
+equivalent code sequences that only use natively supported types. The old type
+legalizer is still available (for now) and will be used if
+<tt>-disable-legalize-types</tt> is passed to the code generator.
+</li>
-<li>The target-independent code generator infrastructure now uses LLVM's APInt
- class to handle integer values, which allows it to support integer types
- larger than 64 bits. Note that support for such types is also dependent on
- target-specific support. Use of APInt is also a step toward support for
- non-power-of-2 integer sizes.</li>
-
-<li>LLVM 2.3 includes several compile time speedups for code with large basic
- blocks, particular in the instruction selection phase, register allocation,
- scheduling, and tail merging/jump threading.</li>
+<li>The code generator now supports widening illegal vectors to larger legal
+ones (for example, converting operations on <3 x float> to work on
+<4 x float>) which is very important for common graphics
+applications.</li>
-<li>Several improvements which make llc's <tt>--view-sunit-dags</tt>
- visualization of scheduling dependency graphs easier to understand.</li>
-
-<li>The code generator allows targets to write patterns that generate subreg
- references directly in .td files now.</li>
-
-<li><tt>memcpy</tt> lowering in the backend is more aggressive, particularly for
- <tt>memcpy</tt> calls introduced by the code generator when handling
- pass-by-value structure argument copies.</li>
+<li>The assembly printers for each target are now split out into their own
+libraries that are separate from the main code generation logic. This reduces
+the code size of JIT compilers by not requiring them to be linked in.</li>
+
+<li>The 'fast' instruction selection path (used at -O0 and for fast JIT
+ compilers) now supports accelerating codegen for code that uses exception
+ handling constructs.</li>
-<li>Inline assembly with multiple register results now returns those results
- directly in the appropriate registers, rather than going through memory.
- Inline assembly that uses constraints like "ir" with immediates now use the
- 'i' form when possible instead of always loading the value in a register.
- This saves an instruction and reduces register use.</li>
-
-<li>Added support for PIC/GOT style tail calls on x86/32 and initial support
- for tail calls on PowerPC 32 (it may also work on ppc64 but not
- thoroughly tested).</li>
+<li>The optional PBQP register allocator now supports register coalescing.</li>
</ul>
+</div>
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="x86">X86-32 and X86-64 Target Improvements</a>
</div>
+<div class="doc_text">
+<p>New features of the X86 target include:
+</p>
+
+<ul>
+<li>The <tt><a href="LangRef.html#int_returnaddress">llvm.returnaddress</a></tt>
+intrinsic (which is used to implement <tt>__builtin_return_address</tt>) now
+supports non-zero stack depths on X86.</li>
+
+<li>The X86 backend now supports code generation of vector shift operations
+using SSE instructions.</li>
+
+<li>X86-64 code generation now takes advantage of red zone, unless the
+<tt>-mno-red-zone</tt> option is specified.</li>
+
+<li>The X86 backend now supports using address space #256 in LLVM IR as a way of
+performing memory references off the GS segment register. This allows a
+front-end to take advantage of very low-level programming techniques when
+targeting X86 CPUs. See <tt>test/CodeGen/X86/movgs.ll</tt> for a simple
+example.</li>
+
+<li>The X86 backend now supports a <tt>-disable-mmx</tt> command line option to
+ prevent use of MMX even on chips that support it. This is important for cases
+ where code does not contain the proper <tt>llvm.x86.mmx.emms</tt>
+ intrinsics.</li>
+
+<li>The X86 JIT now detects the new Intel <a
+ href="http://en.wikipedia.org/wiki/Intel_Core_i7">Core i7</a> and <a
+ href="http://en.wikipedia.org/wiki/Intel_Atom">Atom</a> chips and
+ auto-configures itself appropriately for the features of these chips.</li>
+
+<li>The JIT now supports exception handling constructs on Linux/X86-64 and
+ Darwin/x86-64.</li>
+
+<li>The JIT supports Thread Local Storage (TLS) on Linux/X86-32 but not yet on
+ X86-64.</li>
+</ul>
+
+</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="x86specific">X86/X86-64 Specific Improvements</a>
+<a name="pic16">PIC16 Target Improvements</a>
</div>
<div class="doc_text">
-<p>New target-specific features include:
+<p>New features of the PIC16 target include:
</p>
<ul>
-<li>llvm-gcc's X86-64 ABI conformance is far improved, particularly in the
- area of passing and returning structures by value. llvm-gcc compiled code
- now interoperates very well on X86-64 systems with other compilers.</li>
+<li>Both direct and indirect load/stores work now.</li>
+<li>Logical, bitwise and conditional operations now work for integer data
+types.</li>
+<li>Function calls involving basic types work now.</li>
+<li>Support for integer arrays.</li>
+<li>The compiler can now emit libcalls for operations not supported by m/c
+instructions.</li>
+<li>Support for both data and ROM address spaces.</li>
+</ul>
+
+<p>Things not yet supported:</p>
+
+<ul>
+<li>Floating point.</li>
+<li>Passing/returning aggregate types to and from functions.</li>
+<li>Variable arguments.</li>
+<li>Indirect function calls.</li>
+<li>Interrupts/programs.</li>
+<li>Debug info.</li>
+</ul>
-<li>Support for Win64 was added. This includes code generation itself, JIT
- support and necessary changes to llvm-gcc.</li>
+</div>
+
+
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="llvmc">Improvements in LLVMC</a>
+</div>
-<li>The LLVM X86 backend now supports the support SSE 4.1 instruction set, and
- the llvm-gcc 4.2 front-end supports the SSE 4.1 compiler builtins. Various
- generic vector operations (insert/extract/shuffle) are much more efficient
- when SSE 4.1 is enabled. The JIT automatically takes advantage of these
- instructions, but llvm-gcc must be explicitly told to use them, e.g. with
- <tt>-march=penryn</tt>.</li>
+<div class="doc_text">
+<p>New features include:</p>
-<li>The X86 backend now does a number of optimizations that aim to avoid
- converting numbers back and forth from SSE registers to the X87 floating
- point stack.</li>
+<ul>
+<li>Beginning with LLVM 2.5, <tt>llvmc2</tt> is known as
+ just <tt>llvmc</tt>. The old <tt>llvmc</tt> driver was removed.</li>
-<li>The X86 backend supports stack realignment, which is particularly useful for
- vector code on OS's without 16-byte aligned stacks.</li>
+<li>The Clang plugin was substantially improved and is now enabled
+ by default. The command <tt>llvmc --clang</tt> can be now used as a
+ synonym to <tt>ccc</tt>.</li>
-<li>The X86 backend now supports the "sseregparm" options in GCC, which allow
- functions to be tagged as passing floating point values in SSE
- registers.</li>
+<li>There is now a <tt>--check-graph</tt> option, which is supposed to catch
+ common errors like multiple default edges, mismatched output/input language
+ names and cycles. In general, these checks can't be done at compile-time
+ because of the need to support plugins.</li>
-<li>Trampolines (taking the address of a nested function) now work on
- Linux/X86-64.</li>
+<li>Plugins are now more flexible and can refer to compilation graph nodes and
+ options defined in other plugins. To manage dependencies, a priority-sorting
+ mechanism was introduced. This change affects the TableGen file syntax. See the
+ documentation for details.</li>
-<li><tt>__builtin_prefetch</tt> is now compiled into the appropriate prefetch
- instructions instead of being ignored.</li>
+<li>Hooks can now be provided with arguments. The syntax is "<tt>$CALL(MyHook,
+ 'Arg1', 'Arg2', 'Arg3')</tt>".</li>
-<li>128-bit integers are now supported on X86-64 targets.</li>
+<li>A new option type: multi-valued option, for options that take more than one
+ argument (for example, "<tt>-foo a b c</tt>").</li>
-<li>The register allocator can now rematerialize PIC-base computations.</li>
+<li>New option properties: '<tt>one_or_more</tt>', '<tt>zero_or_more</tt>',
+'<tt>hidden</tt>' and '<tt>really_hidden</tt>'.</li>
-<li>The "t" and "f" inline assembly constraints for the X87 floating point stack
- now work. However, the "u" constraint is still not fully supported.</li>
+<li>The '<tt>case</tt>' expression gained an '<tt>error</tt>' action and
+ an '<tt>empty</tt>' test (equivalent to "<tt>(not (not_empty ...))</tt>").</li>
+
+<li>Documentation now looks more consistent to the rest of the LLVM
+ docs. There is also a man page now.</li>
</ul>
-
+
</div>
+
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="targetspecific">Other Target Specific Improvements</a>
+<a name="changes">Major Changes and Removed Features</a>
</div>
<div class="doc_text">
-<p>New target-specific features include:
-</p>
+
+<p>If you're already an LLVM user or developer with out-of-tree changes based
+on LLVM 2.4, this section lists some "gotchas" that you may run into upgrading
+from the previous release.</p>
<ul>
-<li>The LLVM C backend now supports vector code.</li>
-</ul>
-
-</div>
+<li>llvm-gcc defaults to <tt>-fno-math-errno</tt> on all X86 targets.</li>
+</ul>
-<!--=========================================================================-->
-<div class="doc_subsection">
-<a name="otherimprovements">Other Improvements</a>
-</div>
-<div class="doc_text">
-<p>New features include:
-</p>
+<p>In addition, many APIs have changed in this release. Some of the major LLVM
+API changes are:</p>
<ul>
-<li>LLVM now builds with GCC 4.3.</li>
-<li>Bugpoint now supports running custom scripts (with the <tt>-run-custom</tt>
- option) to determine how to execute the command and whether it is making
- forward process.</li>
+<li>Some deprecated interfaces to create <tt>Instruction</tt> subclasses, that
+ were spelled with lower case "create," have been removed.</li>
</ul>
-
+
</div>
+
+
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="portability">Portability and Supported Platforms</a>
<p>LLVM is known to work on the following platforms:</p>
<ul>
-<li>Intel and AMD machines (IA32) 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 10.3 and above in 32-bit and
- 64-bit modes.</li>
+<li>Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) 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 10.3 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>
<div class="doc_text">
-<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
+<p>This section contains significant known problems with the LLVM system,
+listed by component. If you run into a problem, please check the <a
href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
there isn't already one.</p>
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
<ul>
-<li>The MSIL, IA64, Alpha, SPU, and MIPS backends are experimental.</li>
-<li>The llc "<tt>-filetype=asm</tt>" (the default) is the only supported
- value for this option.</li>
+<li>The MSIL, IA64, Alpha, SPU, MIPS, and PIC16 backends are experimental.</li>
+<li>The <tt>llc</tt> "<tt>-filetype=asm</tt>" (the default) is the only
+ supported value for this option.</li>
</ul>
</div>
<li>The X86 backend generates inefficient floating point code when configured
to generate code for systems that don't have SSE2.</li>
<li>Win64 code generation wasn't widely tested. Everything should work, but we
- expect small issues to happen. Also, llvm-gcc cannot build mingw64 runtime
- currently due
+ expect small issues to happen. Also, llvm-gcc cannot build the mingw64
+ runtime currently due
to <a href="http://llvm.org/PR2255">several</a>
- <a href="http://llvm.org/PR2257">bugs</a> in FP stackifier
+ <a href="http://llvm.org/PR2257">bugs</a> and due to lack of support for
+ the
+ 'u' inline assembly constraint and for X87 floating point inline assembly.</li>
+ <li>The X86-64 backend does not yet support the LLVM IR instruction
+ <tt>va_arg</tt>. Currently, the llvm-gcc and front-ends support variadic
+ argument constructs on X86-64 by lowering them manually.</li>
</ul>
</div>
<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>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
<div class="doc_text">
<ul>
-<li>The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not
+<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="mips-be">Known problems with the MIPS back-end</a>
+</div>
+
+<div class="doc_text">
+
+<ul>
+<li>The O32 ABI is not fully supported.</li>
+<li>64-bit MIPS targets are not supported yet.</li>
+</ul>
+
+</div>
+
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="alpha-be">Known problems with the Alpha back-end</a>
<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>
+<li>The Itanium backend is highly experimental and has a number of known
+ issues. We are looking for a maintainer for the Itanium backend. If you
+ are interested, please contact the LLVMdev mailing list.</li>
</ul>
</div>
inline assembly code</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>
+ C++ code compiled with <tt>llc</tt> or native compilers.</li>
<li>The C backend does not support all exception handling constructs.</li>
+<li>The C backend does not support arbitrary precision integers.</li>
</ul>
</div>
<a name="c-fe">Known problems with the llvm-gcc C front-end</a>
</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Bugs</div>
-
<div class="doc_text">
<p>llvm-gcc 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>
+LLVMdev mailing list if you are interested.</p>
<p>The only major language feature of GCC not supported by llvm-gcc is
the <tt>__builtin_apply</tt> family of builtins. However, some extensions
itself, Qt, Mozilla, etc.</p>
<ul>
-<li>Exception handling works well on the X86 and PowerPC targets, including
-X86-64 darwin. This works when linking to a libstdc++ compiled by GCC. It is
-supported on X86-64 linux, but that is disabled by default in this release.</li>
+<li>Exception handling works well on the X86 and PowerPC targets. Currently
+ only Linux and Darwin targets are supported (both 32 and 64 bit).</li>
</ul>
</div>
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a>
+</div>
+
+<div class="doc_text">
+<ul>
+<li>Fortran support generally works, but there are still several unresolved bugs
+ in Bugzilla. Please see the tools/gfortran component for details.</li>
+</ul>
+</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
</div>
<div class="doc_text">
-The llvm-gcc 4.2 Ada compiler works fairly well, however this is not a mature
-technology and problems should be expected.
+The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature
+technology, and problems should be expected.
<ul>
<li>The Ada front-end currently only builds on X86-32. This is mainly due
-to lack of trampoline support (pointers to nested functions) on other platforms,
-
however it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>
+to lack of trampoline support (pointers to nested functions) on other platforms.
+
However, it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>
which does support trampolines.</li>
<li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
+This is due to lack of LLVM support for <tt>setjmp</tt>/<tt>longjmp</tt> style
+exception handling, which is used internally by the compiler.
Workaround: configure with --disable-bootstrap.</li>
-<li>The c380004 and <a href="http://llvm.org/PR2010">c393010</a> ACATS tests
-fail (c380004 also fails with gcc-4.2 mainline). When built at -O3, the
-<a href="http://llvm.org/PR2421">cxg2021</a> ACATS test also fails.</li>
-<li>Some gcc specific Ada tests continue to crash the compiler. The testsuite
-reports most tests as having failed even though they pass.</li>
+<li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>
+and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail
+(c380004 also fails with gcc-4.2 mainline).
+If the compiler is built with checks disabled then <a href="http://llvm.org/PR2010">c393010</a>
+causes the compiler to go into an infinite loop, using up all system memory.</li>
+<li>Some GCC specific Ada tests continue to crash the compiler.</li>
<li>The -E binder option (exception backtraces)
<a href="http://llvm.org/PR1982">does not work</a> and will result in programs
crashing if an exception is raised. Workaround: do not use -E.</li>
<hr>
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