<p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
</div>
-<h1><font color="red">THIS IS A WORK IN PROGRESS FOR THE LLVM 2.2
-RELEASE</font</h1>
<!-- *********************************************************************** -->
<div class="doc_section">
</div>
+<!-- Unfinished features in 2.2:
+ Index Set Splitting not enabled by default
+ Machine LICM
+ Machine Sinking
+ LegalizeDAGTypes
+ -->
+
+<!--=========================================================================-->
+<div class="doc_subsection">
+<a name="deprecation">Deprecated features in LLVM 2.2</a>
+</div>
+
+<div class="doc_text">
+
+<p>This is the last LLVM release to support llvm-gcc 4.0, llvm-upgrade, and
+llvmc in its current form. llvm-gcc 4.0 has been replaced with llvm-gcc 4.2.
+llvm-upgrade is useful for upgrading llvm 1.9 files to llvm 2.x syntax, but you
+can always use an old release to do this. llvmc is currently mostly useless in
+llvm 2.2, and will be redesigned or removed in llvm 2.3.</p>
+
+</div>
+
<!--=========================================================================-->
<div class="doc_subsection">
<a name="frontends">llvm-gcc 4.0, llvm-gcc 4.2, and clang</a>
LLVM 2.1, llvm-gcc 4.2 was beta). Since LLVM 2.1, the llvm-gcc 4.2 front-end
has made leaps and bounds and is now at least as good as 4.0 in virtually every
area, and is better in several areas (for example, exception handling
-correctness). We strongly recommend that you migrate from llvm-gcc 4.0 to
-llvm-gcc 4.2 in this release cycle because <b>LLVM 2.2 is the last release
-that will support llvm-gcc 4.0</b>: LLVM 2.3 will only support the llvm-gcc
-4.2 front-end.</p>
+correctness, support for Ada and FORTRAN). We strongly recommend that you
+migrate from llvm-gcc 4.0 to llvm-gcc 4.2 in this release cycle because
+<b>LLVM 2.2 is the last release that will support llvm-gcc 4.0</b>: LLVM 2.3
+will only support the llvm-gcc 4.2 front-end.</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
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 2.2 release. If you are interested in
-this project, please see the web site.</p>
+this project, please see its <a href="http://clang.llvm.org/">web site</a>.</p>
</div>
<div class="doc_text">
-<p>Dale contributed full support for long double on x86/x86-64 (where it is 80
-bits) and on Darwin PPC/PPC64 (where it is 128 bits).</p>
+<p>LLVM 2.2 includes several major new capabilities:</p>
-<p>Ada, gfortran</p>
+<ul>
+<li>Scott Michel contributed an SPU backend, which generates code for the
+vector coprocessors on the Cell processor. (Status?)</li>
-<p>
-debug improvements -O0
-EH.
+<li>llvm-gcc 4.2 has significantly improved support for the GCC Ada (GNAT) and
+FORTRAN (gfortran) frontends. Duncan has the llvm-gcc 4.2 GNAT front-end
+supporting almost all of the ACATS testsuite (except 2 tests?). The llvm-gcc
+4.2 gfortran front-end supports a broad range of FORTRAN code, but does <a
+href="http://llvm.org/PR1971">not support EQUIVALENCE yet</a>.</li>
-Gordon: GC Revamp. docs/GarbageCollection.html
+<li>Dale contributed full support for long double on x86/x86-64 (where it is 80
+bits) and on Darwin PPC/PPC64 (where it is 128 bits). In previous LLVM
+releases, llvm-gcc silently mapped long double to double.</li>
-Kaleidescope: docs/tutorial
+<li>Gordon Henriksen rewrote most of the <a href="GarbageCollection.html"
+>Accurate Garbage Collection</a> code in the code generator, making the
+generated code more efficient and adding support for the Ocaml garbage collector
+metadata format.</li>
-Gordon: C and Ocaml Bindings
+<li>Christopher Lamb contributed support for multiple address spaces in LLVM
+IR. This is useful for supporting targets that have 'near' vs 'far' pointers,
+'RAM' vs 'ROM' pointers, or that have non-local memory that can be accessed with
+special instructions.</li>
+
+<li>LLVM now includes a new set of detailed <a
+href="tutorial/index.html">tutorials</a>, which explain how to implement a
+language with LLVM and shows how to use several important APIs.</li>
+
+</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="optimizer">Optimizer Improvements</a>
+<a name="coreimprovements">LLVM Core Improvements</a>
</div>
<div class="doc_text">
-
-<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>
+<p>New features include:
+</p>
<ul>
+<li>Gordon contributed support for C and Ocaml Bindings for the basic LLVM IR
+construction routines as well as several other auxiliary APIs.</li>
-<li>Daniel Berlin and (Curtis?) rewrote Andersen's alias analysis (which is not
-enabled by default) to be several orders of magnitude faster, implmented Offline
-Variable Substitution.</li>
+<li>Anton added readnone/readonly attributes for modeling function side effects.
+Duncan hooked up GCC's pure/const attributes to use them and enhanced mod/ref
+analysis to use them.</li>
+<li>Devang added LLVMFoldingBuilder, a version of LLVMBuilder that implicitly
+simplifies the code as it is constructed.</li>
-Devang: LoopIndexSplit is enabled by default.
-</ul>
+<li>Ted Kremenek added a framework for generic object serialization to bitcode
+files. This support is only used by clang right now for ASTs but is extensible
+and could be used for serializing arbitrary other data into bitcode files.</li>
+
+<li>Duncan improved TargetData to distinguish between the size/alignment of a
+type in a register, in memory according to the platform ABI, and in memory when
+we have a choice.</li>
+
+<li>Duncan moved parameter attributes off of FunctionType and onto functions
+and calls. This makes it much easier to add attributes to a function in a
+transformation pass.</li>
+<li>Dan Gohman added support for vector sin, cos, and pow intrinsics.</li>
+
+</ul>
+
</div>
<!--=========================================================================-->
<div class="doc_text">
-<p>foci of this release was performance tuning and bug
- fixing. In addition to these, several new major changes occurred:</p>
+<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>
<ul>
-<li>Owen contributed Machine Loop info, domintors, etc. Merged dom and
- postdom.</li>
+<li>Owen refactored the existing LLVM dominator and loop information code to
+allow it work on the machine code representation. He contributed support for
+dominator and loop information on machine code and merged the code for forward
+and backward dominator computation.</li>
-<li>Dan added support for emitting debug information with .file and .loc on
-targets that support it</li>
+<li>Dan added support for emitting debug information with .file and .loc
+directives on that support it, instead of emitting large tables in the .s
+file.</li>
-<li>Evan physical register dependencies in the BURR scheduler</li>
+<li>Evan extended the DAG scheduler to model physical register dependencies
+explicitly and have the BURR scheduler pick a correct schedule based on the
+dependencies. This reduces our use of the 'flag' operand hack.</li>
-<li>Evan EXTRACT_SUBREG coalescing support</li>
-</ul>
+<li>Evan added initial support for register coalescing of subregister
+references.</li>
-</div>
+<li>Rafael Espindola implemented initial support for a new 'byval' attribute,
+which allows more efficient by-value argument passing in the LLVM IR. Evan
+finished support for it and enabled it in the X86 (32- and 64-bit) and C
+backends.</li>
+<li>The LLVM TargetInstrInfo class can now answer queries about the mod/ref and
+side-effect behavior of MachineInstr's. This information is inferred
+automatically by TableGen from .td files for all instructions with
+patterns.</li>
-<!--=========================================================================-->
-<div class="doc_subsection">
-<a name="targetspecific">Target Specific Improvements</a>
-</div>
+<li>Evan implemented simple live interval splitting on basic block boundaries.
+This allows the register allocator to be more successful at keeping values in
+registers in some parts of a value's live range, even if they need to be spilled
+in some other block.</li>
-<div class="doc_text">
-<p>New features include:
-</p>
+<li>The new MachineRegisterInfo.h class provides support for efficiently
+iterating over all defs/uses of a register, and this information is
+automatically kept up-to-date. This support is similar to the use_iterator in
+the LLVM IR level.</li>
-<ul>
-<li>Evan X86 now models EFLAGS in instructions.</li>
-<li>Evan: If conversion on by default for ARM.</li>
-<li>Bruno: MIPS PIC support.</li>
-<li>Arnold Schwaighofer: X86 tail call support.</li>
+<li>The MachineInstr, MachineOperand and TargetInstrDesc classes are simpler,
+more consistent, and better documented.</li>
</ul>
-
-</div>
+</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="llvmgccimprovements">llvm-gcc Improvements</a>
+<a name="optimizer">Optimizer Improvements</a>
</div>
<div class="doc_text">
-<p>New features include:
-</p>
+
+<p>In addition to a huge array of bug fixes and minor performance tweaks, the
+LLVM 2.2 optimizers support a few major enhancements:</p>
<ul>
-<li>.</li>
+
+<li>Daniel Berlin and Curtis Dunham rewrote Andersen's alias analysis to be
+several orders of magnitude faster, and implemented Offline Variable
+Substitution and Lazy Cycle Detection. Note that Andersen's is not enabled in
+llvm-gcc by default, but can be accessed through 'opt'.</li>
+
+<li>Dan Gohman contributed several enhancements to Loop Strength Reduction (LSR)
+to make it more aggressive with SSE intrinsics.</li>
+
+<li>Evan added support for simple exit value substitution to LSR.</li>
+
+<li>Evan enhanced LSR to support induction variable reuse when the induction
+variables have different widths.</li>
+
</ul>
-
+
</div>
<!--=========================================================================-->
<div class="doc_subsection">
-<a name="coreimprovements">LLVM Core Improvements</a>
+<a name="targetspecific">Target Specific Improvements</a>
</div>
<div class="doc_text">
-<p>New features include:
+<p>New target-specific features include:
</p>
<ul>
-<li>Devang added LLVMFoldingBuilder.</li>
-<li>Dan added support for vector sin, cos, and pow intrinsics.</li>
+<li>Evan contributed support to the X86 backend to model the mod/ref behavior
+of the EFLAGS register explicitly in all instructions. This gives more freedom
+to the scheduler, and is a more explicit way to model the instructions.</li>
+<li>Dale contributed support for exception handling on Darwin/x86-64 and
+Darwin/ppc.</li>
+<li>Evan turned on if-conversion by default for ARM, allowing LLVM to take
+advantage of its predication features.</li>
+<li>Bruno added PIC support to the MIPS backend, fixed many bugs and improved
+support for architecture variants.</li>
+<li>Arnold Schwaighofer added support for X86 tail calls (limitations?
+details?).</li>
+<li>Evan contributed several enhancements to Darwin/x86 debug information,
+and improvements at -O0 (details?).</li>
</ul>
</div>
</p>
<ul>
-<li>.</li>
+<li>Gordon expanded and updated the <a href="Passes.html">LLVM Analysis and
+Transformation Passes</a> reference to include descriptions for each pass.</li>
+
+<li>We rewrote the lexer and parser used by TableGen to make them simpler
+and cleaner. This gives tblgen support for 'caret diagnostics'. The .ll file
+lexer was also rewritten to support caret diagnostics but doesn't use this
+support yet.</li>
+
+<li>Dale has been grinding through the GCC testsuite, and marked many
+LLVM-incompatible tests as not-to-be-run (for example, if they are grepping
+through some GCC dump file that LLVM doesn't produce), he also found and fixed
+many LLVM bugs exposed by the testsuite.</li>
</ul>
</div>
<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>
+<li>The X86 backend generates inefficient floating point code when configured to
+ generate code for systems that don't have SSE2.</li>
</ul>
</div>
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
+<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>
<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>noreturn</tt>, <tt>nothrow</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>
- <b>Ignored:</b> <tt>nothrow</tt>, <tt>malloc</tt>,
+ <b>Ignored:</b> <tt>malloc</tt>,
<tt>no_instrument_function</tt></li>
</ol>
</li>
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