<div class="doc_text">
-<p>Some of the most noticable improvements this release have been in the
-optimizer, speeding it up and making it more aggressive</p>
+<p>Some of the most noticable feature improvements this release have been in the
+optimizer, speeding it up and making it more aggressive. For example:</p>
<ul>
<li>Owen Anderson wrote the new MemoryDependenceAnalysis pass, which provides
- a lazy, caching layer on top of alias analysis. He then used it to rewrite
+ a lazy, caching layer on top of <a href="AliasAnalysis.html">
+ AliasAnalysis</a>. He then used it to rewrite
DeadStoreElimination which resulted in significantly better compile time in
common cases, </li>
<li>Owen implemented the new GVN pass, which is also based on
shares some details with the new GVN pass. It is still in need of compile
time tuning, and is not turned on by default.</li>
<li>Devang merged ETForest and DomTree into a single easier to use data
-structure.</li>
+ structure. This makes it more obvious which datastructure to choose
+ (because there is only one) and makes the compiler more memory and time
+ efficient (less stuff to keep up-to-date).</li>
<li>Nick Lewycky improved loop trip count analysis to handle many more common
-cases.</li>
+ cases.</li>
</ul>
<div class="doc_text">
+<p>One of the main focuses of this release was performance tuning and bug
+ fixing. In addition to these, several new major changes occurred:</p>
+
<ul>
-<li>Dale finished up the Tail Merging optimization in the code generator,
-enabling it by default. This produces smaller code that is also faster in some
-cases.</li>
+<li>Dale finished up the Tail Merging optimization in the code generator, and
+ enabled it by default. This produces smaller code that is also faster in
+ some cases.</li>
+
+<li>Christopher Lamb implemented support for virtual register sub-registers,
+ which can be used to better model many forms of subregisters. As an example
+ use, he modified the X86 backend to use this to model truncates and
+ extends more accurately (leading to better code).</li>
<li>Dan Gohman changed the way we represent vectors before legalization,
-significantly simplifying the SelectionDAG representation for these and making
-the code generator faster for vector code.</li>
+ significantly simplifying the SelectionDAG representation for these and
+ making the code generator faster for vector code.</li>
-<li>Evan remat rewrite (coalesced intervals + folding of remat'd loads) and
-live intervals improvements.</li>
+<li>Evan contributed a new target independent if-converter. While it is
+ target independent, at this point only the ARM backend uses it so far.</li>
-<li>Dan Gohman contributed support for better alignment and volatility handling
-in the code generator, and significantly enhanced alignment analysis for SSE
-load/store instructions.</li>
+<li>Evan rewrite the way the register allocator handles rematerialization,
+ allowing it to be much more effective on two-address targets like X86,
+ and taught it to fold loads away when possible (also a big win on X86).</li>
-<li>Christopher Lamb virtual register sub-register support, better truncates and
-extends on X86.</li>
+<li>Dan Gohman contributed support for better alignment and volatility handling
+ in the code generator, and significantly enhanced alignment analysis for SSE
+ load/store instructions. With his changes, an insufficiently-aligned SSE
+ load instruction turns into <tt>movups</tt>, for example.</li>
<li>Duraid Madina contributed a new "bigblock" register allocator, and Roman
-Levenstein contributed several big improvements. BigBlock is optimized for code
-that uses very large basic blocks. It is slightly slower than the "local"
-allocator, but produces much better code.</li>
+ Levenstein contributed several big improvements. BigBlock is optimized for
+ code that uses very large basic blocks. It is slightly slower than the
+ "local" allocator, but produces much better code.</li>
<li>David Greene refactored the register allocator to split coalescing out from
-allocation, making coalescers pluggable.</li>
+ allocation, making coalescers pluggable.</li>
</ul>
</p>
<ul>
-<li>Bruno Cardoso Lopes contributed initial MIPS support.</li>
-<li>Bill Wendling added SSSE3 support.</li>
-<li>New Target independent if converter, ARM uses it so far</li>
+<li>Bruno Cardoso Lopes contributed initial MIPS support. It is sufficient to
+ run many small programs, but is still incomplete and is not yet
+ fully performant.</li>
+
+<li>Bill Wendling added SSSE3 support to the X86 backend.</li>
+
<li>Nicholas Geoffray contributed improved linux/ppc ABI and JIT support.</li>
+
<li>Dale Johannesen rewrote handling of 32-bit float values in the X86 backend
-when using the floating point stack, fixing several nasty bugs.</li>
-<li>Dan contributed rematerialization support for the X86 backend.</li>
+ when using the floating point stack, fixing several nasty bugs.</li>
+
+<li>Dan contributed rematerialization support for the X86 backend, in addition
+ to several X86-specific micro optimizations.</li>
</ul>
</div>
</p>
<ul>
-<li>Duncan and Anton exception handling in llvm-gcc 4.0/4.2</li>
+<li>Duncan and Anton made significant progress chasing down a number of problems
+ with C++ Zero-Cost exception handling in llvm-gcc 4.0 and 4.2. It is now at
+ the point where it "just works" on linux/x86-32 and has partial support on
+ other targets.</li>
-<li>Devang and Duncan: Bitfields, pragma pack</li>
+<li>Devang and Duncan fixed a huge number of bugs relating to bitfields, pragma
+ pack, and variable sized fields in structures.</li>
-<li>Tanya implemented support for __attribute__((noinline)) in llvm-gcc, and
-added support for generic variable annotations which are propagated into the
-LLVM IR, e.g. "<tt>int X __attribute__((annotate("myproperty")));</tt>".</li>
+<li>Tanya implemented support for <tt>__attribute__((noinline))</tt> in
+ llvm-gcc, and added support for generic variable annotations which are
+ propagated into the LLVM IR, e.g.
+ "<tt>int X __attribute__((annotate("myproperty")));</tt>".</li>
<li>Sheng Zhou and Christopher Lamb implemented alias analysis support for
-'restrict' arguments to functions.</li>
+"restrict" pointer arguments to functions.</li>
-<li>Duncan contributed support for trampolines (pointers to nested functions),
-currently only supported on x86 target.</li>
+<li>Duncan contributed support for trampolines (taking the address of a nested
+ functions), currently this is only supported in the x86 target.</li>
-<li> Lauro Ramos Venancio contributed support to encode alignment info in
-load and store instructions.</li>
+<li>Lauro Ramos Venancio contributed support to encode alignment info in
+ load and store instructions, the foundation for other alignment-related
+ work.</li>
</ul>
</div>
</p>
<ul>
-<li>Neil Booth APFloat, foundation for long double support that will be wrapped
-up in 2.2. Dale contributed most of long double support, will be enabled in
-2.2.</li>
+<li>Neil Booth contributed a new "APFloat" class, which ensures that floating
+ point representation and constant folding is not dependent on the host
+ architecture that builds the application. This support is the foundation
+ for "long double" support that will be wrapped up in LLVM 2.2.</li>
+
+<li>Based on the APFloat class, Dale redesigned the internals of the ConstantFP
+ class and has been working on extending the core and optimizer components to
+ support various target-specific 'long double's. We expect this work to be
+ completed in LLVM 2.2.</li>
-<li>LLVM now provides an LLVMBuilder class which makes it significantly easier
-to create LLVM IR instructions.</li>
+<li>LLVM now provides an LLVMBuilder class, which makes it significantly easier
+ to create LLVM IR instructions.</li>
<li>Reid contributed support for intrinsics that take arbitrary integer typed
-arguments, Dan Gohman and Chandler extended it to support FP and vectors.</li>
+ arguments. Dan Gohman and Chandler extended it to support arbitrary
+ floating point arguments and vectors.</li>
</ul>
</div>
</p>
<ul>
-<li>BrainF frontend by Sterling Stein.</li>
+<li>Sterling Stein contributed a new BrainF frontend, located in llvm/examples.
+ This shows a some of the more modern APIs for building a front-end, and
+ demonstrates JIT compiler support.</li>
-<li>David Green contributed a new --enable-expensive-checks configure option
-which enables STL checking, and fixed several bugs exposed by it.</li>
+<li>David Green contributed a new <tt>--enable-expensive-checks</tt> configure
+ option which enables STL checking, and fixed several bugs exposed by
+ it.</li>
</ul>
</div>