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rip out llvm 2.4 details to make room for 2.5

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@ -4,11 +4,11 @@
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link rel="stylesheet" href="llvm.css" type="text/css">
<title>LLVM 2.4 Release Notes</title>
<title>LLVM 2.5 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 2.4 Release Notes</div>
<div class="doc_title">LLVM 2.5 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
@ -33,7 +33,7 @@
<div class="doc_text">
<p>This document contains the release notes for the LLVM Compiler
Infrastructure, release 2.4. Here we describe the status of LLVM, including
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>
@ -51,7 +51,7 @@ current one. To see the release notes for a specific release, please see the
</div>
<!-- Unfinished features in 2.4:
<!-- Unfinished features in 2.5:
Machine LICM
Machine Sinking
LegalizeDAGTypes
@ -72,7 +72,7 @@ current one. To see the release notes for a specific release, please see the
<div class="doc_text">
<p>
The LLVM 2.4 distribution currently consists of code from the core LLVM
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
@ -170,21 +170,13 @@ 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>Following LLVM 2.4, VMKit has its first release 0.24 that you can find on its
<p>Following LLVM 2.5, VMKit has its first release 0.24 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> Support for generics in the .Net virtual machine.</li>
<li> Initial support for the Mono class libraries. </li>
<li> Support for MacOSX/x86, following LLVM's support for exceptions in
JIT on MacOSX/x86. </li>
<li> A new vmkit driver: a program to run java or .net applications. The driver
supports llvm command line arguments including the new "-fast" option. </li>
<li> A new memory allocation scheme in the JVM that makes unloading a
class loader very fast. </li>
<li> VMKit now follows the LLVM Makefile machinery. </li>
<li>?</li>
</ul>
</div>
@ -211,29 +203,10 @@ in this section.
<div class="doc_text">
<p>LLVM 2.4 includes several major new capabilities:</p>
<p>LLVM 2.5 includes several major new capabilities:</p>
<ul>
<li><p>The most visible end-user change in LLVM 2.4 is that it includes many
optimizations and changes to make -O0 compile times much faster. You should see
improvements in speed on the order of 30% (or more) than in LLVM 2.3. There are
many pieces to this change described in more detail below. The speedups and new
components can also be used for JIT compilers that want fast
compilation.</p></li>
<li><p>The biggest change to the LLVM IR is that Multiple Return Values (which
were introduced in LLVM 2.3) have been generalized to full support for "First
Class Aggregate" values in LLVM 2.4. This means that LLVM IR supports using
structs and arrays as values in a function. This capability is mostly useful
for front-end authors, who prefer to treat things like complex numbers, simple
tuples, dope vectors, etc., as Value*'s instead of as a tuple of Value*'s or as
memory values. Bitcode files from LLVM 2.3 will automatically migrate to the
general representation.</p></li>
<li><p>LLVM 2.4 also includes an initial port for the PIC16 microprocessor. This
target only has support for 8 bit registers, and a number of other crazy
constraints. While the port is still in early development stages, it shows some
interesting things you can do with LLVM.</p></li>
<li><p>?</p></li>
</ul>
@ -252,29 +225,7 @@ 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>
<ul>
<li>LLVM 2.4 supports the full set of atomic <tt>__sync_*</tt> builtins. LLVM
2.3 only supported those used by OpenMP, but 2.4 supports them all. Note that
while llvm-gcc supports all of these builtins, not all targets do. X86 support
them all in both 32-bit and 64-bit mode and PowerPC supports them all except for
the 64-bit operations when in 32-bit mode.</li>
<li>llvm-gcc now supports an <tt>-flimited-precision</tt> option, which tells
the compiler that it is okay to use low-precision approximations of certain libm
functions (like <tt>exp</tt>, <tt>log</tt>, etc). This allows you to get high
performance if you only need (say) 12-bits of precision.</li>
<li>llvm-gcc now supports a C language extension known as "<a
href="http://lists.cs.uiuc.edu/pipermail/cfe-dev/2008-August/002670.html">Blocks</a>".
This feature is similar to nested functions and closures, but does not
require stack trampolines (with most ABIs), and supports returning closures
from functions that define them. Note that actually <em>using</em> Blocks
requires a small runtime that is not included with llvm-gcc.</li>
<li>llvm-gcc now supports a new <tt>-flto</tt> option. On systems that support
transparent Link Time Optimization (currently Darwin systems with Xcode 3.1 and
later) this allows the use of LTO with other optimization levels like -Os.
Previously, LTO could only be used with -O4, which implied optimizations in
-O3 that can increase code size.</li>
<li>?</li>
</ul>
</div>
@ -289,43 +240,7 @@ Previously, LTO could only be used with -O4, which implied optimizations in
<p>New features include:</p>
<ul>
<li>A major change to the <tt>Use</tt> class landed, which shrank it by 25%. Since
this is a pervasive part of the LLVM, it ended up reducing the memory use of
LLVM IR in general by 15% for most programs.</li>
<li>Values with no names are now pretty printed by <tt>llvm-dis</tt> more
nicely. They now print as "<tt>%3 = add i32 %A, 4</tt>" instead of
"<tt>add i32 %A, 4 ; &lt;i32&gt;:3</tt>", which makes it much easier to read.
</li>
<li>LLVM 2.4 includes some changes for better vector support. First, the shift
operations (<tt>shl</tt>, <tt>ashr</tt>, and <tt>lshr</tt>) now all support
vectors and do an element-by-element shift (shifts of the whole vector can be
accomplished by bitcasting the vector to <tt>&lt;1 x i128&gt;</tt>, for example). Second,
there is initial support in development for vector comparisons with the
<tt><a href="LangRef.html#i_fcmp">fcmp</a>/<a href="LangRef.html#i_icmp">icmp</a></tt>
instructions. These instructions compare two vectors and return a vector of
<tt>i1</tt>'s for each result. Note that there is very little codegen support
available for any of these IR features though.</li>
<li>A new <tt>DebugInfoBuilder</tt> class is available, which makes it much
easier for front-ends to create debug info descriptors, similar to the way that
<tt>IRBuilder</tt> makes it easier to create LLVM IR.</li>
<li>The <tt>IRBuilder</tt> class is now parameterized by a class responsible
for constant folding. The default <tt>ConstantFolder</tt> class does target independent
constant folding. The <tt>NoFolder</tt> class does no constant folding at all, which is
useful when learning how LLVM works. The <tt>TargetFolder</tt> class folds the most,
doing target dependent constant folding.</li>
<li>LLVM now supports "function attributes", which allow us to separate return
value attributes from function attributes. LLVM now supports attributes on a
function itself, a return value, and its parameters. New supported function
attributes include <tt>noinline/alwaysinline</tt> and the <tt>opt-size</tt> flag,
which says the function should be optimized for code size.</li>
<li>LLVM IR now directly represents "common" linkage, instead of
representing it as a form of weak linkage.</li>
<li>?</li>
</ul>
@ -343,39 +258,7 @@ release includes a few major enhancements and additions to the optimizers:</p>
<ul>
<li>The Global Value Numbering (GVN) pass now does local Partial Redundancy
Elimination (PRE) to eliminate some partially redundant expressions in cases
where doing so won't grow code size.</li>
<li>LLVM 2.4 includes a new loop deletion pass (which removes output-free
provably-finite loops) and a rewritten Aggressive Dead Code Elimination (ADCE)
pass that no longer uses control dependence information. These changes speed up
the optimizer and also prevent it from deleting output-free infinite
loops.</li>
<li>The new AddReadAttrs pass works out which functions are read-only or
read-none (these correspond to 'pure' and 'const' in GCC) and marks them
with the appropriate attribute.</li>
<li>LLVM 2.4 now includes a new SparsePropagation framework, which makes it
trivial to build lattice-based dataflow solvers that operate over LLVM IR. Using
this interface means that you just define objects to represent your lattice
values and the transfer functions that operate on them. It handles the
mechanics of worklist processing, liveness tracking, handling PHI nodes,
etc.</li>
<li>The Loop Strength Reduction and induction variable optimization passes have
several improvements to avoid inserting MAX expressions, to optimize simple
floating point induction variables and to analyze trip counts of more
loops.</li>
<li>Various helper functions (ComputeMaskedBits, ComputeNumSignBits, etc) were
pulled out of the Instruction Combining pass and put into a new
<tt>ValueTracking.h</tt> header, where they can be reused by other passes.</li>
<li>The tail duplication pass has been removed from the standard optimizer
sequence used by llvm-gcc. This pass still exists, but the benefits it once
provided are now achieved by other passes.</li>
<li>?</li>
</ul>
@ -393,41 +276,7 @@ which allows us to implement more aggressive algorithms and make it run
faster:</p>
<ul>
<li>The target-independent code generator supports (and the X86 backend
currently implements) a new interface for "fast" instruction selection. This
interface is optimized to produce code as quickly as possible, sacrificing
code quality to do it. This is used by default at -O0 or when using
"llc -fast" on X86. It is straight-forward to add support for
other targets if faster -O0 compilation is desired.</li>
<li>In addition to the new 'fast' instruction selection path, many existing
pieces of the code generator have been optimized in significant ways.
SelectionDAG's are now pool allocated and use better algorithms in many
places, the ".s" file printers now use <tt>raw_ostream</tt> to emit text much faster,
etc. The end result of these improvements is that the compiler also takes
substantially less time to generate code that is just as good (and often
better) than before.</li>
<li>Each target has been split to separate the ".s" file printing logic from the
rest of the target. This enables JIT compilers that don't link in the
(somewhat large) code and data tables used for printing a ".s" file.</li>
<li>The code generator now includes a "stack slot coloring" pass, which packs
together individual spilled values into common stack slots. This reduces
the size of stack frames with many spills, which tends to increase L1 cache
effectiveness.</li>
<li>Various pieces of the register allocator (e.g. the coalescer and two-address
operation elimination pass) now know how to rematerialize trivial operations
to avoid copies and include several other optimizations.</li>
<li>The <a href="CodeGenerator.html#selectiondag_process">graphs</a> produced by
the <tt>llc -view-*-dags</tt> options are now significantly prettier and
easier to read.</li>
<li>LLVM 2.4 includes a new register allocator based on Partitioned Boolean
Quadratic Programming (PBQP). This register allocator is still in
development, but is very simple and clean.</li>
<li>?</li>
</ul>
@ -444,17 +293,7 @@ faster:</p>
</p>
<ul>
<li>Exception handling is supported by default on Linux/x86-64.</li>
<li>Position Independent Code (PIC) is now supported on Linux/x86-64.</li>
<li><tt>@llvm.frameaddress</tt> now supports getting the frame address of stack frames
&gt; 0 on x86/x86-64.</li>
<li>MIPS has improved a lot since last release, the most important changes
are: Little endian support, floating point support, allegrex core and
intrinsics support. O32 ABI is improved but isn't complete. The EABI
was implemented and is fully supported. We also have support for small
sections and gp_rel relocation for its access, a threshold in bytes can be
specified through command line.</li>
<li>The PowerPC backend now supports trampolines.</li>
<li>?</li>
</ul>
</div>
@ -470,21 +309,7 @@ faster:</p>
</p>
<ul>
<li><tt>llvmc2</tt> (the generic compiler driver) gained plugin
support. It is now easier to experiment with <tt>llvmc2</tt> and
build your own tools based on it.</li>
<li>LLVM 2.4 includes a number of new generic algorithms and data structures,
including a scoped hash table, 'immutable' data structures, a simple
free-list manager, and a <tt>raw_ostream</tt> class.
The <tt>raw_ostream</tt> class and
<tt>format</tt> allow for efficient file output, and various pieces of LLVM
have switched over to use it. The eventual goal is to eliminate
use of <tt>std::ostream</tt> in favor of it.</li>
<li>LLVM 2.4 includes an optional build system based on CMake. It
still is in its early stages but can be useful for Visual C++
users who can not use the Visual Studio IDE.</li>
<li>?</li>
</ul>
@ -498,19 +323,12 @@ faster:</p>
<div class="doc_text">
<p>If you're already an LLVM user or developer with out-of-tree changes based
on LLVM 2.3, this section lists some "gotchas" that you may run into upgrading
on LLVM 2.4, this section lists some "gotchas" that you may run into upgrading
from the previous release.</p>
<ul>
<li>The LLVM IR generated by llvm-gcc no longer names all instructions. This
makes it run faster, but may be more confusing to some people. If you
prefer to have names, the '<tt>opt -instnamer</tt>' pass will add names to
all instructions.</li>
<li>The LoadVN and GCSE passes have been removed from the tree. They are
obsolete and have been replaced with the GVN and MemoryDependence passes.
</li>
<li>?</li>
</ul>
@ -518,51 +336,10 @@ from the previous release.</p>
API changes are:</p>
<ul>
<li>Now, function attributes and return value attributes are managed
separately. Interface exported by <tt>ParameterAttributes.h</tt> header is now
exported by <tt>Attributes.h</tt> header. The new attributes interface changes are:
<ul>
<li><tt>getParamAttrs</tt> method is now replaced by
<tt>getParamAttributes</tt>, <tt>getRetAttributes</tt> and
<tt>getFnAttributes</tt> methods.</li>
<li> Return value attributes are stored at index 0. Function attributes are
stored at index ~0U. Parameter attributes are stored at index that matches
parameter number.</li>
<li> <tt>ParamAttr</tt> namespace is now renamed as <tt>Attribute</tt>.</li>
<li> The name of the class that manages reference count of opaque
attributes is changed from <tt>PAListPtr</tt> to <tt>AttrListPtr</tt>.</li>
<li> <tt>ParamAttrsWithIndex</tt> is now renamed as <tt>AttributeWithIndex</tt>.
</li>
<li>?</li>
</ul>
</li>
<li>The <tt>DbgStopPointInst</tt> methods <tt>getDirectory</tt> and
<tt>getFileName</tt> now return <tt>Value*</tt> instead of strings. These can be
converted to strings using <tt>llvm::GetConstantStringInfo</tt> defined via
"<tt>llvm/Analysis/ValueTracking.h</tt>".</li>
<li>The APIs to create various instructions have changed from lower case
"create" methods to upper case "Create" methods (e.g.
<tt>BinaryOperator::create</tt>). LLVM 2.4 includes both cases, but the
lower case ones are removed in mainline (2.5 and later), please migrate.</li>
<li>Various header files like "<tt>llvm/ADT/iterator</tt>" were given a ".h" suffix.
Change your code to #include "<tt>llvm/ADT/iterator.h</tt>" instead.</li>
<li>The <tt>getresult</tt> instruction has been removed and replaced with the
<tt>extractvalue</tt> instruction. This is part of support for first class
aggregates.</li>
<li>In the code generator, many <tt>MachineOperand</tt> predicates were renamed to be
shorter (e.g. <tt>isFrameIndex()</tt> -&gt; <tt>isFI()</tt>),
<tt>SDOperand</tt> was renamed to <tt>SDValue</tt> (and the "<tt>Val</tt>"
member was changed to be the <tt>getNode()</tt> accessor), and the
<tt>MVT::ValueType</tt> enum has been replaced with an "<tt>MVT</tt>"
struct. The <tt>getSignExtended</tt> and <tt>getValue</tt> methods in the
ConstantSDNode class were renamed to <tt>getSExtValue</tt> and
<tt>getZExtValue</tt> respectively, to be more consistent with
the <tt>ConstantInt</tt> class.</li>
<li>?</li>
</ul>
</div>