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First draft of the llvm 1.8 release notes.

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<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link rel="stylesheet" href="llvm.css" type="text/css">
<title>LLVM 1.7 Release Notes</title>
<title>LLVM 1.8 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 1.7 Release Notes</div>
<div class="doc_title">LLVM 1.8 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
@ -32,9 +32,10 @@
<div class="doc_text">
<p>This document contains the release notes for the LLVM compiler
infrastructure, release 1.7. Here we describe the status of LLVM, including any
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 can be found on the <a
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>
@ -62,38 +63,30 @@ href="http://llvm.org/releases/">releases page</a>.</p>
<p>This is the eighth public release of the LLVM Compiler Infrastructure. This
release incorporates a large number of enhancements and new features,
including vector support (Intel SSE and Altivec), a new GCC4.0-based
C/C++ front-end, Objective C/C++ support, inline assembly support, and many
other big 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 enhancments, many bugs
fixed, and performance and compile time improvements.
</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="newfeatures">New Features in LLVM 1.7</a>
<a name="newfeatures">New Features in LLVM 1.8</a>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="llvmgcc4">GCC4.0-based llvm-gcc
front-end</a></div>
<div class="doc_subsubsection"><a name="dwarf">DWARF debugging
support </a></div>
<div class="doc_text">
<p>LLVM 1.7 includes a brand new llvm-gcc, based on GCC 4.0.1. This version
of llvm-gcc solves many serious long-standing problems with llvm-gcc, including
all of those blocked by the <a href="http://llvm.org/PR498">llvm-gcc 4 meta
bug</a>. In addition, llvm-gcc4 implements support for many new features,
including GCC inline assembly, generic vector support, SSE and Altivec
intrinsics, and several new GCC attributes. Finally, llvm-gcc4 is
significantly faster than llvm-gcc3, respects -O options, its -c/-S options
correspond to GCC's (they emit native code), supports Objective C/C++, and
it has debugging support well underway.</p>
<p>If you can use it, llvm-gcc4 offers significant new functionality, and we
hope that it will replace llvm-gcc3 completely in a future release.
Unfortunately, it does not currently support C++ exception handling at all, and
it only works on Apple Mac OS/X machines with X86 or PowerPC processors.
<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>
</div>
@ -104,174 +97,96 @@ Support</a></div>
<div class="doc_text">
<p>The LLVM IR and llvm-gcc4 front-end now fully support arbitrary GCC <a
href="LangRef.html#inlineasm">inline assembly</a>. The LLVM X86 and PowerPC
code generators have initial support for it,
being able to compile basic statements, but are missing some features. Please
report any inline asm statements that crash the compiler or that are miscompiled
as bugs.</p>
<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>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="newsparc">New SPARC backend</a></div>
<div class="doc_subsubsection"><a name="loopopt">Loop Optimizer Improvements</a></div>
<div class="doc_text">
<p>LLVM 1.7 includes a new, fully functional, SPARC backend built in the
target-independent code generator. This SPARC backend includes support for
SPARC V8 and SPARC V9 subtargets (controlling whether V9 features can be used),
and targets the 32-bit SPARC ABI.</p>
<p>The LLVM 1.7 release is the last release that will include the LLVM "SparcV9"
backend, which was the very first LLVM native code generator. It will
be removed in LLVM 1.8, being replaced with the new SPARC backend.</p>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="genvector">Generic Vector Support
</a></div>
<div class="doc_text">
<p>LLVM now includes significantly extended support for SIMD vectors in its
core instruction set. It now includes three new instructions for manipulating
vectors: <a href="LangRef.html#i_extractelement"><tt>extractelement</tt></a>,
<a href="LangRef.html#i_insertelement"><tt>insertelement</tt></a>, and
<a href="LangRef.html#i_shufflevector"><tt>shufflevector</tt></a>. Further,
many bugs in vector handling have been fixed, and vectors are now supported by
the target-independent code generator. For example, if a vector operation is
not supported by a particular target, it will be correctly broken down and
executed as scalar operations.</p>
<p>Because llvm-gcc3 does not support GCC generic vectors or vector intrinsics,
llvm-gcc4 must be used.</p>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="ssealtivec">Intel SSE and PowerPC
Altivec support
</a></div>
<div class="doc_text">
<p>The LLVM X86 backend now supports Intel SSE 1, 2, and 3, and now uses scalar
SSE operations to implement scalar floating point math when the target supports
SSE1 (for floats) or SSE2 (for doubles). Vector SSE instructions are generated
by llvm-gcc4 when the generic vector mechanism or specific SSE intrinsics are
used.
</p>
<p>The LLVM PowerPC backend now supports the Altivec instruction set, including
both GCC -maltivec and -faltivec modes. Altivec instructions are generated
by llvm-gcc4 when the generic vector mechanism or specific Altivec intrinsics
are used.
<p>The Loop Optimizer pass now used "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>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="optimizernew">Optimizer
Improvements</a></div>
<div class="doc_subsubsection"><a name="jumptab">Jump Table Support for Switches
</a></div>
<div class="doc_text">
<ul>
<li>The Loop Unswitching pass (<tt>-loop-unswitch</tt>) has had several bugs
fixed, has several new features, and is enabled by default in llvmgcc3
now.</li>
<li>The Loop Strength Reduction pass (<tt>-loop-reduce</tt>) is now enabled for
the X86 and Alpha backends.</li>
<li>The Instruction Combining pass (<tt>-instcombine</tt>) now includes a
framework and implementation for simplifying code based on whether computed
bits are demanded or not.</li>
<li>The Scalar Replacement of Aggregates pass (<tt>-scalarrepl</tt>) can now
promote simple unions to registers.</li>
<li>The Reassociation pass (<tt>-reassociate</tt>) can now
factor expressions, e.g. turning "A*A+A*B" into "A*(A+B)".</li>
<li>Several LLVM passes are <a href="http://llvm.org/PR681">significantly
faster</a>.</li>
</ul>
<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>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="codgennew">Code Generator
Improvements</a></div>
<div class="doc_subsubsection"><a name="jitrelease">Deallocation of JIT'd
Machine Code
</a></div>
<div class="doc_text">
<ul>
<li>LLVM has a new prepass (before register allocation) list scheduler, which
supports bottom-up and top-down scheduling, pluggable priority functions and
pluggable hazard recognizers. The X86 backend uses this to reduce register
pressure and RISC targets schedule based on operation latency.</li>
<li>The tblgen-based target description framework introduced in LLVM 1.6 has
several new features, useful for targets that can fold loads and stores into
operations, and features that make the .td files more expressive.</li>
<li>The instruction selector is significantly faster in 1.7 than in 1.6.</li>
<li>The X86, Alpha and Itanium backends use new DAG-DAG instruction selectors,
making them easier to maintain and generate slightly better code.</li>
<li>The X86 backend now supports generation of Scalar SSE code for scalar FP
expressions. LLVM provides significantly better performance with Scalar SSE
instructions than it does with the Intel floating point stack
instructions.</li>
<li>The Itanium backend now has a bundling pass, which improves performance
by ~10% and reduces code size (previously it unconditionally inserted a stop
bit after every instruction).</li>
</ul>
<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>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="othernew">Other New Features</a></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>More specific changes include:</p>
<ul>
<li>The Mac OS/X PowerPC and X86 backends now have initial support for
Darwin DWARF
debugging information, however, debug info generation has been disabled for
the 1.7 release in llvmgcc4.</li>
<li>LLVM includes the new <a href="docs/CommandGuide/html/llvm-config.html">
llvm-config</a> utility, which makes it easier to build and link programs
against the LLVM libraries when not using the LLVM makefiles.</li>
<li>LLVM now supports first class global ctor/dtor initialization lists, no
longer forcing targets to use "__main".</li>
<li>LLVM supports assigning globals and functions to a particular section
in the result executable using the GCC section attribute.</li>
<li><a href="ExtendingLLVM.html">Adding intrinsics to LLVM</a> is now
significantly easier.</li>
<li>llvmgcc4 now fully supports C99 Variable Length Arrays, including dynamic
stack deallocation.</li>
<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>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="changes">Significant Changes in LLVM 1.7</a>
<a name="changes">Significant Changes in LLVM 1.8</a>
</div>
<div class="doc_text">
<ul>
<li>The official LLVM URL is now <a href="http://llvm.org/">
http://llvm.org/</a>.</li>
<li>The LLVM intrinsics used to be overloaded based on type: for example,
<a href="LangRef.html#int_ctpop"><tt>llvm.ctpop</tt></a> could work with any
integer datatype. They are now separated into different intrinsics with
suffixes to denote their argument type (e.g. <tt>llvm.ctpop.i32</tt>)). Old
LLVM .ll and .bc files that use these intrinsics will continue to work with
new LLVM versions (they are transparently upgraded by the parsers), but will
cause a warning to be emitted.</li>
<li>The <tt>llvm.readport</tt>, <tt>llvm.writeport</tt>, <tt>llvm.readio</tt>,
and <tt>llvm.writeio</tt> intrinsics have been removed. The first two
were ever only supported by the X86 backend, the last two were never
correctly supported by any target, and none were accessible through the
C front-end. Inline assembly support can now be used to
implement these operations.</li>
<li>The <tt>llvm-db</tt> tool had basic support for stepping through code, which
used the JIT. This code has been removed, and DWARF emission support added
instead. <tt>llvm-db</tt> still exists in CVS if someone wanted to write a
<tt>ptrace</tt> backend for it.</li>
<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>
</ul>
</div>
@ -382,8 +297,7 @@ components, please contact us on the llvmdev list.</p>
<div class="doc_text">
<p>
llvm-gcc3 has many significant problems that are fixed by llvm-gcc4. See
those blocked on the <a href="http://llvm.org/PR498">llvm-gcc4 meta bug</a>.
llvm-gcc3 has many significant problems that are fixed by llvm-gcc4.
Two major ones include:</p>
<ul>
@ -401,6 +315,11 @@ Two major ones include:</p>
href="http://llvm.org/PR162">with the largest union member</a>.</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>
<!-- _______________________________________________________________________ -->
@ -638,8 +557,7 @@ space if they depend on these (e.g. C99 varargs).</li>
<div class="doc_text">
<ul>
<li><a href="http://llvm.org/PR736">Indirect calls crash JIT on
Darwin/x86</a>.</li>
<li>none yet.</li>
</ul>
</div>
@ -718,19 +636,16 @@ programs.</li>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="sparcv9-be">Known problems with the SparcV9 back-end</a>
<a name="arm-be">Known problems with the ARM back-end</a>
</div>
<div class="doc_text">
<ul>
<li><a href="http://llvm.org/PR60">[sparcv9] SparcV9 backend miscompiles
several programs in the LLVM test suite</a></li>
<li>The SparcV9 backend is slated to be removed before the LLVM 1.8
release.</li>
<li>The ARM backend is currently in early development stages, it is not
ready for production use.</li>
</ul>
</div>