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First draft of the llvm 1.8 release notes.

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<head> <head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link rel="stylesheet" href="llvm.css" type="text/css"> <link rel="stylesheet" href="llvm.css" type="text/css">
<title>LLVM 1.7 Release Notes</title> <title>LLVM 1.8 Release Notes</title>
</head> </head>
<body> <body>
<div class="doc_title">LLVM 1.7 Release Notes</div> <div class="doc_title">LLVM 1.8 Release Notes</div>
<ol> <ol>
<li><a href="#intro">Introduction</a></li> <li><a href="#intro">Introduction</a></li>
@ -32,9 +32,10 @@
<div class="doc_text"> <div class="doc_text">
<p>This document contains the release notes for the LLVM compiler <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 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 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 not reading this on the LLVM web pages, you should probably go there because
this document may be updated after the release.</p> 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 <p>This is the eighth public release of the LLVM Compiler Infrastructure. This
release incorporates a large number of enhancements and new features, release incorporates a large number of enhancements and new features,
including vector support (Intel SSE and Altivec), a new GCC4.0-based including DWARF debugging support (C and C++ on Darwin/PPC), improved inline
C/C++ front-end, Objective C/C++ support, inline assembly support, and many assembly support, a new <a href="http://llvm.org/nightlytest/">nightly
other big features. tester</a>, llvm-config enhancments, many bugs
fixed, and performance and compile time improvements.
</p> </p>
</div> </div>
<!--=========================================================================--> <!--=========================================================================-->
<div class="doc_subsection"> <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>
<!--_________________________________________________________________________--> <!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="llvmgcc4">GCC4.0-based llvm-gcc <div class="doc_subsubsection"><a name="dwarf">DWARF debugging
front-end</a></div> support </a></div>
<div class="doc_text"> <div class="doc_text">
<p>LLVM 1.7 includes a brand new llvm-gcc, based on GCC 4.0.1. This version <p>The llvm-gcc4 C front-end now generates debugging info for C and C++. This
of llvm-gcc solves many serious long-standing problems with llvm-gcc, including information is propagated through the compiler and the code generator can
all of those blocked by the <a href="http://llvm.org/PR498">llvm-gcc 4 meta currently produce DWARF debugging information from it. DWARF is a standard
bug</a>. In addition, llvm-gcc4 implements support for many new features, debugging format used on many platforms, but currently LLVM only includes
including GCC inline assembly, generic vector support, SSE and Altivec target support for Mac OS X targets for the 1.8 release.
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> </p>
</div> </div>
@ -104,174 +97,96 @@ Support</a></div>
<div class="doc_text"> <div class="doc_text">
<p>The LLVM IR and llvm-gcc4 front-end now fully support arbitrary GCC <a <p>Inline assembly support is substantially improved in LLVM 1.8 over LLVM 1.7.
href="LangRef.html#inlineasm">inline assembly</a>. The LLVM X86 and PowerPC Many unsupported features are now supported, and inline asm support in the X86
code generators have initial support for it, backend is far better. llvm-gcc4 now supports global register variables as
being able to compile basic statements, but are missing some features. Please well.</p>
report any inline asm statements that crash the compiler or that are miscompiled
as bugs.</p>
</div> </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"> <div class="doc_text">
<p>LLVM 1.7 includes a new, fully functional, SPARC backend built in the <p>The Loop Optimizer pass now used "Loop-Closed SSA Form", which makes it
target-independent code generator. This SPARC backend includes support for easier to update SSA form as loop transformations change the code. An
SPARC V8 and SPARC V9 subtargets (controlling whether V9 features can be used), immediate benefit of this is that the loop unswitching pass can now unswitch
and targets the 32-bit SPARC ABI.</p> loops in more cases.
<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> </p>
</div> </div>
<!--_________________________________________________________________________--> <!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="optimizernew">Optimizer <div class="doc_subsubsection"><a name="jumptab">Jump Table Support for Switches
Improvements</a></div> </a></div>
<div class="doc_text"> <div class="doc_text">
<ul>
<li>The Loop Unswitching pass (<tt>-loop-unswitch</tt>) has had several bugs <p>The code generator now lowers switch statements to jump tables, providing
fixed, has several new features, and is enabled by default in llvmgcc3 significant performance boosts for applications (e.g. interpreters) whose
now.</li> performance is highly correlated to switch statement performance.</p>
<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>
</div> </div>
<!--_________________________________________________________________________--> <!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="codgennew">Code Generator <div class="doc_subsubsection"><a name="jitrelease">Deallocation of JIT'd
Improvements</a></div> Machine Code
</a></div>
<div class="doc_text"> <div class="doc_text">
<ul>
<li>LLVM has a new prepass (before register allocation) list scheduler, which <p>The LLVM JIT now allows clients to deallocate machine code JIT'd to its code
supports bottom-up and top-down scheduling, pluggable priority functions and buffer. This is important for long living applications that depend on the JIT.
pluggable hazard recognizers. The X86 backend uses this to reduce register </p>
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>
</div> </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"> <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> <ul>
<li>The Mac OS/X PowerPC and X86 backends now have initial support for <li>LLVM 1.8 includes an initial ARM backend. This backend is in early
Darwin DWARF development stages.</li>
debugging information, however, debug info generation has been disabled for <li>LLVM 1.8 now includes significantly better support for mingw and
the 1.7 release in llvmgcc4.</li> cygwin.</li>
<li>LLVM includes the new <a href="docs/CommandGuide/html/llvm-config.html"> <li>The <a href="CommandGuide/html/llvm-config.html">llvm-config</a> tool is
llvm-config</a> utility, which makes it easier to build and link programs now built by default and has several new features.</li>
against the LLVM libraries when not using the LLVM makefiles.</li> <li>The X86 and PPC backends now use the correct platform ABI for passing
<li>LLVM now supports first class global ctor/dtor initialization lists, no vectors as arguments to functions.</li>
longer forcing targets to use "__main".</li> <li>The X86 backend now includes support for the Microsoft ML assembler
<li>LLVM supports assigning globals and functions to a particular section ("MASM").</li>
in the result executable using the GCC section attribute.</li> <li>The PowerPC backend now pattern matches the 'rlwimi' instruction more
<li><a href="ExtendingLLVM.html">Adding intrinsics to LLVM</a> is now aggressively.</li>
significantly easier.</li> <li>Most of LLVM is now built with "-pedantic", ensuring better portability
<li>llvmgcc4 now fully supports C99 Variable Length Arrays, including dynamic to more C++ Compilers.</li>
stack deallocation.</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> </ul>
</div> </div>
<!--=========================================================================--> <!--=========================================================================-->
<div class="doc_subsection"> <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>
<div class="doc_text"> <div class="doc_text">
<ul> <ul>
<li>The official LLVM URL is now <a href="http://llvm.org/"> <li>The LLVM "SparcV9" backend (deprecated in LLVM 1.7) has been removed in
http://llvm.org/</a>.</li> LLVM 1.8. The LLVM "Sparc" backend replaces it.</li>
<li>The LLVM intrinsics used to be overloaded based on type: for example, <li>The --version option now prints more useful information, including the
<a href="LangRef.html#int_ctpop"><tt>llvm.ctpop</tt></a> could work with any build configuration for the tool.</li>
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>
</ul> </ul>
</div> </div>
@ -382,8 +297,7 @@ components, please contact us on the llvmdev list.</p>
<div class="doc_text"> <div class="doc_text">
<p> <p>
llvm-gcc3 has many significant problems that are fixed by llvm-gcc4. See llvm-gcc3 has many significant problems that are fixed by llvm-gcc4.
those blocked on the <a href="http://llvm.org/PR498">llvm-gcc4 meta bug</a>.
Two major ones include:</p> Two major ones include:</p>
<ul> <ul>
@ -401,6 +315,11 @@ Two major ones include:</p>
href="http://llvm.org/PR162">with the largest union member</a>.</li> href="http://llvm.org/PR162">with the largest union member</a>.</li>
</ul> </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> </div>
<!-- _______________________________________________________________________ --> <!-- _______________________________________________________________________ -->
@ -638,8 +557,7 @@ space if they depend on these (e.g. C99 varargs).</li>
<div class="doc_text"> <div class="doc_text">
<ul> <ul>
<li><a href="http://llvm.org/PR736">Indirect calls crash JIT on <li>none yet.</li>
Darwin/x86</a>.</li>
</ul> </ul>
</div> </div>
@ -718,19 +636,16 @@ programs.</li>
</div> </div>
<!-- ======================================================================= --> <!-- ======================================================================= -->
<div class="doc_subsection"> <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>
<div class="doc_text"> <div class="doc_text">
<ul> <ul>
<li><a href="http://llvm.org/PR60">[sparcv9] SparcV9 backend miscompiles <li>The ARM backend is currently in early development stages, it is not
several programs in the LLVM test suite</a></li> ready for production use.</li>
<li>The SparcV9 backend is slated to be removed before the LLVM 1.8
release.</li>
</ul> </ul>
</div> </div>