maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

some writing. 

llvm-svn: 145198
This commit is contained in:
Chris Lattner 2011-11-27 21:30:28 +00:00
parent 9661de7d30
commit 644976405f
1 changed files with 57 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

100
llvm/docs/ReleaseNotes.html
View File

@ -753,7 +753,7 @@ be used to verify some algorithms.
llvm/lib/Archive - replace with lib object?
-->
<p>LLVM 3.0 includes several major changes:</p>
<p>LLVM 3.0 includes several major changes and big features:</p>
<ul>
<li>llvm-gcc is no longer supported, and not included in the release. We
@ -767,12 +767,19 @@ be used to verify some algorithms.
href="http://blog.llvm.org/2011/09/greedy-register-allocation-in-llvm-30.html">blog post</a> or its talk at the <a
href="http://llvm.org/devmtg/2011-11/">Developer Meeting</a>
for more information.</li>
<li> New <a href="Atomics.html">atomics</a> instructions, "#i_fence" instruction, cmpxchg, atomicrmw too. What target support (X86/ARM)? Also 'atomic load/store'.
<li>LLVM IR now includes full support for <a href="Atomics.html">atomics
memory operations</a> intended to support the C++'11 and C'1x memory models.
This includes <a href="LangRef.html#memoryops">atomic load and store,
compare and exchange, and read/modify/write instructions</a> as well as a
full set of <a href="LangRef.html#ordering">memory ordering constraints</a>.
Please see the <a href="Atomics.html">Atomics Guide</a> for more
information.
</li>
<li>The LLVM IR exception handling representation has been redesigned and
reimplemented, making it more elegant, fixing a huge number of bugs, and
enabling inlining and other optimizations. Please see its blog post (XXX
not yet) for more information.</li>
not yet) and the <a href="ExceptionHandling.html">Exception Handling
documentation</a> for more information.</li>
<li>The LLVM IR Type system has been redesigned and reimplemented, making it
faster and solving some long-standing problems.
Please see its <a
@ -780,13 +787,14 @@ be used to verify some algorithms.
post</a> for more information.</li>
<li>The MIPS backend has made major leaps in this release, going from an
experimental target to being virtually production quality that supports a
experimental target to being virtually production quality and supporting a
wide variety of MIPS subtargets. See the <a href="#MIPS">MIPS section</a>
below for more information.</li>
<li>The optimizer and code generator now supports gprof and gcov-style coverage
and profiling information, and includes a new llvm-cov tool. Clang exposes
this through GCC-compatible command line options.</li>
and profiling information, and includes a new llvm-cov tool (but also works
with gcov). Clang exposes coverage and profiling through GCC-compatible
command line options.</li>
</ul>
</div>
@ -802,38 +810,28 @@ be used to verify some algorithms.
<p>LLVM IR has several new features for better support of new targets and that
expose new optimization opportunities:</p>
New llvm.expect intrinsic.
New llvm.fma intrinsic.
LangRef.html#fnattrs uwtable attribute for asynch unwind tables.
llvm.prefetch now takes a 4th argument that specifies whether the prefetch happens to the icache or dcache.
New nonlazybind function attribute.
data layout string can encode the natural alignment of the target's stack for better optimization (LangRef.html#datalayout)
returns_twice attribute (rafael)
</div>
<!--=========================================================================-->
<h3>
<a name="loopoptimization">Loop Optimization Improvements</a>
</h3>
<div>
<p>The induction variable simplification pass in 3.0 only modifies
induction variables when profitable. Sign and zero extension
elimination, linear function test replacement, loop unrolling, and
other simplifications that require induction variable analysis have
been generalized so they no longer require loops to be rewritten in a
typically suboptimal form prior to optimization. This new design
preserves more IR level information, avoids undoing earlier loop
optimizations (particularly hand-optimized loops), and no longer
strongly depends on the code generator rewriting loops a second time
in a now optimal form--an intractable problem.</p>
<p>The original behavior can be restored with -mllvm -enable-iv-rewrite;
however, support for this mode will be short lived. As such, bug
reports should be filed for any significant performance regressions
when moving from -mllvm -enable-iv-rewrite to the 3.0 default mode.</p>
<ul>
<li><a href="Atomics.html">Atomic memory accesses and memory ordering</a> are
now directly expressible in the IR.</li>
<li>A new <a href="LangRef.html#int_fma">llvm.fma intrinsic</a> directly
represents floating point multiply accumulate operations without an
intermediate rounding stage.</li>
<li>A new llvm.expect intrinsic (XXX not documented in langref) allows a
frontend to express expected control flow (and the __builtin_expect builtin
from GNU C).</li>
<li>The <a href="LangRef.html#int_prefetch">llvm.prefetch intrinsic</a> now
takes a 4th argument that specifies whether the prefetch happens from the
icache or dcache.</li>
<li>The new <a href="LangRef.html#uwtable">uwtable function attribute</a>
allows a frontend to control emission of unwind tables.</li>
<li>The new <a href="LangRef.html#fnattrs">nonlazybind function
attribute</a> allow optimization of Global Offset Table (GOT) accesses.</li>
<li>The new <a href="LangRef.html#returns_twice">returns_twice attribute</a>
allows better modeling of functions like setjmp.</li>
<li>The <a href="LangRef.html#datalayout">target datalayout</a> string can now
encode the natural alignment of the target's stack for better optimization.
</li>
</ul>
</div>
<!--=========================================================================-->
@ -843,12 +841,14 @@ be used to verify some algorithms.
<div>
<p>In addition to a large array of minor performance tweaks and bug fixes, this
<p>In addition to many minor performance tweaks and bug fixes, this
release includes a few major enhancements and additions to the
optimizers:</p>
<ul>
Pass manager extension API.
<li>The pass manager now has an extension API that allows front-ends and plugins
to insert their own optimizations in the well-known places in the standard
pass optimization pipeline.</li>
<li>Information about <a href="BranchWeightMetadata.html">branch probability</a>
and basic block frequency is now available within LLVM, based on a
@ -857,10 +857,24 @@ be used to verify some algorithms.
register spill placement and if-conversion, with additional optimizations
planned for future releases. The same framework is intended for eventual
use with profile-guided optimization.</li>
ARC language specific optimizer (Transforms/ObjCARC) a decent example of language-specific transformation.
<li>The "-indvars" induction variable simplification pass only modifies
induction variables when profitable. Sign and zero extension
elimination, linear function test replacement, loop unrolling, and
other simplifications that require induction variable analysis have
been generalized so they no longer require loops to be rewritten into
canonical form prior to optimization. This new design
preserves more IR level information, avoids undoing earlier loop
optimizations (particularly hand-optimized loops), and no longer
requires the code generator to reconstruct loops into an optimal form -
an intractable problem.</li>
<li>LLVM now includes a pass to optimize retain/release calls for the
<a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html">Automatic
Reference Counting</a> (ARC) Objective-C language feature (in
lib/Transforms/ObjCARC). It is a decent example of implementing a
source-language-specific optimization in LLVM.</li>
</ul>
</div>