diff options
Diffstat (limited to 'docs/ReleaseNotes.html')
| -rw-r--r-- | docs/ReleaseNotes.html | 100 |
1 files changed, 57 insertions, 43 deletions
diff --git a/docs/ReleaseNotes.html b/docs/ReleaseNotes.html index d756fb3..ad4c142 100644 --- a/docs/ReleaseNotes.html +++ b/docs/ReleaseNotes.html @@ -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> |