[LLVMdev] LLVM Weekly - #51, Dec 22nd 2014

[Alex Bradbury]

LLVM Weekly - #51, Dec 22nd 2014
================================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/51>.

Welcome to the fifty-first issue of LLVM Weekly, a weekly newsletter
(published every Monday) covering developments in LLVM, Clang, and related
projects. LLVM Weekly is brought to you by [Alex
Bradbury](http://asbradbury.org). Subscribe to future issues at
<http://llvmweekly.org> and pass it on to anyone else you think may be
interested. Please send any tips or feedback to <asb at asbradbury.org>, or
@llvmweekly or @asbradbury on Twitter.

Last week as part of the [lowRISC project](http://www.lowrisc.org/) I was
involved in [sharing our plans for tagged memory and 'minion'
cores](http://www.lowrisc.org/docs/memo-2014-001-tagged-memory-and-minion-cores/)
in the initial version. We've almost made it a full year of LLVM Weekly with
no interruption of service!

## News and articles from around the web

3.5.1-rc2 [has been
tagged](http://article.gmane.org/gmane.comp.compilers.llvm.devel/80017), time
to get testing again.

Version 0.15.1 of LDC, the LLVM D Compiler [has been
released](http://forum.dlang.org/thread/zpjjzbkwlisjemoxutms@forum.dlang.org).
The most prominent feature is probably the addition of preliminary support for
MSVC on Win64.

SN Systems (part of Sony) have written a blog post [describing their recently
contributed ABI test
suite](http://www.snsystems.com/technology/2014/12/18/abi-bugs-are-a-nightmare/).

Peter Wilmott has [benchmarked Ruby across various GCC and Clang
releases](https://p8952.info/ruby/2014/12/12/benchmarking-ruby-with-gcc-and-clang.html).
The [discussion at HN](https://news.ycombinator.com/item?id=8762654) may be of
interest.


## On the mailing lists

* Elena Demikhovsky has posted a [proposal for indexed load and store
intrinsics](http://article.gmane.org/gmane.comp.compilers.llvm.devel/79936).
These are intended for AVX-512 or AVX2 gather/scatter instructions which allow
read/write access to multiple memory addresses.

* Chad Rosier kicked off a discussion on [lowering switch statements in the
presence of data from profile guided
optimisation](http://article.gmane.org/gmane.comp.compilers.llvm.devel/79849).
There's some quite detailed discussion about when to use a Huffman tree vs a
jump table.

* Andrew Kaylor has posted [his impression of what needs to be done for MSVC
exception handling
support](http://article.gmane.org/gmane.comp.compilers.llvm.devel/79965). Reid
Kleckner's
[response](http://article.gmane.org/gmane.comp.compilers.llvm.devel/79997) is
informative.

* Ulrich Weigand is [taking over ownership of the SystemZ
port](http://article.gmane.org/gmane.comp.compilers.llvm.devel/79912).

* LLVM/Clang 3.6 is expected to branch in January. Marshall Clow has shared a
[summary of the timings of releases over the past few
years](http://article.gmane.org/gmane.comp.compilers.clang.devel/40292).

* Sean Silva has shared some [thorough notes on the use of standard deviation
and benchmarking in
general](http://article.gmane.org/gmane.comp.compilers.llvm.devel/79962).

## LLVM commits

* Metadata is now typeless in assembly.
[r224257](http://reviews.llvm.org/rL224257).

* PowerPC instruction selection for bit-permuting operations has been
improved. [r224318](http://reviews.llvm.org/rL224318).

* An optimisation has been added to move sign/zero extends close to loads
which causes performance improvements of 2-3% on a few benchmarks on x86.
[r224351](http://reviews.llvm.org/rL224351).

* More overflow arithmetic intrinsics are strength reduced into regular
arithmetic operations if possible.
[r224417](http://reviews.llvm.org/rL224417).



## Clang commits

* Codegen for 'omp for' has started to be committed.
[r224233](http://reviews.llvm.org/rL224233).

* `-save-temps` will now emit unoptimized bitcode files.
[r224688](http://reviews.llvm.org/rL224688).


## Other project commits

* The libcxx test suite can be run with ccache now.
[r224603](http://reviews.llvm.org/rL224603).

* Breakpoints can now be tagged with a name in lldb.
[r224392](http://reviews.llvm.org/rL224392).