[LLVMdev] LLVM Weekly - #52, Dec 29th 2014

Alex Bradbury asb at asbradbury.org
Mon Dec 29 02:02:19 PST 2014

LLVM Weekly - #52, Dec 29th 2014

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Welcome to the fifty-second 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.

This issue marks the end of one full year of LLVM Weekly. It's a little
shorter than usual as the frenetic pace of LLVM/Clang development has slowed
over the holiday period. Surprising even to me is that we managed to make it
all 52 weeks with an issue every Monday as promised. This requires a
non-trivial amount of time each week (2-3+ hours), but I am intending to keep
it going into 2015. I'd like to give a big thank you to everyone who's said hi
at a conference, sent in corrections or tips on content, or just sent a random
thank you. It's been very helpful in motivation. I don't currently intend to
change anything about the structure or content of each issue for next year,
but if you have any ideas then please let me know.

I can't make it to 31C3 due to the awkward timing of the event, but do let me
know if there are any LLVM/Clang related talks worth sharing. There was a
[talk about Code Pointer
which has previously been covered in LLVM Weekly and is working towards
upstreaming. The video is [here](http://streaming.media.ccc.de/relive/6050).
If you're interested in [lowRISC](http://www.lowrisc.org) and at 31C3, Bunnie
is leading a
[discussion about
at 2pm on Monday (today).

## News and articles from around the web

There doesn't seem to have been any LLVM or Clang related news over the past
week. Everyone seems to be busy with non-LLVM related activities over the
christmas break. If you're looking for a job though, Codeplay tell me they
have two vancancies: one for a [debugger
and another for a
[compiler engineer](https://www.codeplay.com/company/jobs/view.html?uid=12#.VJft7_84JA).

## On the mailing lists

* David Li has shared some [early info on Google's plans for
LTO](http://article.gmane.org/gmane.comp.compilers.llvm.devel/80167). He
describes the concept of 'peak optimization performance' and some of the
objectives of the new design. This includes the ability to handle programs 10x
or 100x the size of Firefox. We can expect more information in 2015, maybe as
early as January.

* The discussion on possible approaches to reducing the size of libLLVM has
continued. Chris Bieneman has [shared some more size
stats](http://article.gmane.org/gmane.comp.compilers.llvm.devel/80096). These
gains come from removing unused intrinsics. Chandler Carruth has followed up
with a pleasingly thought-provoking argument on a different approach:
[target-specific intrinsics shouldn't exist in the LLVM front or
He describes the obvious issues with this, with the most fiddly probably being
instruction selection converting appropriate IR to the right target-specific

## LLVM commits

* The SROA (scalar replacement of aggregates) pass has seen some refactoring
to, in the future, allow for more intelligent rewriting.

* The masked load and store intrinsics have been documented.

* CodeGenPrepare learned to speculate calls to llvm.cttz/ctlz (count
trailing/leading zeroes) if `isCheapToSpeculateCtlz/isCheapToSpeculatCttz` in
TargetLowering return true. [r224899](http://reviews.llvm.org/rL224899).

## Clang commits

* The Clang internals manual has been extended with stub sections on Parse,
Sema, and CodeGen. [r224894](http://reviews.llvm.org/rL224894).

## Other project commits

* The libcxx LIT test-suite has seen a number of new configuration options.
Even better, these are [now documented](http://libcxx.llvm.org/lit_usage.html).

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