[llvm-dev] LLVM Weekly - #105, Jan 4th 2016

[Alex Bradbury via llvm-dev]

LLVM Weekly - #105, Jan 4th 2016
================================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/105>.

Welcome to the one hundred and fifth 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.

Happy new year! This issue marks the second anniversary of LLVM Weekly. It's
rather short as the past week has been very quiet, with most LLVM developers
seemingly taking a break over the holidays. My colleague Wei Song and myself
will be presenting about [lowRISC](http://www.lowrisc.org) at the [3rd RISC-V
workshop](http://riscv.org/workshop-jan2016.html) on Wednesday this week. Do
say hi if you're going to be there.


## News and articles from around the web

Sanjoy Das has written a blog post about [issues with LLVM's undef
value](http://www.playingwithpointers.com/problem-with-undef.html).
Interestingly, he provides an example where undef can actually inhibit
optimisations.


## On the mailing lists

* Devin Coughlin provided a really useful and detailed [guide to how you might
implement a lifetime checker in the Clang static
analyzer](http://lists.llvm.org/pipermail/cfe-dev/2015-December/046653.html).

* There's been some questions raised about [what happened to the LLVM/Clang
3.7.1
release](http://lists.llvm.org/pipermail/llvm-dev/2015-December/093544.html).
Everything is ready to go, it's just waiting for the release manager to push
the button.

* Rahman Lavaee Mashhadi has been [experimenting with disabling function
alignment](http://lists.llvm.org/pipermail/llvm-dev/2015-December/093537.html).
He observes this results in a segfault on some programs, which David Chisnall
points out [is because of the C++ ABI using low-bits on
pointers](http://lists.llvm.org/pipermail/llvm-dev/2015-December/093545.html).

* Dan Liew has posted some [feedback on the Arcanist/Phabricator
work-flow](http://lists.llvm.org/pipermail/llvm-dev/2015-December/093540.html).
This has resulted in a new patch up for review [improving the LLVM Phabricator
documentation](http://reviews.llvm.org/D15801).


## LLVM commits

* The `-align-all-loops` and `-align-all-functions` arguments have been
introduced to force function or loop alignments for testing purposes.
[r256571](http://reviews.llvm.org/rL256571).

* The x86 backend has added intrinsics for reading and writing to the flags
register. [r256685](http://reviews.llvm.org/rL256685).


## Clang commits

* Various Clang classes have been converted to use the TrailingObjects helper.
[r256658](http://reviews.llvm.org/rL256658),
[r256659](http://reviews.llvm.org/rL256659), and more.

* `__readeflags` and `__writeeflags` intrinsics are exposed in Clang.
[r256686](http://reviews.llvm.org/rL256686).


## Other project commits

* In libcxx, undefined behaviour in `<list>` has been fixed for builtin
pointer types and support added for the next ABI version.
[r256652](http://reviews.llvm.org/rL256652).