[LLVMdev] LLVM Weekly - #73, May 25th 2015

[Alex Bradbury]

LLVM Weekly - #73, May 25th 2015
================================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/73>.

Welcome to the seventy-third 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.


## News and articles from around the web

The LLVM blog has properly
[announced](http://blog.llvm.org/2015/05/openmp-support_22.html) full support
for OpenMP 3.1 in Clang.

The Clang-derived [Zapcc](http://www.zapcc.com/) has had [some
attention](https://news.ycombinator.com/item?id=9592601) this week. It claims
higher compilation speeds than the baseline Clang or other compilers. Yaron
Keren, the principal developer has shared [many more details about its
implementation](http://article.gmane.org/gmane.comp.compilers.clang.devel/42950)
on the Clang mailing list.


## On the mailing lists

* The discussion about upstreaming the LLVM/SPIR-V converter has continued.
Chandler Carruth has [responded with
feedback](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86000), and
Philip Reames has [shared his
concerns](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86054)
about the merge proposal as-is. Neil Henning has [responded to some of these
concerns](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86056).

* Adam Nemet has kicked off a thread about [alias-based loop
versioning](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86024),
with the hope that others working in the area can chime in.

* Félix Cloutier queries why [MemoryDependencyAnalysis reports dependencies
between NoAlias
pointers](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86029).
Daniel Berlin points to his very interesting looking work on
[MemorySSA](http://reviews.llvm.org/D7864).

* Duncan P.N. Exon Smith has posted an RFC on [reducing the memory footprint
of debug info
entries](http://article.gmane.org/gmane.comp.compilers.llvm.devel/85981). The
attached patches reduce peak memory usage from 920MB to 884MB for the tested
workload.

* John Criswell has a helpful answer regarding [how to determine whether a
branch instruction may depend on function
parameters](http://article.gmane.org/gmane.comp.compilers.llvm.devel/85987).

* Andrew Kaylor has shared a [detailed description of the work to be done for
exception handling on
Windows](http://article.gmane.org/gmane.comp.compilers.llvm.devel/85926).

* Andrew Bokhanko is looking for feedback on [adding an option to control a
level of OpenMP support in
Clang](http://article.gmane.org/gmane.comp.compilers.clang.devel/42622). Now
that 3.1 support is complete, OpenMP 4.0 is the next target but this is likely
to remain incomplete for some time. The question is whether those features
which are implemented are available by default, or whether users should opt-in
with a compiler flag while support remains incomplete.


## LLVM commits

* The `dereferenceable_or_null` attribute will now be exploited by the loop
environment code motion pass. [r237593](http://reviews.llvm.org/rL237593).

* Commits have started on the 'MIR serialization' project, which aims to print
machine functions in a readable format.
[r237954](http://reviews.llvm.org/rL237954).

* A GCStrategy for CoreCLR has been committed alongside some documentation for
it. [r237753](http://reviews.llvm.org/rL237753),
[r237869](http://reviews.llvm.org/rL237869).

* libFuzzer gained some more documentation.
[r237836](http://reviews.llvm.org/rL237836).

* libFuzzer can now be used with user-supplied mutators.
[r238059](http://reviews.llvm.org/rL238059),
[r238062](http://reviews.llvm.org/rL238062).


## Clang commits

* `-fopenmp` will turn on OpenMP support and link with libiomp5 (libgomp can
alternatively be specified). [r237769](http://reviews.llvm.org/rL237769).

* The `-mrecip` flag has been added to match GCC.
[r238055](http://reviews.llvm.org/rL238055).


## Other project commits

* C++1z status for libcxx has been updated.
[r237606](http://reviews.llvm.org/rL237606).

* `std::bool_constant` and `uninitialized_copy()` was added to libcxx.
[r237636](http://reviews.llvm.org/rL237636),
[r237699](http://reviews.llvm.org/rL237699).

* libcxx gained a TODO list. Plenty of tasks that might be interesting to new
contributors. [r237813](http://reviews.llvm.org/rL237813),
[r237988](http://reviews.llvm.org/rL237988).

* LDB has enabled debugging of multithreaded programs on Windows and gained
support for attaching to process. [r237637](http://reviews.llvm.org/rL237637),
[r237817](http://reviews.llvm.org/rL237817).