[LLVMdev] LLVM Weekly - #74, Jun 1st 2015

[Alex Bradbury]

LLVM Weekly - #74, Jun 1st 2015
===============================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/74>

Welcome to the seventy-fourth 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.

You may be interested in the [second RISC-V
workshop](https://blog.riscv.org/2015/04/registration-now-open-2nd-risc-v-workshop-june-29-30-2015/),
which will be held in Berkeley June 29-30. Early bird registration ends today,
but academics can register for free. My colleague Wei and I will be there
representing [lowRISC](http://www.lowrisc.org).


## News and articles from around the web

[MPI-Checker](https://github.com/0ax1/MPI-Checker), a static analysis tool for
MPI code has been released. It is of course implemented using Clang's [Static
Analyzer framework](http://clang-analyzer.llvm.org/).

The LLVM-HPC2 workshop will be held on November 15th, co-located with SC15.
The [call for
papers](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86349) has
been published. Submissions are due by September 1st.


## On the mailing lists

* The discussion about improving LLD has resumed. Rui Ueyama has [written
about his recent patch for a section-based PE/COFF
linker](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86306). Sean
Silva argues that [refactoring might be a better
approach](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86333).

* Hans Wennborg has shared a [preliminary release plan for LLVM/Clang
3.7](http://article.gmane.org/gmane.comp.compilers.clang.devel/42972). This
would see the codebase branched on the 14th of July with a release target of
the end of August. Tom Stellard has also shared a [schedule for the 3.6.2
release](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86175). The
deadline for patches is June 15 with the release date targeted for June 29th.

* Teresa Johnson has posted an [updated RFC of her ThinLTO implementation
plan](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86282). There
are still concerns about the wrapping of LLVM bitcode in ELF. Alex Rosenberg
suggests [implementing an objcopy replacement for LLVM and extending bitcode
as necessary](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86313)
as an alternative approach.

* Chris Bieneman has posted a [status update on the quest to replace the
autoconf build system with
CMake](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86248).

* Quentin Colombet is [seeking benchmark
reports](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86222) (or
indeed bugs!) for the recently added 'shrink wrapping'.

* Matthias Braun has left a quick note for maintainers of out-of-tree targets
that [pristine register semantics have been modified
slightly](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86291).

* Chandler Carruth has posted some thoughts on [next steps for loop unrolling
analysis](http://article.gmane.org/gmane.comp.compilers.llvm.devel/86137).


## LLVM commits

* Codegen for memcpy on Thumb2 has been improved to make use of load/store
multiple (more details of how this works in the commit message, worth a read
for those interested). [r238473](http://reviews.llvm.org/rL238473).

* Popcount on x86 will now be implemented using a [lookup table in register
technique](http://wm.ite.pl/articles/sse-popcount.html).
[r238636](http://reviews.llvm.org/rL238636),
[r238652](http://reviews.llvm.org/rL238652).

* Work continues on reducing peak memory usage through optimisations to debug
info. [r238364](http://reviews.llvm.org/rL238364).

* Initial support for the `convergent` attribute has landed.
[r238264](http://reviews.llvm.org/rL238264).

* The documentation about the current state of LLVM's Phabricator has been
updated along with a call for volunteers to help develop necessary
improvements and modifications to Phabricator's PHP codebase.
[r238295](http://reviews.llvm.org/rL238295).

* MCJIT gained support for MIPS64r2 and MIPS64r6.
[r238424](http://reviews.llvm.org/rL238424).


## Clang commits

* Clang's handling of `-fopenmp` has been rewritten.
[r238389](http://reviews.llvm.org/rL235111).

* The user documentation on profiling has been extended.
[r238504](http://reviews.llvm.org/rL238504).


## Other project commits

* A new PE/COFF section-based linker has been added to lld. This follows on
from discussions about the direction of lld and whether it makes sense to
build on top of the atom model. The linker is able to self-link on Windows and
is significantly faster than the current implementations (1.2 seconds vs 5
seconds, even without multi-threading). It also takes only 250MB of RAM to
self-link vs 2GB. [r238458](http://reviews.llvm.org/rL238458).

* LLDB on Windows can now demangle Linux or Android symbols.
[r238460](http://reviews.llvm.org/rL238460).