[LLVMdev] LLVM Weekly - #25, Jun 23rd 2014

[Alex Bradbury]

LLVM Weekly - #25, Jun 23rd 2014
===============================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/25>

Welcome to the twenty-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.


## News and articles from around the web

Facebook have released a number of clang plugins they have been using
internally. This includes plugins to the clang analyzer primarily for iOS
development as well as a plugin to export the Clang AST to JSON. The code is
[available on Github](https://github.com/facebook/facebook-clang-plugins) and
they have started a [discussion on the mailing
list](http://article.gmane.org/gmane.comp.compilers.clang.devel/37318) about
moving some of this code upstream.

This week saw the
[release](http://lists.cs.uiuc.edu/pipermail/llvm-announce/2014-June/000053.html)
of LLVM and Clang 3.4.2. This is a bug-fix release which maintains ABI and API
compatibility with 3.4.1.

Clang's C++ status page [now lists C++1z feature
status](http://clang.llvm.org/cxx_status.html#cxx17).


## On the mailing lists

* Rafael Espíndola has started a thread to discuss [clarification on the
backward compatibility promises of
LLVM](http://article.gmane.org/gmane.comp.compilers.llvm.devel/73948). He
summarises what seems to be the current policy (old .bc is upgraded upon read,
there is no strong guarantee on .ll compatibility). Much of the subsequent
discussion is about issues such as compatibility with metadata format changes.

* Duncan P.N. Exon Smith has posted a [review of the new pass
manager](http://article.gmane.org/gmane.comp.compilers.llvm.devel/73968) in
its current form. He starts with a high-level overview of what Chandler
Carruth's new PassManager infrastructure offers and has a list of queries and
concerns. There are no responses yet, but it's worth keeping your eyes on this
thread if you're interested in LLVM internals development.

* This week has brought two separate proposals for LLVM code coverage support
(neither of which have any replies at the time of writing). Christian Holler
has [proposed inclusion of LLCov
code](http://article.gmane.org/gmane.comp.compilers.llvm.devel/73919). This is
a module pass that instruments basic blocks with calls to functions that will
track coverage. The current LLCov code is [available on
Github](https://github.com/choller/LLCov). Alex L has also posted a [detailed
proposal on improving code coverage support for Clang and
LLVM](http://article.gmane.org/gmane.comp.compilers.clang.devel/37289). He is
looking for feedback on the approach before starting to submit patches.


## LLVM commits

* The LLVM global lock is dead, and the LLVM Programmer's Manual has been
updated to reflect this. `llvm_start_multithreaded` and
`llvm_stop_multithreaded` have been removed.
[r211277](http://reviews.llvm.org/rL211277),
[r211287](http://reviews.llvm.org/rL211287).

* The patchset to improve MergeFunctions performance from O(NxN) to O(N x
log(N)) has finally been completely merged.
[r211437](http://reviews.llvm.org/rL211437),
[r211445](http://reviews.llvm.org/rL211445) and more.

* Range metadata can now be attached to call and invoke (previously it could
only be attached to load). [r211281](http://reviews.llvm.org/rL211281).

* ConvertUTF in the Support library was modified to find the maximal supart of
an ill-formed UTF-8 sequence. [r211015](http://reviews.llvm.org/rL211015).

* LoopUnrollPass will now respect loop unrolling hints in metadata.
[r211076](http://reviews.llvm.org/rL211076).

* The R600 backend has been updated to make use of LDS (Local Data Share) and
vectors for private memory. [r211110](http://reviews.llvm.org/rL211110).

* X86FastISel continues to improve with optimisation for predicates, cmp
folding, and support for 64-bit absolute relocations.
[r211126](http://reviews.llvm.org/rL211126),
[r211130](http://reviews.llvm.org/rL211130).

* The SLPVectorizer (superword-level parallelism) will now recognize and
vectorize non-SIMD instruction patterns like sequences of fadd,fsub or
add,sub. These will be vectorizes as vector shuffles if they are profitable.
[r211339](http://reviews.llvm.org/rL211339).

* LLVM can now generate native unwind info on Win64.
[r211399](http://reviews.llvm.org/rL211399).


## Clang commits

* Clang's OpenMP implementation now contains initial support of the
'reduction' clause, `#pragma omp for`, the 'schedule' clause, the 'ordered'
clause, and the 'nowait' clause. [r211007](http://reviews.llvm.org/rL211007),
[r211140](http://reviews.llvm.org/rL211140),
[r211342](http://reviews.llvm.org/rL211342),
[r211347](http://reviews.llvm.org/rL211347),
[r211352](http://reviews.llvm.org/rL211352).

* MS ABI support continues with the merging of support for x86-64 RTTI.
[r211041](http://reviews.llvm.org/rL211041).

* The `-std=c+++1z` flag was added to enable support for C++17 features.
[r211030](http://reviews.llvm.org/rL211030).

* The clang User's Manual has been expanded with documentation for
profile-guided optimisation with instrumentation.
[r211085](http://reviews.llvm.org/rL211085).

* Emission of ARM NEON intrinsics has been totally rewritten to be easier to
read and maintain as well as to provide better protection against coding
errors. [r211101](http://reviews.llvm.org/rL211101).


## Other project commits

* compiler-rt now offers add, sub, and mul for IEEE quad precision floating
point. [r211312](http://reviews.llvm.org/rL211312),
[r211313](http://reviews.llvm.org/rL211313).