[LLVMdev] LLVM Weekly - #5, Feb 3rd 2014

[Alex Bradbury]

LLVM Weekly - #5, Feb 3rd 2014
==============================

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Welcome to the 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. I've been
keeping the [@llvmweekly Twitter account](https://twitter.com/llvmweekly)
updated throughout the week, so follow that if you want more frequent news
updates.

I'm afraid my summary of mailing list activities is much less thorough than
usual, as I've been rather busy this weekend both moving house and suffering
from a cold. Do ping me if you think I've missed anything important.

## News and articles from around the web

This weekend there was an LLVM devroom at FOSDEM 2014. Slides have [already
been posted](http://llvm.org/devmtg/2014-02/) for some of the talks. Hopefully
videos will follow.

Pocl (Portable Computing Language) 0.9 has been
[released](http://portablecl.org/pocl-0.9.html). Pocl aims to be an efficient
MIT-licensed implementation of the OpenCL 1.2 standard.

Mike Ash has published a useful [introduction to
libclang](https://mikeash.com/pyblog/friday-qa-2014-01-24-introduction-to-libclang.html).

Ever wanted to use LLVM from within Rust? This [blog post will tell you
how](http://hydrocodedesign.com/2014/01/31/llvm-with-rust/).

Phoronix has published a [benchmark of Clang 3.4 vs GCC 4.9.0 20140126 on AMD
Kaveri](http://www.phoronix.com/scan.php?page=article&item=amd_kaveri_gcc49clang34&num=1).

## On the mailing lists

* A question about the status of [SEH support in
LLVM/Clang](http://article.gmane.org/gmane.comp.compilers.clang.devel/34747)
was quickly derailed after the expiration of a key patent on SEH in June was
brought up. The conversation moved to LLVM's [developer policy on
patents](http://llvm.org/docs/DeveloperPolicy.html#patents) and whether the
LLVM or Clang mailing lists are a suitable place for their discussion. In the
end, Chris Lattner [chimes in to clarify the
policy](http://article.gmane.org/gmane.comp.compilers.clang.devel/34810). The
technical discussion [moved to this
thread](http://article.gmane.org/gmane.comp.compilers.llvm.devel/69945).

* Pekka Jääskeläinen answers a bugpoint question with a [useful guide on using
bugpoint with a custom exec-command
option](http://article.gmane.org/gmane.comp.compilers.llvm.devel/69807).

* Nick Lewcky suggests [making datalayout a mandatory part of an LLVM
module](http://article.gmane.org/gmane.comp.compilers.llvm.devel/69890).

* Chandler Carruth has proposed in an RFC that [BlockFrequency is the wrong
metric](http://article.gmane.org/gmane.comp.compilers.llvm.devel/70027) for
profile info.

* Sara Elshobaky asks for advice on finding the [number of instructions
executed when running LLVM bytecode under
lli](http://article.gmane.org/gmane.comp.compilers.llvm.devel/69797). There
are a number of suggestions including callgrind, Pin, and other similar tools.

* Markus Timpl raises an interesting question about [describing a load
instruction that changes the value of two
registers](http://article.gmane.org/gmane.comp.compilers.llvm.devel/69852).

* Baoshan Pang writes to the LLVM list asking [how to start getting involved
in LLVM](http://article.gmane.org/gmane.comp.compilers.llvm.devel/69973). If
you've emailed me suggesting you'd like more pointers on how to get stuck in
to LLVM, this thread is for you.

## LLVM commits

* The ARM exception handling ABI
([EHABI](http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038a/IHI0038A_ehabi.pdf))
is now enabled by default.
[r200388](http://llvm-reviews.chandlerc.com/rL200388).

* TargetLowering gained a hook which targets can implement to indicate whether
a load of a constant should be converted to just the constant.
[r200271](http://llvm-reviews.chandlerc.com/rL200271).

* Line table debug info is now supported for COFF files when targeting win32.
[r200340](http://llvm-reviews.chandlerc.com/rL200340).

* LLVM now has the beginnings of a line editor library, initially to be used
by clang-query but possibly consumed by LLDB as well in the future.
[r200595](http://llvm-reviews.chandlerc.com/rL200595).

* The R600 backend learned intrinsics for `S_SENDMSG` and `BUFFER_LOAD_DWORD*`
instructions. [r200195](http://llvm-reviews.chandlerc.com/rL200195),
[r200196](http://llvm-reviews.chandlerc.com/rL200196).

* The loop vectorizer gained a number of flags to help experiment with
changing thresholds. It now also only unrolls by powers of 2.
[r200212](http://llvm-reviews.chandlerc.com/rL200212),
[r200213](http://llvm-reviews.chandlerc.com/rL200213).

* The loop vectorizer now supports conditional stores by scalarizing (they are
put behind an if). This improves performance on the SPEC libquantum benchmark
by 4.15%.
[r200270](http://llvm-reviews.chandlerc.com/rL200270).

* MCSubtargetInfo is now explicitly passed to the `EmitInstruction`,
`EmitInstTo*`, `EncodeInstruction` and other functions in the MC module.
[r200345](http://llvm-reviews.chandlerc.com/rL200345) and others.

* llvm-readobj learned to decode ARM attributes.
[r200450](http://llvm-reviews.chandlerc.com/rL200450).

* Speculative execution of llvm.{sqrt,fma,fmuladd} is now allowed.
[r200501](http://llvm-reviews.chandlerc.com/rL200501).

## Clang commits

* Position Independent Code (PIC) is now turned on by default for Android
targets. [r200290](http://llvm-reviews.chandlerc.com/rL200290).

* The Parser::completeExpression function was introduced, which returns a list
of completions for a given expression and completion position.
[r200497](http://llvm-reviews.chandlerc.com/rL200497).

* The default CPU for 32-bit and 64-bit MIPS targets is now mips32r2 and
mips64r2 respectively. [r200222](http://llvm-reviews.chandlerc.com/rL200222).

* The ARM and AArch64 backends saw some refactoring to share NEON intrinsics.
[r200524](http://llvm-reviews.chandlerc.com/rL200524) and others.

## Other project commits

* Compiler-rt gained a cache invalidation implementation for AArch64
[r200317](http://llvm-reviews.chandlerc.com/rL200317).

* Compiler-rt now features an optimised implementation of `__clzdi2` and
`__clzsi2` for ARM. [r200394](http://llvm-reviews.chandlerc.com/rL200394).

* Compiler-rt's CMake files will now compile the library for ARM. Give it a go
and see what breaks. [r200546](http://llvm-reviews.chandlerc.com/rL200546).

* The iohandler LLDB branch was merged in. The commit log describes the
benefits. [r200263](http://llvm-reviews.chandlerc.com/rL200263).