[LLVMdev] LLVM Weekly - #21, May 26th 2014

[Alex Bradbury]

LLVM Weekly - #21, May 26th 2014
================================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/21>

Welcome to the 21st 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'm back in the UK and mostly recovered from the ensuing jetlag. I am however
disturbed that all mailing lists on [GMANE](http://gmane.org/) don't seem to
have been updated for the past week and have been unable to find any
explanation of what is going on online. GMANE is an important and massively
useful aggregrator and archiver of free software development lists and I
really hope these are only temporary problems. For this issue, I have instead
linked directly to the mailman archives at UIUC.

## News and articles from around the web

Jonathan Mah has written a [Clang plugin for checking key path strings in
Objective C
code](http://devetc.org/code/2014/05/17/safe-and-sane-key-paths.html). The
implementation is [available on
Github](https://github.com/jmah/Clang-KeyPathValidator).

LWN has published an [article about ThreadSanitizer
v2](http://lwn.net/Articles/598486/).

This week, the merge of the AArch64 and the Apple-contributed ARM64 backends
was completed. The old AArch64 was deleted and the result of merging code from
AArch64 in to ARM64 was renamed to AArch64.

A paper '[Static energy consumption analysis of LLVM IR
programs](http://arxiv.org/abs/1405.4565)' has been posted to arXiv.org.


## On the mailing lists

* Philip Reames wonders [why can't atomic loads and stores handle
floats](http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-May/073180.html).
David Chisnall has a good followup which explains [why just bitcasting floats
to use atomic load/store on them is far from
ideal](http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-May/073191.html).

* Louis Gerbarg has shared an [RFC on indexing of structs vs arrays in
getelementpointr](http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-May/073125.html).
This is inspired by his recent work to optimise getelementptr across different
basic blocks.

* Jingyue Wu [asks for advice on sinking incoming values of a PHI node in
CodeGenPrepare](http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-May/073079.html).
Louis Gerbarg points out that [these optimisations are similar to his recent
GetElementPtr
work](http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-May/073096.html).


## LLVM commits

* A new attribute, 'nonnull' has been added. When applied to a parameter or
return pointer this indicates it is not null, which may allow additional
optimisations (at least, avoiding comparisons between that value and null).
[r209185](http://reviews.llvm.org/rL209185),
[r209193](http://reviews.llvm.org/rL209193).

* The llvm.arm.undefined intrinsic has been added. This is used to generate
the 0xde opcode on ARM. It takes an integer parameter, which might be used by
the OS to implement custom behaviour on the trap.
[r209390](http://reviews.llvm.org/rL209390).

* The MIPS disassembler has seen some work. Some support has been added for
MIPS64r6 and various issues fixed.
[r209415](http://reviews.llvm.org/rL209415).

* LLVM learned the `-pass-remarks-missed` and `-pass-remarks-analysis` command
line options. `-pass-remarks-missed` shows diagnostics when a pass tried to
apply a transformation but couldn't. `-pass-remarks-analysis` shows
information about analysis results.
[r209442](http://reviews.llvm.org/rL209442).

* The documentation for the `llvm.mem.parallel_loop_access` metadata has been
updated. [r209507](http://reviews.llvm.org/rL209507).

* Old AArch64 has been removed and ARM64 renamed to AArch64.
[r209576](http://reviews.llvm.org/rL209576),
[r209577](http://reviews.llvm.org/rL209577).


## Clang commits

* clang-format has seen more JS support. It can now reformat ES6 arrow
functions and ES6 destructuring assignments.
[r209112](http://reviews.llvm.org/rL209112),
[r209113](http://reviews.llvm.org/rL209113).

* Experimental checkers for the clang static analyzer are [now
documented](http://clang.llvm.org/analyzer/alpha_checks.html).
[r209131](http://reviews.llvm.org/rL209131).

* Support was added to clang for global named registers, using the LLVM
intrinsics which were recently added.
[r209149](http://reviews.llvm.org/rL209149).

* Clang learned the `no_split_stack` attribute to turn off split stacks on a
per-function bases. [r209167](http://reviews.llvm.org/rL209167).

* Clang learned the `flatten` attribute. This causes calls within the function
to be inlined where possible. [r209217](http://reviews.llvm.org/rL209217).

* An initial version of codegen for pragma omp simd has been committed. This
also adds CGLoopInfo which is a helper for marking memory instructions with
`llvm.mem.parallel_loop_access` metadata.
[r209411](http://reviews.llvm.org/rL209411).

* The pragma `clang optimize {on,off}` has been implemented. This allows you
to selectively disable optimisations on certain functions.
[r209510](http://reviews.llvm.org/rL209510).

* An implementation of Microsoft ABI-compatible RTTI (run-time type
information) has landed. [r209523](http://reviews.llvm.org/rL209523).


## Other project commits

* 'Chained origins' as used by MemorySanitizer has been redesigned.
[r209284](http://reviews.llvm.org/rL209284).