[LLVMdev] LLVM Weekly - #28, Jul 14th 2014

[Alex Bradbury]

LLVM Weekly - #28, Jul 14th 2014
===============================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/28>.

Welcome to the twenty-eightth 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'll be at the [GNU Tools Cauldron
2014](https://gcc.gnu.org/wiki/cauldron2014) next weekend, being held at the
University of Cambridge Computer Laboratory (which handily is also where I
work). If you're there, do say hi.


## News and articles from around the web

An update on Clang/LLVM on Windows has been [posted on the LLVM
blog](http://blog.llvm.org/2014/07/clangllvm-on-windows-update.html).
Impressive progress has been made, and as I mentioned last week the [MSVC
compatibility page](http://clang.llvm.org/docs/MSVCCompatibility.html) has
been updated.

There is (somewhat amazingly) now a [Pascal-86 frontend for
LLVM](http://john-tornblom.github.io/llvm-p86/). The compiler frontend is
written entirely in Python. More information is available in the author's
[Master's thesis](http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-105456)
(via [Phoronix](http://www.phoronix.com/scan.php?page=news_item&px=MTczODY)).


## On the mailing lists

* Edward Diener has [kicked off a discussion on whether clang-cl should
reproduce buggy VC++ preprocessor
behaviour](http://article.gmane.org/gmane.comp.compilers.clang.devel/37699). A
concern is that this might hold back people wanting to use preprocessor
metaprogramming on the Windows platform. As is pointed out in one of the
responses, bug-for-bug compatibility mode could always be disabled via a new
flag.

* Corey Richardson has a [query about using clang-c for a bindings
generator](http://article.gmane.org/gmane.comp.compilers.clang.devel/37761).
No responses yet, but it's certainly of interest to me.

* Kuba Břečka [proposes extending LLDB to offer tighter integration with
Address Sanitizer-enabled
binaries](http://article.gmane.org/gmane.comp.compilers.llvm.devel/74718).

* Peter Collingbourne has [proposed offering a native object on-disk module
format storing LLVM bitcode in an ELF/COFF/MACH-O
section](http://article.gmane.org/gmane.comp.compilers.llvm.devel/74602). Dan
Liew [points out that unrecognised sections are included in the output by the
linker](http://article.gmane.org/gmane.comp.compilers.llvm.devel/74641),
meaning if you linked these .o files the bitcode would be included in the
produced binary. Peter says the current plan wouldn't have these object files
used directly by the linker.


## LLVM commits

* FastISel gained some infrastructure to support a target-independent call
lowering hook as well as target-independent lowering for the patchpoint
intrinsic. [r212848](http://reviews.llvm.org/rL212848),
[r212849](http://reviews.llvm.org/rL212849).

* DominanceFrontier has been templatified, so in theory it can now be used for
MachineBasicBlocks (where previously it was only usable with BasicBlocks).
[r212885](http://reviews.llvm.org/rL212885).

* The quality of results for CallSite vs CallSite BasicAA queries has been
improved by making use of knowledge about certain intrinsics such as memcpy
and memset. [r212572](http://reviews.llvm.org/rL212572).

* Work on overhauling x86 vector lowering continues. Chandler now reports that
with the new codepath enabled, LLVM is now at performance pairty with GCC for
the core C loops of the x264 code when compiling for SSE2/SSE3.
[r212610](http://reviews.llvm.org/rL212610).

* ASM instrumentation for AddressSanitizer is now generated entirely in
MachineCode, without relying on runtime helper functions.
[r212455](http://reviews.llvm.org/rL212455).

* Generation of the new mips.abiflags section was added to the MIPS backend.
[r212519](http://reviews.llvm.org/rL212519).

* isDereferenceablePointer will now look through some bitcasts.
[r212686](http://reviews.llvm.org/rL212686).


## Clang commits

* A new checker was added, to flag code that tests a variable for 0 after
using it as a denominator (implying a potential division by zero).
[r212731](http://reviews.llvm.org/rL212731).

* Clang gained initial support for omp parallel for, the omp parallel sections
directive, and omp task. [r212453](http://reviews.llvm.org/rL212453),
[r212516](http://reviews.llvm.org/rL212516),
[r212804](http://reviews.llvm.org/rL212804).

* On the ARM target, LLVM's atomicrmw instructions will be used when
ldrex/strex are available. [r212598](http://reviews.llvm.org/rL212598).

* Support was adding for mips-img-linux-gnu toolchains.
[r212719](http://reviews.llvm.org/rL212719).


## Other project commits

* ThreadSanitizer's deadlock detector is enabled by default after being
battle-tested on the Chromium codebase for some time.
[r212533](http://reviews.llvm.org/rL212533).

* Support for Android's bionic C library has been added to libcxx.
[r212724](http://reviews.llvm.org/rL212724).

* LLDB's Python scripting interface should now work on Windows.
[r212785](http://reviews.llvm.org/rL212785).