[llvm-dev] LLVM Weekly - #306, November 11th 2019

[Alex Bradbury via llvm-dev]

LLVM Weekly - #306, November 11th 2019
======================================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/306>.

Welcome to the three hundred and sixth 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](https://www.linkedin.com/in/alex-bradbury/). 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.

As many of you know, I co-founded a not-for-profit collaborative engineering
company, lowRISC. We've had a [huge
announcement](https://www.lowrisc.org/blog/2019/11/announcing-opentitan-the-first-transparent-silicon-root-of-trust/)
last week, publicly announcing the world's first open source silicon root of
trust - OpenTitan.


## News and articles from around the web

The call for papers for the 4th LLVM performance workshop at CGO [has been
posted](http://lists.llvm.org/pipermail/llvm-dev/2019-November/136649.html).
The deadline for submissions in teh 5th Jan, and the workshop will take place
on Feb 23rd in San Diego.

Herb Sutter has posted a [trip report from the Autumn ISO C++ standard
meeting](https://herbsutter.com/2019/11/09/trip-report-autumn-iso-c-standards-meeting-belfast/).


## On the mailing lists

* Mehdi Amini started a thread on [allowing LLVM contributions through GitHub
pull
requests](http://lists.llvm.org/pipermail/llvm-dev/2019-November/136579.html).
This generated a huge amount of discussion, pro and con.

* Levi Aul is seeking feedback on supporting an [unlimited width integer
type](http://lists.llvm.org/pipermail/cfe-dev/2019-November/063838.html).
David Chisnall [provided some
thoughts](http://lists.llvm.org/pipermail/cfe-dev/2019-November/063852.html).

* Ehud Katz posted an RFC on [exposing the waymarking
algorithm](http://lists.llvm.org/pipermail/llvm-dev/2019-November/136491.html)
from the 'Use' class as an independent utility.

* Bardia Mahjour sent out the [loop optimisation working group meeting
minutes](http://lists.llvm.org/pipermail/llvm-dev/2019-November/136603.html)
for last week.


## LLVM commits

* The 'freeze' instruction was added to LLM IR, which can be used to stop
propagation of undef and poison values.
[58acbce](https://reviews.llvm.org/rG58acbce3def),
[2d21068](https://reviews.llvm.org/rG2d21068d9fa).

* GlobalISel saw a number of documentation improvements including docs on
KnownBits analysis, debugging with the block extractor, and GMIR and
GenericOpCode references.
[312932a](https://reviews.llvm.org/rG312932a3346),
[7060840](https://reviews.llvm.org/rG7060840bc9c),
[ad0dfb0](https://reviews.llvm.org/rGad0dfb0a253).

* SystemZ gained support for the GHC calling convention.
[22f9429](https://reviews.llvm.org/rG22f9429149a).

* DFAPacketizer was updated to allow up to 64 functional units.
[39525a6](https://reviews.llvm.org/rG39525a67238).

* DWARFDebugLocLists started to moved to an incremental parsing model.
[e1f8c8a](https://reviews.llvm.org/rGe1f8c8a16f4).

* InstCombine will now canonicalise shift+logic+shift to reduce the dependency
chain. [d9ccb63](https://reviews.llvm.org/rGd9ccb6367a1).

* The `-consider-local-interval-cost` options for the greedy register
allocator is now enabled by default for AArch64. This has very minor impact
which the commit message documents.
[f649f24](https://reviews.llvm.org/rGf649f24d388).

* Development of the data dependency graph continues with the addition of Pi
Blocks. [f0af11d8](https://reviews.llvm.org/rGf0af11d86f8).


## Clang commits

* Syntax nodes were added for most comment statements.
[58fa50f](https://reviews.llvm.org/rG58fa50f4370).

* Clang's sysroot computation will now do a better job for the RISC-V target
in the case that no GCC install is detected.
[de61aa3](https://reviews.llvm.org/rGde61aa3118b).


## Other project commits

* The old Python-based build system was dropped from libclc.
[d6e0e6d](https://reviews.llvm.org/rGd6e0e6d255a).

* std::midpoint was optimised for integers.
[586952f](https://reviews.llvm.org/rG586952f4cef).