[llvm-dev] LLVM Weekly - #344, August 3rd 2020

[Alex Bradbury via llvm-dev]

LLVM Weekly - #344, August 3rd 2020
===================================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/344>.

Welcome to the three hundred and forty-fourth 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.


## News and articles from around the web

LLVM 11.0.0-rc1 [has been
tagged](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143839.html).

The 2020 Linux Plumbers Conference [will feature an LLVM
microconference](https://www.linuxplumbersconf.org/blog/2020/llvm-microconference-accepted-into-2020-linux-plumbers-conference/).


## On the mailing lists

* Andrzej Warzynski [shares a new clang
tutorial](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143908.html).
[clang-tutor](https://github.com/banach-space/clang-tutor) provides a
collection of out-of-tree plugins for Clang with the intent to making it
easier for people to get started developing plugins.

* Andrzej Warzynski posted an RFC on [refactoring
libclangDriver/libclangFrontend to share with
Flang](http://lists.llvm.org/pipermail/cfe-dev/2020-July/066393.html).

* Stephen Neuendorffer sent a heads-up that [you may need to manually
'unwatch' the llvm/circt
repo](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143925.html) if
you're a member of the LLVM org.

* Johannes Doerfert proposed [adding support for heterogeneous LLVM-IR
modules](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143808.html).

* Petr Hosek shared [challenges he's facing related to the recent change in
ld.bfd tombstone
behaviour](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143920.html)
with suggestions for handling changes like this in the future.

* ORC JIT Weekly #18 [reports on the addition of the TargetProcessControl
API](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143804.html).

* "AE" asked about [filesystem support in libcxx on
Windows](http://lists.llvm.org/pipermail/libcxx-dev/2020-July/000899.html).
Stephan T. Lavavej [volunteered to contribute Microsoft's implementation to
libcxx](http://lists.llvm.org/pipermail/libcxx-dev/2020-July/000900.html).

* Zachary Turner enquired about the [status of the LLVM re-licensing
effort](http://lists.llvm.org/pipermail/llvm-foundation/2020-July/000213.html).
Hal Finkel
[reports](http://lists.llvm.org/pipermail/llvm-foundation/2020-July/000216.html)
that it is still in progress and the January 2019 target date will be revised
soon.

* Craig Topper raised the issue of [SimplifyCFG hoisting fences in if/else
branches](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143858.html), and
how this may harm attempts to use these fences to mitigate speculative
execution vulnerabilities.

* Son Tuan VU kicked off a [discussion on maintaining metadata other than
debug info through
compilation](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143639.html).
This triggered thoughts from others, [e.g. Lorenzo
Casalino](http://lists.llvm.org/pipermail/llvm-dev/2020-July/143869.html).


## LLVM commits

* llvm-jitlink gained a new `-harness` option to enhance testing.
[8ce8cee](https://reviews.llvm.org/rG8ce8cee1e1d).

* RISC-V Vector MC layer support was updated to bring it in line with the v0.9
draft specification. [47a4a27](https://reviews.llvm.org/rG47a4a27f472).

* The XRay infrastructure can now be used for runtime recursion detection.
[f2ab213](https://reviews.llvm.org/rGf2ab2134c7c).

* llvm-exegesis learned to use `LBR` for more precise measurements on Skylake
and onwards. [ee7caa7](https://reviews.llvm.org/rGee7caa75939).

* Support was removed from the PowerPC backend for the IBM BG/Q supercomputer.
[adffce7](https://reviews.llvm.org/rGadffce71538).

* The TableGen GlobalISelEmitter now allows output instructions with multiple
defs. [ee3feef](https://reviews.llvm.org/rGee3feef5aaa).

* File lock/unlock functions were added to LLVM's support library.
[5367369](https://reviews.llvm.org/rG536736995bf),
[032ed39](https://reviews.llvm.org/rG032ed39defc).

* The X86CondBrFolding pass was removed due to correctness issues.
[e1dd212](https://reviews.llvm.org/rGe1dd212c874).

* FileCheck `-dump-input` was extended with substitutions, and FileCheck will
now report captured variables in input dumps and traces.
[d680711](https://reviews.llvm.org/rGd680711b94e),
[9f86b8e](https://reviews.llvm.org/rG9f86b8ec41f).

* The CastContextHint enum was added to getCastInstrCost (e.g. Normal, Masked,
GatherScatter, etc). [60280e9](https://reviews.llvm.org/rG60280e9818a).


## Clang commits

* Clang's coverage support was fixed to not count lines containing only
comments.[b46176b](https://reviews.llvm.org/rGb46176bbb09).

* Support for the OpenMP 'present' motion modifier was added to Clang.
[9f2f3b9](https://reviews.llvm.org/rG9f2f3b9de63).


## Other project commits

* The dataflow sanitizer gained an efficient "fast16labels" instrumentation
mode, for use when the user needs no more than 16 labels.
[e2d0b44](https://reviews.llvm.org/rGe2d0b44a7cd).

* A WrapperGen tool was added to LLVM's libc implementation, to generate C
wrappers for the C++ LLVM libc implementation.s
[a32af82](https://reviews.llvm.org/rGa32af8252fd).

* The LLD ELF linker's CallGraphSort was ported to the COFF linker.
[763671f](https://reviews.llvm.org/rG763671f387f).

* Support for mutable types was added to MLIR.
[a518299](https://reviews.llvm.org/rGa51829913db).