[llvm-dev] LLVM Weekly - #331, May 4th 2020

[Alex Bradbury via llvm-dev]

LLVM Weekly - #331, May 4th 2020
================================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/331>.

Welcome to the three hundred and thirty-first 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

Emmanuel Roche has authored a
[fifth instalment](http://wiki.nervtech.org/doku.php?id=blog:2020:0425_jit_compiler_part5_improvements)
in the blog series on building a JIT C++ compiler with LLVM on Windows 10.


## On the mailing lists

* Tom Stellard [provided an updated RFC on migrating to GitHub
issues](http://lists.llvm.org/pipermail/llvm-dev/2020-April/141290.html). This
proposal would maintain issue numbers my overwriting existing ones with
migrated issue contents. A variant on this is currently being investigated,
which would involve creating a new repository (i.e. with no issues or PRs
already present), migrating the issues, and replacing the current llvm-project
repo on GitHub with it.

* Amara Emerson asked for input on [propagating int/float type information in
GlobalISel IR
translation](http://lists.llvm.org/pipermail/llvm-dev/2020-May/141350.html).

* JF Bastien follows up on the thread regarding `-ftrivial-auto-var-init=zero`
to [provide collated feedback from people's spoken
to](http://lists.llvm.org/pipermail/cfe-dev/2020-April/065361.html), while
Richard shares [more thoughts on
trapping](http://lists.llvm.org/pipermail/cfe-dev/2020-May/065372.html).

* The 6th edition of the MLIR (bi)weekly newsletter [is now
available](https://llvm.discourse.group/t/mlir-news-6th-edition-5-1-2020/949).

* ORC JIT Weekly #14 [is
out](http://lists.llvm.org/pipermail/llvm-dev/2020-May/141379.html). A
preliminary patch to support removable code in OrcV2 has been posted for
review.

* Matthew Malcomson started a [discussion on the exception unwinding ABI for
MTE](http://lists.llvm.org/pipermail/llvm-dev/2020-May/141345.html).

* Hal Finkel is intending to remove support for the IBM BG/Q supercomputer
from the PowerPC backend and is [asking if anyone still makes use of that
support](http://lists.llvm.org/pipermail/llvm-dev/2020-April/141295.html).

* Sam Parker kicked off an RFC thread on ["being explicit in the cost
model"](http://lists.llvm.org/pipermail/llvm-dev/2020-April/141263.html). His
latest patch aims to added a `TargetCostKind` as an argument to almost all
`get*Cost` methods.

* Sjoerd Meijer [proposes a new
llvm.set.loop.elements.i32](http://lists.llvm.org/pipermail/llvm-dev/2020-May/141341.html)
intrinsic to allow "tail predication" in the loop vectoriser.


## LLVM commits

* New IR constructs were added for 'preallocated', which provides a
replacement for inalloca. [3b0450a](https://reviews.llvm.org/rG3b0450acecb).

* SmallVector size and capacity will now use word-size integers when element
are small, in order to increase the maximum size of `SamllVector<char>`.
[dda3c19](https://reviews.llvm.org/rGdda3c19a361).

* The atomic expansion pass was updated to handle part-word LL/SC.
[25a4b19](https://reviews.llvm.org/rG25a4b1904c1).

* Lit now prints the number of tests that were discovered but not executed due
to test selection options. [8cb8fe9](https://reviews.llvm.org/rG8cb8fe909bc).

* WebAssembly SIMD opcodes have been renumbered to match the latest
specification (intended to the final reorganisation of the SIDM opcode space
before standardisation). [e0f5284](https://reviews.llvm.org/rGe0f52842c8b).


## Clang commits

* A draft specification for matrix support in Clang was committed.
[7363ffe](https://reviews.llvm.org/rG7363ffe95f0).

* The x86/x86-64 calling convention for `_ExtInt` was updated, so they are
passed indirectly if larger than the largest integer register and otherwise
passed like ints. `_ExtInt` must now be explicitly enabled per-target.
[5a1d9c0](https://reviews.llvm.org/rG5a1d9c0f5ac),
[911add1](https://reviews.llvm.org/rG911add149af).

* clang-format got better at parsing C# properties.
[44ad58b](https://reviews.llvm.org/rG44ad58b9915).


## Other project commits

* lld-macho development continues with support for basic symbol table output
and support for emitting trivial dylibs.
[4f0cccd](https://reviews.llvm.org/rG4f0cccdd7a0),
[62b8f32](https://reviews.llvm.org/rG62b8f32f769).

* MLIR gained a generic buffer assignment transformation, ported from
TensorFlow. [5c352e6](https://reviews.llvm.org/rG5c352e69e76).

* The scudo secure memory allocator now supports pattern-initialisation of
memory. [45b7d44](https://reviews.llvm.org/rG45b7d44ecb0).

* Flang now has a proposal document describing how uniquing of internal names
is done. [7875362](https://reviews.llvm.org/rG7875362986f).

* libcxx gained a small DSL for defining lit features and parameters.
[e82f0a5](https://reviews.llvm.org/rGe82f0a598f8).