[llvm-dev] LLVM Weekly - #348, August 31st 2020

[Alex Bradbury via llvm-dev]

LLVM Weekly - #348, August 31st 2020
====================================

If you prefer, you can read a HTML version of this email at
<http://llvmweekly.org/issue/348>.

Welcome to the three hundred and forty-eighth 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

The program for the 2020 Virtual LLVM Developers' Meeting [has been
announced](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144566.html)
and [registration is now
open](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144649.html).

The deadline to submit to this year's LLVM in HPC workshp [has been
extended](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144602.html) to
September 4th.


## On the mailing lists

* Josh Stone provided a [report on the Rust performance impact of LLVM
11.0.0-rc2](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144594.html).

* Stephen Tozer [provided a heads-up about work to change `llvm.dbg.value` and
`DBG_VALUE` to support multiple location
operands](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144589.html).

* Alexey Lapshin [proposes
llvm-dwarfutil](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144579.html),
a dsymutil-like tool for ELF.

* James Y Knight [proposes to remove MMX
support](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144670.html)
(other than the MC layer assembler definitions). The proposal is to implement
the intrinsics in `*mmintrin.h` that currently use MMX in terms of SSE/SSE2
compiler builtins.

* Xing Guo provided a [report on their GSoC project to add DWARF support to
yaml2obj](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144666.html).

* Fangrui Song [suggests making --warn-backrefs the default for
LLD](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144634.html).

* Stefan Stipanovic is [intending to make intrinsics have attributes such as
nofree, nosync, and willreturn by
default](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144631.html) and
asks for anyone to share any concerns in the next ~2 weeks.


## LLVM commits

* The machine function splitter was committed. For a clang bootstrap it
produces a 2.33% runtime improvement with a ~32% reduction in I-TLB and D-TLB
misses. [94faada](https://reviews.llvm.org/rG94faadaca4e).

* Support was added for heap profiling instrumentation.
[7ed8124](https://reviews.llvm.org/rG7ed8124d46f).

* llvm-lipo gained support for bitcode files.
[c6f7ac0](https://reviews.llvm.org/rGc6f7ac0071a).

* llvm-dwarfdump was sped up by almost 4x when redirecting output to a file.
[b20a4e2](https://reviews.llvm.org/rGb20a4e293c3).

* The loop vectorizer gained two fallback strategies for if tail-folding
fails: don't vectorise at all or vectorise using a scalar epilogue.
[bda8fbe](https://reviews.llvm.org/rGbda8fbe2d2a).

* The constant propagation pass was removed as it had now users outside of
unit tests. [486ed88](https://reviews.llvm.org/rG486ed885339).

* MC layer support was added for the RISC-V Vector Zvamo extension.
[888c02d](https://reviews.llvm.org/rG888c02deee2).

* AArch64 will now generate and parse SEH assembly directives, ensuring you
get the same output whether generating code directly to an object file or if
generating assembly and then assembling that.
[5b86d13](https://reviews.llvm.org/rG5b86d130e2b).


## Clang commits

* Support for X86 -march=sapphirerapids was committed.
[e02d081](https://reviews.llvm.org/rGe02d081f2b6).

* The `arm_sve_vector_bits` attribute is now supported.
[feed5a7](https://reviews.llvm.org/rGfeed5a7239d),
[4258734](https://reviews.llvm.org/rG42587345a3a).


## Other project commits

* An unsigned shift base sanitizer was added to detect when an unsigned left
shift overflows. Although this isn't undefined behaviour, it can be a source
of bugs. [82d29b3](https://reviews.llvm.org/rG82d29b397bb).

* LLVM's libc gained implementations for sqrt, sqrtf, and sqrtl.
[5078825a](https://reviews.llvm.org/rG5078825aa98).

* A new Pattern Descriptor Language (PDL) Interpreter dialect was added to
MLIR. [d289a97](https://reviews.llvm.org/rGd289a97f914).