[llvm-dev] Orc JIT Weekly #33 -- Orc Runtime patches, JITLink and C API improvements

Lang Hames via llvm-dev llvm-dev at lists.llvm.org
Sun May 9 23:09:34 PDT 2021

Hi All,

Highlights this week (and for all the weeks I've missed over the last
couple of months):

(1) The Orc runtime patches have started to land in the mainline [1], [2].
It's slow going while the initial infrastructure is tidied up and reviewed
(CMake is not my strong suit), but I expect the pace to pick up after that.
My aim is to have everything in the runtime preview branch tidied up and
landed in the mainline by the end of June.

(2) ExecutionSession::dispatchMaterialization has been generalized to
dispatchTask. This will allow query callbacks to be dispatched (rather than
being run immediately on the current thread), which will prevent work from
piling up on one thread when one object file emission causes several query
callbacks to fire. [3]

(3) JITLink has acquired generic x86-64 edge kinds and utilities, and the
MachO x86-64 backend has been rewritten to take advantage of them rather
than using edge types specific to MachO [4]. This will eventually improve
code sharing between the MachO and ELF backends, though the ELF backend has
not been rewritten to use the new edge kinds yet.

I expect this pattern (format agnostic edge kinds and utilities) to be
followed by other architectures in the future. Generic arm64 edges and
utilities are the next goal.

Side note: This work actually landed all the way back on March 11th, but I
failed to include a note on it in Orc JIT Weekly #32, which was the only
other edition since then. Oops!

(4) Stefan Granitz landed ELF debugging support for JITLink in [5] (also
back in March). This is big news as it closes one of the significant
remaining functionality gaps between JITLink and RuntimeDyld. Thanks

(5) The C API has acquired some unit tests in [6] courtesy of Mats Larsen.
Thanks Mats!

The C API test shook loose some bugs in the existing APIs, and led to
contract changes on some of the functions. If you're using the new Orc C
bindings (especially the LLVMOrcAbsoluteSymbols function) please take a
moment to review the changes to see if they affect you.

-- Lang.

[2] https://reviews.llvm.org/D102080
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