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llvm / llvm-project / lld / 5cbd0695f56f7a778dd860913a2339f152a725ae
commit5cbd0695f56f7a778dd860913a2339f152a725ae[log] [tgz]
authorJez Ng <jezng@fb.com>Thu Feb 25 13:27:40 2021 -0500
committerCopybara-Service <copybara-worker@google.com>Fri Feb 26 22:04:06 2021 -0800
treedf5b7a1c49faeca16ededd096be273a800bdc472
parentda78b1cacf788edcf2b32a33fd87ac91ff8693e3 [diff]
[lld-macho] Basic support for linkage and visibility attributes in LTO

When parsing bitcode, convert LTO Symbols to LLD Symbols in order to perform
resolution. The "winning" symbol will then be marked as Prevailing at LTO
compilation time. This is similar to what the other LLD ports do.

This change allows us to handle `linkonce` symbols correctly, and to deal with
duplicate bitcode symbols gracefully. Previously, both scenarios would result in
an assertion failure inside the LTO code, complaining that multiple Prevailing
definitions are not allowed.

While at it, I also added basic logic around visibility. We don't do anything
useful with it yet, but we do check that its value is valid. LLD-ELF appears to
use it only to set FinalDefinitionInLinkageUnit for LTO, which I think is just a
performance optimization.

From my local experimentation, the linker itself doesn't seem to do anything
differently when encountering linkonce / linkonce_odr / weak / weak_odr. So I've
only written a test for one of them. LLD-ELF has more, but they seem to mostly
be testing the intermediate bitcode output of their LTO backend...? I'm far from
an expert here though, so I might very well be missing things.

Reviewed By: #lld-macho, MaskRay, smeenai

Differential Revision: https://reviews.llvm.org/D94342

GitOrigin-RevId: 84579fc24f03c8ca778e70325dad2166f1deaee3
5 files changed
tree: df5b7a1c49faeca16ededd096be273a800bdc472
  1. cmake/
  2. COFF/
  3. Common/
  4. docs/
  5. ELF/
  6. include/
  7. lib/
  8. MachO/
  9. MinGW/
  10. test/
  11. tools/
  12. unittests/
  13. utils/
  14. wasm/
  15. .clang-format
  16. .clang-tidy
  17. .gitignore
  18. CMakeLists.txt
  19. CODE_OWNERS.TXT
  20. LICENSE.TXT
  21. README.md
README.md

LLVM Linker (lld)

This directory and its subdirectories contain source code for the LLVM Linker, a modular cross platform linker which is built as part of the LLVM compiler infrastructure project.

lld is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt.

Benchmarking

In order to make sure various developers can evaluate patches over the same tests, we create a collection of self contained programs.

It is hosted at https://s3-us-west-2.amazonaws.com/linker-tests/lld-speed-test.tar.xz

The current sha256 is 10eec685463d5a8bbf08d77f4ca96282161d396c65bd97dc99dbde644a31610f.