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dd647e3e60
Apologies for the large change, I looked for ways to break this up and all of the ones I saw added real complexity. This change focuses on the option's prefixed names and the array of prefixes. These are present in every option and the dominant source of dynamic relocations for PIE or PIC users of LLVM and Clang tooling. In some cases, 100s or 1000s of them for the Clang driver which has a huge number of options. This PR addresses this by building a string table and a prefixes table that can be referenced with indices rather than pointers that require dynamic relocations. This removes almost 7k dynmaic relocations from the `clang` binary, roughly 8% of the remaining dynmaic relocations outside of vtables. For busy-boxing use cases where many different option tables are linked into the same binary, the savings add up a bit more. The string table is a straightforward mechanism, but the prefixes required some subtlety. They are encoded in a Pascal-string fashion with a size followed by a sequence of offsets. This works relatively well for the small realistic prefixes arrays in use. Lots of code has to change in order to land this though: both all the option library code has to be updated to use the string table and prefixes table, and all the users of the options library have to be updated to correctly instantiate the objects. Some follow-up patches in the works to provide an abstraction for this style of code, and to start using the same technique for some of the other strings here now that the infrastructure is in place.
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.