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The Global Function Merger (https://discourse.llvm.org/t/rfc-global-function-merging/82608) pass optimistically creates merged instances of functions and suffixes their names with `.Tgm`. Then in the linker, ICF will (hopefully) fold these `.Tgm` functions. For example, a function `foo` might become a thunk `foo` that calls a merged function `foo.Tgm`. Since IRPGO runs before the global merger, we will only have a profile for `foo`. We want to correlate this profile to both `foo` and `foo.Tgm` so they can both be ordered to improve startup time. I built a large binary and found that it increased the number of functions ordered for startup, as expected. ``` Functions for startup: 12049 -> 12697 Functions for compression: 34733 -> 34707 ``` The reason why we don't see a larger improvement is because there are some cases where the code was accidentally working: `getRootSymbol("foo.llvm.5555.Tgm")` already returns `foo`.
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.