[PATCH] D152840: A new code layout algorithm for function reordering [3a/3]

[Sergey Pupyrev via Phabricator via llvm-commits]

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upd


We are brining a new algorithm for function layout (reordering) based on the
call graph (extracted from a profile data). The algorithm is an improvement of
top of a known heuristic, C^3. It tries to co-locate hot and frequently executed
together functions in the resulting ordering. Unlike C^3, it explores a larger
search space and have an objective closely tied to the performance of
instruction and i-TLB caches. Hence, the name CDS = Cache-Directed Sort.
The algorithm can be used at the linking or post-linking (e.g., BOLT) stage.

This diff adds a linker option to replace the existing C^3 heuristic with CDS.

**Perf-impact**
clang-10 binary (built with LTO+AutoFDO/CSSPGO): wins on top of C^3 in [0.3%..0.8%]
rocksDB-8 binary (built with LTO+CSSPGO): wins on top of C^3 in [0.8%..1.5%]


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D152840

Files:
  lld/ELF/CMakeLists.txt
  lld/ELF/CallGraphSort.cpp
  lld/ELF/CallGraphSort.h
  lld/ELF/Config.h
  lld/ELF/Driver.cpp
  lld/ELF/Options.td

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