[all-commits] [llvm/llvm-project] 0c3704: [ELF] Deduplicate names of local symbols only with...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0c3704fdbd901e5f51acf11a85278bf9214ae7b2
      https://github.com/llvm/llvm-project/commit/0c3704fdbd901e5f51acf11a85278bf9214ae7b2
  Author: Fangrui Song <i at maskray.me>
  Date:   2022-02-01 (Tue, 01 Feb 2022)

  Changed paths:
    M lld/ELF/SyntheticSections.cpp
    M lld/docs/ReleaseNotes.rst
    A lld/test/ELF/strtab-dedup.s

  Log Message:
  -----------
  [ELF] Deduplicate names of local symbols only with -O2

The deduplication requires a DenseMap of the same size of the local part of
.strtab . I optimized it in e20544543478b259eb09fa0a253d4fb1a5525d9e but it is
still quite slow.

For Release build of clang, deduplication makes .strtab 1.1% smaller and makes the link 3% slower.
For chrome, deduplication makes .strtab 0.1% smaller and makes the link 6% slower.

I suggest that we only perform the optimization with -O2 (default is -O1).
Not deduplicating local symbol names will simplify parallel symbol table write.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D118577