42cc454777
Two optimizations to make getSectionPiece O(1) for common cases:
1. For non-string fixed-size merge sections, use direct computation
(offset / entsize) instead of binary search.
2. Pre-resolve piece indices for non-section Defined symbols during
splitSections. The piece index and intra-piece offset are packed
into Defined::value as ((pieceIdx+1) << 32) | intraPieceOffset,
replacing repeated binary searches (MarkLive, includeInSymtab,
getRelocTargetVA) with a single upfront resolution.
On x86-64, references to mergeable strings use local labels:
leaq .LC0(%rip), %rax # R_X86_64_PC32 .LC0-4
The relocations use non-section symbols and benefit from optimization 2.
On many other targets (e.g. AArch64), the addend is 0 and the assembler
adjusts such relocations to reference section symbols, which still use
binary search.
On a clang link (clang-relassert reproduce tarball, x86-64):
- --gc-sections: 1.05x as fast
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.