[PATCH] D13950: ELF2: Implement --gc-sections.

[Rafael Espíndola via llvm-commits]

Just applied the patch locally to review it. There are a few
formatting issues. Please git-clang-format.

On 21 October 2015 at 13:30, Rui Ueyama <ruiu at google.com> wrote:
> ruiu created this revision.
> ruiu added a reviewer: rafael.
> ruiu added a subscriber: llvm-commits.
>
> Section garbage collection is a feature to remove unused sections
> from outputs. Unused sections are sections that cannot be reachable
> from known GC-root symbols or sections. Naturally the feature is
> implemented as a mark-sweep garbage collector.
>
> In this patch, I added Live bit to InputSectionBase. If and only
> if Live bit is on, the section will be written to the output.
> Starting from GC-root symbols or sections, a new function, markLive(),
> visits all reachable sections and sets their Live bits. Writer then
> ignores sections whose Live bit is off, so that such sections are
> excluded from the output.
>
> This change has small negative impact on performance. The time to
> link Clang changes from 0.356s to 0.386s, or +8%.
>
> It reduces Clang size from 57,764,984 bytes to 55,296,600 bytes.
> That is 4.3% reduction.
>
>
> http://reviews.llvm.org/D13950
>
> Files:
>   ELF/CMakeLists.txt
>   ELF/Config.h
>   ELF/Driver.cpp
>   ELF/InputFiles.cpp
>   ELF/InputFiles.h
>   ELF/InputSection.h
>   ELF/MarkLive.cpp
>   ELF/Options.td
>   ELF/OutputSections.cpp
>   ELF/SymbolTable.h
>   ELF/Symbols.h
>   ELF/Writer.cpp
>   ELF/Writer.h
>   test/elf2/gc-sections.s
>