Reland #120514 after 2f6e3df08a8b7cd29273980e47310cf09c6fdbd8 fixed
iteration order issue and libstdc++/libc++ differences.
---
Both options instruct the linker to optimize section layout with the
following goals:
* `--bp-compression-sort=[data|function|both]`: Improve Lempel-Ziv
compression by grouping similar sections together, resulting in a
smaller compressed app size.
* `--bp-startup-sort=function --irpgo-profile=<file>`: Utilize a
temporal profile file to reduce page faults during program startup.
The linker determines the section order by considering three groups:
* Function sections ordered according to the temporal profile
(`--irpgo-profile=`), prioritizing early-accessed and frequently
accessed functions.
* Function sections. Sections containing similar functions are placed
together, maximizing compression opportunities.
* Data sections. Similar data sections are placed together.
Within each group, the sections are ordered using the Balanced
Partitioning algorithm.
The linker constructs a bipartite graph with two sets of vertices:
sections and utility vertices.
* For profile-guided function sections:
+ The number of utility vertices is determined by the symbol order
within the profile file.
+ If `--bp-compression-sort-startup-functions` is specified, extra
utility vertices are allocated to prioritize nearby function similarity.
* For sections ordered for compression: Utility vertices are determined
by analyzing k-mers of the section content and relocations.
The call graph profile is disabled during this optimization.
When `--symbol-ordering-file=` is specified, sections described in that
file are placed earlier.
Co-authored-by: Pengying Xu <xpy66swsry@gmail.com>
The ELF/bp-section-orderer.s test is failing on some buildbots due to
what seems like non-determinism issues, see comments on the original PR
and #125450
Reverting to green the build.
This reverts commit 0154dce8d39d2688b09f4e073fe601099a399365 and
follow-up commits 046dd4b28b9c1a75a96cf63465021ffa9fe1a979 and
c92f20416e6dbbde9790067b80e75ef1ef5d0fa4.
Add new ELF linker options for profile-guided section ordering
optimizations:
- `--irpgo-profile=<file>`: Read IRPGO profile data for use with startup
and compression optimizations
- `--bp-startup-sort={none,function}`: Order sections based on profile
data to improve star tup time
- `--bp-compression-sort={none,function,data,both}`: Order sections
using balanced partitioning to improve compressed size
- `--bp-compression-sort-startup-functions`: Additionally optimize
startup functions for compression
- `--verbose-bp-section-orderer`: Print statistics about balanced
partitioning section ordering
Thanks to the @ellishg, @thevinster, and their team's work.
---------
Co-authored-by: Fangrui Song <i@maskray.me>
