[aarch64] Add an ASIMD variant of strlen for falkor

System Internals / glibc - Siddhesh Poyarekar [sourceware.org] - 15 August 2018 17:31 EDT

This variant of strlen uses vector loads and operations to reduce the size of the code and also eliminate the non-ascii fallback. This works very well for falkor because of its two vector units and efficient vector ops. In the best case it reduces latency of cases in bench-strlen by 48%, with gains throughout the benchmark. strlen-walk also sees uniform gains in the 5%-15% range.

Overall the routine appears to work better than the stock one for falkor regardless of the benchmark, length of string or cache state.

The same cannot be said of a53 and a72 though. a53 performance was greatly reduced and for a72 it was a bit of a mixed bag, slightly on the negative side but I reckon it might be fast in some situations.

- sysdeps/aarch64/strlen.S (__strlen): Rename to STRLEN. [!STRLEN](STRLEN): Set to __strlen.
- sysdeps/aarch64/multiarch/strlen.c: New file.
- sysdeps/aarch64/multiarch/strlen_generic.S: Likewise.
- sysdeps/aarch64/multiarch/strlen_asimd.S: Likewise.
- sysdeps/aarch64/multiarch/ifunc-impl-list.c (__libc_ifunc_impl_list): Add strlen.
- sysdeps/aarch64/multiarch/Makefile (sysdep_routines): Add strlen_generic and strlen_asimd.

436e4d5b96 [aarch64] Add an ASIMD variant of strlen for falkor
ChangeLog | 12 ++
sysdeps/aarch64/multiarch/Makefile | 3 +-
sysdeps/aarch64/multiarch/ifunc-impl-list.c | 4 +
sysdeps/aarch64/multiarch/strlen.c | 41 +++++++
sysdeps/aarch64/multiarch/strlen_asimd.S | 168 ++++++++++++++++++++++++++++
sysdeps/aarch64/multiarch/strlen_generic.S | 39 +++++++
sysdeps/aarch64/strlen.S | 10 +-
7 files changed, 273 insertions(+), 4 deletions(-)

Upstream: sourceware.org


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