[PATCH v2 00/15] RISC-V: Add Zbb-optimized string routines as ifuncs

[Christoph Müllner]

Ping.

On Mon, May 27, 2024 at 1:19 PM Christoph Müllner
<christoph.muellner@vrull.eu> wrote:
>
> Glibc recently got hwprobe() support for RISC-V, which allows querying
> avaiable extensions at runtime.  On top of that an optimized memcpy()
> routine (for fast unaligned accesses) has been merged, which is built by
> recompiling the generic C code with a different compiler flag.  An ifunc
> resolver then detects which routine should be run using hwprobe().
>
> This patchset follows this idea and recompiles the following functions
> for Zbb (via function attributes) and enables the existing Zbb/orc.b
> optimization in riscv/string-fza.h:
> memchr, memrchr, strchrnul, strcmp, strlen, strncmp.
> The resulting optimized routines are then selected by the resolver function
> if the Zbb extension is present at runtime.
>
> To use target function attributes, a few issues had to be resovled:
> - The functions above got a mechanism to be compiled with function attributes
>   (patches 2-7).  Only those routines have been touched, which are
>   required for the purpose of this patchset.
> - Ensuring that inlined functions also get the same function attributes
>   (first patch).
> - Add mechanism to explicitly enable the orc.b optimization for string functions
>   (patch 8), which is a bit inspired by USE_FFS_BUILTIN.
>
> One of the design questions is, if Zbb represents a broad enough optimization
> target.  Tests with Zb* extensions showed, that no further code improvements
> can be achieved with them.  Also most other extensions likely won't affect
> the generated code for string routines (ignoring vector instructions, which
> are a different topic).  Therefore, Zbb seemed like a sufficient target.
>
> This series was tested by writing a simple test program to invoke the
> libc routines (e.g. strcmp) and a modified QEMU that reports the
> emulation of orc.b on stderr.  With that the QEMU can be used to test
> if the optimized routines are executed (-cpu "rv64,zbb=[false,true]").
> Further, this series was tested with SPEC CPU 2017 intrate with Zbb
> enabled.  The function attribute detection mechanism was tested with
> GCC 13 and GCC 14.
>
> Changes in v2:
> - Drop "Use .insn directive form for orc.b"
> - Introduce use of target function attribute (and all depenendcies)
> - Introduce detection of target function attribute support
> - Make orc.b optimization explicit
> - Small cleanups
>
> Christoph Müllner (15):
>   cdefs: Add mechanism to add attributes to __always_inline functions
>   string/memchr: Add mechanism to set function attributes
>   string/memrchr: Add mechanism to set function attributes
>   string/strchrnul: Add mechanism to set function attributes
>   string/strcmp: Add mechanism to set function attributes
>   string/strlen: Add mechanism to set function attributes
>   string/strncmp: Add mechanism to set function attributes
>   RISC-V: string-fz[a,i].h: Make orc.b optimization explicit
>   RISC-V: Add compiler test for Zbb function attribute support
>   RISC-V: Add Zbb optimized memchr as ifunc
>   RISC-V: Add Zbb optimized memrchr as ifunc
>   RISC-V: Add Zbb optimized strchrnul as ifunc
>   RISC-V: Add Zbb optimized strcmp as ifunc
>   RISC-V: Add Zbb optimized strlen as ifunc
>   RISC-V: Add Zbb optimized strncmp as ifunc
>
>  config.h.in                                   |  3 +
>  misc/sys/cdefs.h                              |  8 ++-
>  string/memchr.c                               |  5 ++
>  string/memrchr.c                              |  5 ++
>  string/strchrnul.c                            |  5 ++
>  string/strcmp.c                               |  8 +++
>  string/strlen.c                               |  5 ++
>  string/strncmp.c                              |  8 +++
>  sysdeps/riscv/configure                       | 27 ++++++++
>  sysdeps/riscv/configure.ac                    | 18 +++++
>  sysdeps/riscv/multiarch/memchr-generic.c      | 24 +++++++
>  sysdeps/riscv/multiarch/memchr-zbb.c          | 23 +++++++
>  sysdeps/riscv/multiarch/memrchr-generic.c     | 24 +++++++
>  sysdeps/riscv/multiarch/memrchr-zbb.c         | 23 +++++++
>  sysdeps/riscv/multiarch/strchrnul-generic.c   | 24 +++++++
>  sysdeps/riscv/multiarch/strchrnul-zbb.c       | 23 +++++++
>  sysdeps/riscv/multiarch/strcmp-generic.c      | 24 +++++++
>  sysdeps/riscv/multiarch/strcmp-zbb.c          | 23 +++++++
>  sysdeps/riscv/multiarch/strlen-generic.c      | 24 +++++++
>  sysdeps/riscv/multiarch/strlen-zbb.c          | 23 +++++++
>  sysdeps/riscv/multiarch/strncmp-generic.c     | 26 +++++++
>  sysdeps/riscv/multiarch/strncmp-zbb.c         | 25 +++++++
>  sysdeps/riscv/string-fza.h                    | 22 +++++-
>  sysdeps/riscv/string-fzi.h                    | 20 +++++-
>  .../unix/sysv/linux/riscv/multiarch/Makefile  | 23 +++++++
>  .../linux/riscv/multiarch/ifunc-impl-list.c   | 67 +++++++++++++++++--
>  .../unix/sysv/linux/riscv/multiarch/memchr.c  | 60 +++++++++++++++++
>  .../unix/sysv/linux/riscv/multiarch/memrchr.c | 63 +++++++++++++++++
>  .../sysv/linux/riscv/multiarch/strchrnul.c    | 63 +++++++++++++++++
>  .../unix/sysv/linux/riscv/multiarch/strcmp.c  | 59 ++++++++++++++++
>  .../unix/sysv/linux/riscv/multiarch/strlen.c  | 59 ++++++++++++++++
>  .../unix/sysv/linux/riscv/multiarch/strncmp.c | 59 ++++++++++++++++
>  32 files changed, 863 insertions(+), 10 deletions(-)
>  create mode 100644 sysdeps/riscv/multiarch/memchr-generic.c
>  create mode 100644 sysdeps/riscv/multiarch/memchr-zbb.c
>  create mode 100644 sysdeps/riscv/multiarch/memrchr-generic.c
>  create mode 100644 sysdeps/riscv/multiarch/memrchr-zbb.c
>  create mode 100644 sysdeps/riscv/multiarch/strchrnul-generic.c
>  create mode 100644 sysdeps/riscv/multiarch/strchrnul-zbb.c
>  create mode 100644 sysdeps/riscv/multiarch/strcmp-generic.c
>  create mode 100644 sysdeps/riscv/multiarch/strcmp-zbb.c
>  create mode 100644 sysdeps/riscv/multiarch/strlen-generic.c
>  create mode 100644 sysdeps/riscv/multiarch/strlen-zbb.c
>  create mode 100644 sysdeps/riscv/multiarch/strncmp-generic.c
>  create mode 100644 sysdeps/riscv/multiarch/strncmp-zbb.c
>  create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/memchr.c
>  create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/memrchr.c
>  create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/strchrnul.c
>  create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/strcmp.c
>  create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/strlen.c
>  create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/strncmp.c
>
> --
> 2.45.1
>