[PATCH 3/7] RISC-V: Add Zbb optimized memrchr as ifunc

["Christoph Müllner" <christoph.muellner@vrull.eu>]

When building with Zbb enabled, memrchr benefits from using orc.b in
find_zero_all().  This patch changes the build system such, that a
non-Zbb version as well as a Zbb version of this routine is built.
Further, a ifunc resolver is provided that selects the right routine
based on the outcome of extension probing via hwprobe().

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
---
 sysdeps/riscv/multiarch/memrchr-generic.c     | 26 ++++++++
 sysdeps/riscv/multiarch/memrchr-zbb.c         | 30 +++++++++
 .../unix/sysv/linux/riscv/multiarch/Makefile  |  3 +
 .../linux/riscv/multiarch/ifunc-impl-list.c   |  4 ++
 .../unix/sysv/linux/riscv/multiarch/memrchr.c | 61 +++++++++++++++++++
 5 files changed, 124 insertions(+)
 create mode 100644 sysdeps/riscv/multiarch/memrchr-generic.c
 create mode 100644 sysdeps/riscv/multiarch/memrchr-zbb.c
 create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/memrchr.c

diff --git a/sysdeps/riscv/multiarch/memrchr-generic.c b/sysdeps/riscv/multiarch/memrchr-generic.c
new file mode 100644
index 0000000000..7c1286cb60
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memrchr-generic.c
@@ -0,0 +1,26 @@
+/* Re-include the default memrchr implementation.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <string.h>
+
+#if IS_IN(libc)
+# define MEMRCHR __memrchr_generic
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(x)
+#endif
+#include <string/memrchr.c>
diff --git a/sysdeps/riscv/multiarch/memrchr-zbb.c b/sysdeps/riscv/multiarch/memrchr-zbb.c
new file mode 100644
index 0000000000..c074c7607c
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memrchr-zbb.c
@@ -0,0 +1,30 @@
+/* Re-include the default memrchr implementation for Zbb.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <string.h>
+
+#if IS_IN(libc)
+# define MEMRCHR __memrchr_zbb
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(x)
+#endif
+/* Convince preprocessor to have Zbb instructions.  */
+#ifndef __riscv_zbb
+# define __riscv_zbb
+#endif
+#include <string/memrchr.c>
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index 5586d11c89..d36d0bd6dd 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -6,6 +6,9 @@ sysdep_routines += \
   memcpy \
   memcpy-generic \
   memcpy_noalignment \
+  memrchr \
+  memrchr-generic \
+  memrchr-zbb \
   # sysdep_routines
 
 CFLAGS-memcpy_noalignment.c += -mno-strict-align
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
index 7321144a32..f4ec58b9d8 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -60,5 +60,9 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __memcpy_noalignment)
 	      IFUNC_IMPL_ADD (array, i, memcpy, 1, __memcpy_generic))
 
+  IFUNC_IMPL (i, name, memrchr,
+	      IFUNC_IMPL_ADD (array, i, memrchr, has_zbb, __memrchr_zbb)
+	      IFUNC_IMPL_ADD (array, i, memrchr, 1, __memrchr_generic))
+
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/memrchr.c b/sysdeps/unix/sysv/linux/riscv/multiarch/memrchr.c
new file mode 100644
index 0000000000..e19ac471c1
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/memrchr.c
@@ -0,0 +1,61 @@
+/* Multiple versions of memrchr.
+   All versions must be listed in ifunc-impl-list.c.
+   Copyright (C) 2017-2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#if IS_IN (libc)
+/* Redefine memrchr so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef memrchr
+# undef __memrchr
+# define memrchr __redirect_memrchr
+# define __memrchr __redirect___memrchr
+# include <stdint.h>
+# include <string.h>
+# include <ifunc-init.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (__redirect_memrchr) __libc_memrchr;
+
+extern __typeof (__redirect_memrchr) __memrchr_generic attribute_hidden;
+extern __typeof (__redirect_memrchr) __memrchr_zbb attribute_hidden;
+
+static inline __typeof (__redirect_memrchr) *
+select_memrchr_ifunc (uint64_t dl_hwcap, __riscv_hwprobe_t hwprobe_func)
+{
+  unsigned long long int v;
+  if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_IMA_EXT_0, &v) == 0
+      && (v & RISCV_HWPROBE_EXT_ZBB))
+    return __memrchr_zbb;
+
+  return __memrchr_generic;
+}
+
+riscv_libc_ifunc (__libc_memrchr, select_memrchr_ifunc);
+
+# undef memrchr
+# undef __memrchr
+strong_alias (__libc_memrchr, __memrchr);
+weak_alias (__memrchr, memrchr)
+# ifdef SHARED
+__hidden_ver1 (memrchr, __GI___memrchr, __redirect_memrchr)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (memrchr);
+# endif
+#else
+# include <string/memrchr.c>
+#endif
-- 
2.44.0