[PATCH 2/7] RISC-V: Add Zbb optimized memchr as ifunc

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

When building with Zbb enabled, memchr 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/memchr-generic.c      | 26 +++++++++
 sysdeps/riscv/multiarch/memchr-zbb.c          | 30 ++++++++++
 .../unix/sysv/linux/riscv/multiarch/Makefile  |  3 +
 .../linux/riscv/multiarch/ifunc-impl-list.c   | 31 ++++++++--
 .../unix/sysv/linux/riscv/multiarch/memchr.c  | 57 +++++++++++++++++++
 5 files changed, 142 insertions(+), 5 deletions(-)
 create mode 100644 sysdeps/riscv/multiarch/memchr-generic.c
 create mode 100644 sysdeps/riscv/multiarch/memchr-zbb.c
 create mode 100644 sysdeps/unix/sysv/linux/riscv/multiarch/memchr.c

diff --git a/sysdeps/riscv/multiarch/memchr-generic.c b/sysdeps/riscv/multiarch/memchr-generic.c
new file mode 100644
index 0000000000..a96c36398b
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memchr-generic.c
@@ -0,0 +1,26 @@
+/* Re-include the default memchr 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 MEMCHR __memchr_generic
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(x)
+#endif
+#include <string/memchr.c>
diff --git a/sysdeps/riscv/multiarch/memchr-zbb.c b/sysdeps/riscv/multiarch/memchr-zbb.c
new file mode 100644
index 0000000000..bead0335ae
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memchr-zbb.c
@@ -0,0 +1,30 @@
+/* Re-include the default memchr 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 MEMCHR __memchr_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/memchr.c>
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index fcef5659d4..5586d11c89 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
@@ -1,5 +1,8 @@
 ifeq ($(subdir),string)
 sysdep_routines += \
+  memchr \
+  memchr-generic \
+  memchr-zbb \
   memcpy \
   memcpy-generic \
   memcpy_noalignment \
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 9f806d7a9e..7321144a32 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -20,19 +20,40 @@
 #include <string.h>
 #include <sys/hwprobe.h>
 
+#define ARRAY_SIZE(A) (sizeof (A) / sizeof ((A)[0]))
+
 size_t
 __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			size_t max)
 {
   size_t i = max;
+  struct riscv_hwprobe pairs[] = {
+    { .key = RISCV_HWPROBE_KEY_IMA_EXT_0 },
+    { .key = RISCV_HWPROBE_KEY_CPUPERF_0 },
+  };
 
+  bool has_zbb = false;
   bool fast_unaligned = false;
 
-  struct riscv_hwprobe pair = { .key = RISCV_HWPROBE_KEY_CPUPERF_0 };
-  if (__riscv_hwprobe (&pair, 1, 0, NULL, 0) == 0
-      && (pair.value & RISCV_HWPROBE_MISALIGNED_MASK)
-          == RISCV_HWPROBE_MISALIGNED_FAST)
-    fast_unaligned = true;
+  if (__riscv_hwprobe (pairs, ARRAY_SIZE (pairs), 0, NULL, 0) == 0)
+    {
+      struct riscv_hwprobe *pair;
+
+      /* RISCV_HWPROBE_KEY_IMA_EXT_0  */
+      pair = &pairs[0];
+      if (pair->value & RISCV_HWPROBE_EXT_ZBB)
+        has_zbb = true;
+
+      /* RISCV_HWPROBE_KEY_CPUPERF_0  */
+      pair = &pairs[1];
+      if ((pair->value & RISCV_HWPROBE_MISALIGNED_MASK)
+	   == RISCV_HWPROBE_MISALIGNED_FAST)
+        fast_unaligned = true;
+    }
+
+  IFUNC_IMPL (i, name, memchr,
+	      IFUNC_IMPL_ADD (array, i, memchr, has_zbb, __memchr_zbb)
+	      IFUNC_IMPL_ADD (array, i, memchr, 1, __memchr_generic))
 
   IFUNC_IMPL (i, name, memcpy,
 	      IFUNC_IMPL_ADD (array, i, memcpy, fast_unaligned,
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/memchr.c b/sysdeps/unix/sysv/linux/riscv/multiarch/memchr.c
new file mode 100644
index 0000000000..bc076cbf24
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/memchr.c
@@ -0,0 +1,57 @@
+/* Multiple versions of memchr.
+   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 memchr so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef memchr
+# define memchr __redirect_memchr
+# include <stdint.h>
+# include <string.h>
+# include <ifunc-init.h>
+# include <riscv-ifunc.h>
+# include <sys/hwprobe.h>
+
+extern __typeof (__redirect_memchr) __libc_memchr;
+
+extern __typeof (__redirect_memchr) __memchr_generic attribute_hidden;
+extern __typeof (__redirect_memchr) __memchr_zbb attribute_hidden;
+
+static inline __typeof (__redirect_memchr) *
+select_memchr_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 __memchr_zbb;
+
+  return __memchr_generic;
+}
+
+riscv_libc_ifunc (__libc_memchr, select_memchr_ifunc);
+
+# undef memchr
+strong_alias (__libc_memchr, memchr);
+# ifdef SHARED
+__hidden_ver1 (memchr, __GI_memchr, __redirect_memchr)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (memchr);
+# endif
+#else
+# include <string/memchr.c>
+#endif
-- 
2.44.0