[PATCH v2] riscv: add RVV-optimized memchr

[daichengrong <daichengrong@iscas.ac.cn>]

This patch introduces an RVV based
implementation of memchr, leveraging vector instructions to
improve data-level parallelism.

The implementation has been tested on SG2044 (RVV 128-bit) and
Banana Pi F3 (RVV 256-bit) platforms.

Benchmark results show no observable regression on small inputs,
while providing significant performance improvements on larger
inputs.

If this approach proves effective, additional optimized mem/str
routines that have already been implemented and validated on
existing platforms, and demonstrate performance gains, will be
submitted in follow-up patches.

Signed-off-by: daichengrong <daichengrong@iscas.ac.cn>
---
 sysdeps/riscv/multiarch/memchr-generic.c      |  24 ++++
 sysdeps/riscv/multiarch/memchr-vector.S       |  26 ++++
 sysdeps/riscv/rvv/memchr.S                    | 128 ++++++++++++++++++
 .../unix/sysv/linux/riscv/multiarch/Makefile  |   3 +
 .../linux/riscv/multiarch/ifunc-impl-list.c   |   6 +
 .../unix/sysv/linux/riscv/multiarch/memchr.c  |  57 ++++++++
 6 files changed, 244 insertions(+)
 create mode 100644 sysdeps/riscv/multiarch/memchr-generic.c
 create mode 100644 sysdeps/riscv/multiarch/memchr-vector.S
 create mode 100644 sysdeps/riscv/rvv/memchr.S
 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..a95e16ee51
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memchr-generic.c
@@ -0,0 +1,24 @@
+/* Re-include the default memchr implementation.
+   Copyright (C) 2026 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
+# include <string/memchr.c>
+#endif
diff --git a/sysdeps/riscv/multiarch/memchr-vector.S b/sysdeps/riscv/multiarch/memchr-vector.S
new file mode 100644
index 0000000000..951f256245
--- /dev/null
+++ b/sysdeps/riscv/multiarch/memchr-vector.S
@@ -0,0 +1,26 @@
+/* Re-include the RISC-V RVV based memchr implementation.
+   Copyright (C) 2026 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)
+# define MEMCHR __memchr_vector
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name)
+# undef weak_alias
+# define weak_alias(name, alias)
+# include <sysdeps/riscv/rvv/memchr.S>
+#endif
diff --git a/sysdeps/riscv/rvv/memchr.S b/sysdeps/riscv/rvv/memchr.S
new file mode 100644
index 0000000000..2cdfeae0bf
--- /dev/null
+++ b/sysdeps/riscv/rvv/memchr.S
@@ -0,0 +1,128 @@
+/* RISC-V RVV based memchr.
+   Copyright (C) 2026 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 <sysdep.h>
+#include <sys/asm.h>
+
+#ifndef MEMCHR
+# define MEMCHR __memchr
+#endif
+
+#define srcin		a0
+#define chrin		a1
+#define cntin		a2
+#define result		a0
+
+#define src		    a0
+#define cntrem		a2
+#define cntrem_4    a5
+
+#define vdata		v0
+#define vmask		v16
+#define first_index a4
+
+#define	tmp         t0
+#define	vset_vl		t6
+
+#define src_2		a3
+#define src_3		a6
+#define src_4		a7
+
+#define vdata_1		v0
+#define vdata_2		v4
+#define vdata_3		v8
+#define vdata_4		v12
+
+#define vmask_1		v16
+#define vmask_2		v20
+#define vmask_3		v24
+#define vmask_4		v28
+
+#define first_index_1	a4
+#define first_index_2	t2
+#define first_index_3	t3
+#define first_index_4	t4
+
+ENTRY (MEMCHR)
+.option push
+.option arch, +v
+    beqz        cntin, L(ret)
+    and         tmp, cntin, 0x3F
+    beqz        tmp, L(loop_pre)
+    vsetvli     vset_vl, tmp, e8, m8, ta, ma
+    vle8.v      vdata, (srcin)
+    vmseq.vx    vmask, vdata, chrin
+    vfirst.m    first_index, vmask
+    bgez        first_index, L(found)
+
+    beq         vset_vl, cntin, L(ret)
+
+    add         src, srcin, vset_vl
+    sub         cntrem, cntin, vset_vl
+
+L(loop_pre):
+    srli        cntrem_4, cntrem, 2
+L(loop):
+    vsetvli     vset_vl, cntrem_4, e8, m4, ta, ma
+
+    vle8.v      vdata_1, (src)
+    add         src_2, src, vset_vl
+    vle8.v      vdata_2, (src_2)
+    add         src_3, src_2, vset_vl
+    vle8.v      vdata_3, (src_3)
+    add         src_4, src_3, vset_vl
+    vle8.v      vdata_4, (src_4)
+
+    vmseq.vx    vmask_1, vdata_1, chrin
+    vmseq.vx    vmask_2, vdata_2, chrin
+    vmseq.vx    vmask_3, vdata_3, chrin
+    vmseq.vx    vmask_4, vdata_4, chrin
+
+    vfirst.m    first_index, vmask_1
+    vfirst.m    first_index_2, vmask_2
+    vfirst.m    first_index_3, vmask_3
+    vfirst.m    first_index_4, vmask_4
+
+    bgez        first_index_1, L(found1)
+    bgez        first_index_2, L(found2)
+    bgez        first_index_3, L(found3)
+    bgez        first_index_4, L(found4)
+
+    add         src, src_4, vset_vl
+    sub         cntrem_4, cntrem_4, vset_vl
+    bnez        cntrem_4, L(loop)
+L(ret):
+    li          result, 0
+    ret
+L(found4):
+    add result, src_4, first_index_4
+    ret
+L(found3):
+    add result, src_3, first_index_3
+    ret
+L(found2):
+    add result, src_2, first_index_2
+    ret
+L(found1):
+L(found):
+    add result, src, first_index
+    ret
+.option pop
+END (MEMCHR)
+weak_alias (MEMCHR, memchr)
+libc_hidden_builtin_def (memchr)
diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
index 2a2b90960f..1e4061d7a6 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-vector \
   memcpy \
   memcpy-generic \
   memcpy-vector \
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 2501546665..02e891b6a5 100644
--- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
+++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
@@ -43,6 +43,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
       rvv_enabled = true;
   }
 
+  IFUNC_IMPL (i, name, memchr,
+	      IFUNC_IMPL_ADD (array, i, memchr, rvv_enabled,
+			      __memchr_vector)
+	      IFUNC_IMPL_ADD (array, i, memchr, 1, __memchr_generic))
+
+
   IFUNC_IMPL (i, name, memcpy,
 	      IFUNC_IMPL_ADD (array, i, memcpy, rvv_enabled,
 			      __memcpy_vector)
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..0844a33760
--- /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) 2026 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_vector 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_IMA_V) == RISCV_HWPROBE_IMA_V)
+    return __memchr_vector;
+  return __memchr_generic;
+}
+
+riscv_libc_ifunc (__libc_memchr, select_memchr_ifunc);
+
+# undef memchr
+strong_alias (__libc_memchr, memchr);
+strong_alias (memchr, __memchr)
+# ifdef SHARED
+__hidden_ver1 (memchr, __GI_memchr, __redirect_memchr)
+  __attribute__ ((visibility ("hidden"))) __attribute_copy__ (memchr);
+# endif
+#else
+# include <string/memchr.c>
+#endif
-- 
2.25.1