LoongArch: Add ifunc support for memrchr{lsx, lasx}

According to glibc memrchr microbenchmark, this implementation could reduce
the runtime as following:

Name            Percent of rutime reduced
memrchr-lasx    20%-83%
memrchr-lsx     20%-64%

7 files changed, 335 insertions, 0 deletions

diff --git a/sysdeps/loongarch/lp64/multiarch/Makefile b/sysdeps/loongarch/lp64/multiarch/Makefile
index 2f4802cfa4..7b87bc9055 100644
--- a/sysdeps/loongarch/lp64/multiarch/Makefile
+++ b/sysdeps/loongarch/lp64/multiarch/Makefile
@@ -27,5 +27,8 @@ sysdep_routines += \
   memchr-aligned \
   memchr-lsx \
   memchr-lasx \
+  memrchr-generic \
+  memrchr-lsx \
+  memrchr-lasx \
 # sysdep_routines
 endif
diff --git a/sysdeps/loongarch/lp64/multiarch/ifunc-impl-list.c b/sysdeps/loongarch/lp64/multiarch/ifunc-impl-list.c
index a567b9cf4d..8bd5489ee2 100644
--- a/sysdeps/loongarch/lp64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/loongarch/lp64/multiarch/ifunc-impl-list.c
@@ -109,5 +109,13 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 #endif
 	      IFUNC_IMPL_ADD (array, i, memchr, 1, __memchr_aligned)
 	      )
+
+  IFUNC_IMPL (i, name, memrchr,
+#if !defined __loongarch_soft_float
+	      IFUNC_IMPL_ADD (array, i, memrchr, SUPPORT_LASX, __memrchr_lasx)
+	      IFUNC_IMPL_ADD (array, i, memrchr, SUPPORT_LSX, __memrchr_lsx)
+#endif
+	      IFUNC_IMPL_ADD (array, i, memrchr, 1, __memrchr_generic)
+	      )
   return i;
 }
diff --git a/sysdeps/loongarch/lp64/multiarch/ifunc-memrchr.h b/sysdeps/loongarch/lp64/multiarch/ifunc-memrchr.h
new file mode 100644
index 0000000000..8215f9ad94
--- /dev/null
+++ b/sysdeps/loongarch/lp64/multiarch/ifunc-memrchr.h
@@ -0,0 +1,40 @@
+/* Common definition for memrchr implementation.
+   All versions must be listed in ifunc-impl-list.c.
+   Copyright (C) 2023 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 <ldsodefs.h>
+#include <ifunc-init.h>
+
+#if !defined __loongarch_soft_float
+extern __typeof (REDIRECT_NAME) OPTIMIZE (lasx) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (lsx) attribute_hidden;
+#endif
+extern __typeof (REDIRECT_NAME) OPTIMIZE (generic) attribute_hidden;
+
+static inline void *
+IFUNC_SELECTOR (void)
+{
+#if !defined __loongarch_soft_float
+  if (SUPPORT_LASX)
+    return OPTIMIZE (lasx);
+  else if (SUPPORT_LSX)
+    return OPTIMIZE (lsx);
+  else
+#endif
+    return OPTIMIZE (generic);
+}
diff --git a/sysdeps/loongarch/lp64/multiarch/memrchr-generic.c b/sysdeps/loongarch/lp64/multiarch/memrchr-generic.c
new file mode 100644
index 0000000000..ced61ebce5
--- /dev/null
+++ b/sysdeps/loongarch/lp64/multiarch/memrchr-generic.c
@@ -0,0 +1,23 @@
+/* Generic implementation of memrchr.
+   Copyright (C) 2023 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 MEMRCHR __memrchr_generic
+#endif
+
+#include <string/memrchr.c>
diff --git a/sysdeps/loongarch/lp64/multiarch/memrchr-lasx.S b/sysdeps/loongarch/lp64/multiarch/memrchr-lasx.S
new file mode 100644
index 0000000000..5f3e0d06d7
--- /dev/null
+++ b/sysdeps/loongarch/lp64/multiarch/memrchr-lasx.S
@@ -0,0 +1,123 @@
+/* Optimized memrchr implementation using LoongArch LASX instructions.
+   Copyright (C) 2023 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/regdef.h>
+#include <sys/asm.h>
+
+#if IS_IN (libc) && !defined __loongarch_soft_float
+
+#ifndef MEMRCHR
+# define MEMRCHR __memrchr_lasx
+#endif
+
+LEAF(MEMRCHR, 6)
+    beqz            a2, L(ret0)
+    addi.d          a2, a2, -1
+    add.d           a3, a0, a2
+    andi            t1, a3, 0x3f
+
+    bstrins.d       a3, zero, 5, 0
+    addi.d          t1, t1, 1
+    xvld            xr0, a3, 0
+    xvld            xr1, a3, 32
+
+    sub.d           t2, zero, t1
+    li.d            t3, -1
+    xvreplgr2vr.b   xr2, a1
+    andi            t4, a0, 0x3f
+
+    srl.d           t2, t3, t2
+    xvseq.b         xr0, xr0, xr2
+    xvseq.b         xr1, xr1, xr2
+    xvmsknz.b       xr0, xr0
+
+
+    xvmsknz.b       xr1, xr1
+    xvpickve.w      xr3, xr0, 4
+    xvpickve.w      xr4, xr1, 4
+    vilvl.h         vr0, vr3, vr0
+
+    vilvl.h         vr1, vr4, vr1
+    vilvl.w         vr0, vr1, vr0
+    movfr2gr.d      t0, fa0
+    and             t0, t0, t2
+
+    bltu            a2, t1, L(end)
+    bnez            t0, L(found)
+    bstrins.d       a0, zero, 5, 0
+L(loop):
+    xvld            xr0, a3, -64
+
+    xvld            xr1, a3, -32
+    addi.d          a3, a3, -64
+    xvseq.b         xr0, xr0, xr2
+    xvseq.b         xr1, xr1, xr2
+
+
+    beq             a0, a3, L(out)
+    xvmax.bu        xr3, xr0, xr1
+    xvseteqz.v      fcc0, xr3
+    bcnez           fcc0, L(loop)
+
+    xvmsknz.b       xr0, xr0
+    xvmsknz.b       xr1, xr1
+    xvpickve.w      xr3, xr0, 4
+    xvpickve.w      xr4, xr1, 4
+
+    vilvl.h         vr0, vr3, vr0
+    vilvl.h         vr1, vr4, vr1
+    vilvl.w         vr0, vr1, vr0
+    movfr2gr.d      t0, fa0
+
+L(found):
+    addi.d          a0, a3, 63
+    clz.d           t1, t0
+    sub.d           a0, a0, t1
+    jr              ra
+
+
+L(out):
+    xvmsknz.b       xr0, xr0
+    xvmsknz.b       xr1, xr1
+    xvpickve.w      xr3, xr0, 4
+    xvpickve.w      xr4, xr1, 4
+
+    vilvl.h         vr0, vr3, vr0
+    vilvl.h         vr1, vr4, vr1
+    vilvl.w         vr0, vr1, vr0
+    movfr2gr.d      t0, fa0
+
+L(end):
+    sll.d           t2, t3, t4
+    and             t0, t0, t2
+    addi.d          a0, a3, 63
+    clz.d           t1, t0
+
+    sub.d           a0, a0, t1
+    maskeqz         a0, a0, t0
+    jr              ra
+L(ret0):
+    move            a0, zero
+
+
+    jr              ra
+END(MEMRCHR)
+
+libc_hidden_builtin_def (MEMRCHR)
+#endif
diff --git a/sysdeps/loongarch/lp64/multiarch/memrchr-lsx.S b/sysdeps/loongarch/lp64/multiarch/memrchr-lsx.S
new file mode 100644
index 0000000000..39a7c8b076
--- /dev/null
+++ b/sysdeps/loongarch/lp64/multiarch/memrchr-lsx.S
@@ -0,0 +1,105 @@
+/* Optimized memrchr implementation using LoongArch LSX instructions.
+   Copyright (C) 2023 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/regdef.h>
+#include <sys/asm.h>
+
+#if IS_IN (libc) && !defined __loongarch_soft_float
+
+# define MEMRCHR __memrchr_lsx
+
+LEAF(MEMRCHR, 6)
+    beqz            a2, L(ret0)
+    addi.d          a2, a2, -1
+    add.d           a3, a0, a2
+    andi            t1, a3, 0x1f
+
+    bstrins.d       a3, zero, 4, 0
+    addi.d          t1, t1, 1
+    vld             vr0, a3, 0
+    vld             vr1, a3, 16
+
+    sub.d           t2, zero, t1
+    li.d            t3, -1
+    vreplgr2vr.b    vr2, a1
+    andi            t4, a0, 0x1f
+
+    srl.d           t2, t3, t2
+    vseq.b          vr0, vr0, vr2
+    vseq.b          vr1, vr1, vr2
+    vmsknz.b        vr0, vr0
+
+
+    vmsknz.b        vr1, vr1
+    vilvl.h         vr0, vr1, vr0
+    movfr2gr.s      t0, fa0
+    and             t0, t0, t2
+
+    bltu            a2, t1, L(end)
+    bnez            t0, L(found)
+    bstrins.d       a0, zero, 4, 0
+L(loop):
+    vld             vr0, a3, -32
+
+    vld             vr1, a3, -16
+    addi.d          a3, a3, -32
+    vseq.b          vr0, vr0, vr2
+    vseq.b          vr1, vr1, vr2
+
+    beq             a0, a3, L(out)
+    vmax.bu         vr3, vr0, vr1
+    vseteqz.v       fcc0, vr3
+    bcnez           fcc0, L(loop)
+
+
+    vmsknz.b        vr0, vr0
+    vmsknz.b        vr1, vr1
+    vilvl.h         vr0, vr1, vr0
+    movfr2gr.s      t0, fa0
+
+L(found):
+    addi.d          a0, a3, 31
+    clz.w           t1, t0
+    sub.d           a0, a0, t1
+    jr              ra
+
+L(out):
+    vmsknz.b        vr0, vr0
+    vmsknz.b        vr1, vr1
+    vilvl.h         vr0, vr1, vr0
+    movfr2gr.s      t0, fa0
+
+L(end):
+    sll.d           t2, t3, t4
+    and             t0, t0, t2
+    addi.d          a0, a3, 31
+    clz.w           t1, t0
+
+
+    sub.d           a0, a0, t1
+    maskeqz         a0, a0, t0
+    jr              ra
+L(ret0):
+    move            a0, zero
+
+    jr              ra
+END(MEMRCHR)
+
+libc_hidden_builtin_def (MEMRCHR)
+#endif
diff --git a/sysdeps/loongarch/lp64/multiarch/memrchr.c b/sysdeps/loongarch/lp64/multiarch/memrchr.c
new file mode 100644
index 0000000000..8baba9ab7e
--- /dev/null
+++ b/sysdeps/loongarch/lp64/multiarch/memrchr.c
@@ -0,0 +1,33 @@
+/* Multiple versions of memrchr.
+   All versions must be listed in ifunc-impl-list.c.
+   Copyright (C) 2023 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/>.  */
+
+/* Define multiple versions only for the definition in libc.  */
+#if IS_IN (libc)
+# define memrchr __redirect_memrchr
+# include <string.h>
+# undef memrchr
+
+# define SYMBOL_NAME memrchr
+# include "ifunc-memrchr.h"
+
+libc_ifunc_redirected (__redirect_memrchr, __memrchr, IFUNC_SELECTOR ());
+libc_hidden_def (__memrchr)
+weak_alias (__memrchr, memrchr)
+
+#endif