[PATCH 5/6] riscv: add vectorized memrchr

The vector implementation processes data in vector-length chunks,
providing significant performance improvements on RVV-capable hardware.
Use conditional compilation to fall back to the scalar implementation
when __riscv_vector is not available, maintaining compatibility with
non-vector RISC-V systems.

Signed-off-by: Pincheng Wang <[email protected]>
---
 newlib/libc/machine/riscv/Makefile.inc  |  1 +
 newlib/libc/machine/riscv/memrchr-asm.S | 40 +++++++++++++++++++++++++
 newlib/libc/machine/riscv/memrchr.c     |  4 +++
 3 files changed, 45 insertions(+)
 create mode 100644 newlib/libc/machine/riscv/memrchr-asm.S

diff --git a/newlib/libc/machine/riscv/Makefile.inc b/newlib/libc/machine/riscv/Makefile.inc
index 14134d7ba..086150e45 100644
--- a/newlib/libc/machine/riscv/Makefile.inc
+++ b/newlib/libc/machine/riscv/Makefile.inc
@@ -13,6 +13,7 @@ libc_a_SOURCES += \
         %D%/memmove.c \
         %D%/mempcpy-asm.S \
         %D%/mempcpy.c \
+        %D%/memrchr-asm.S \
         %D%/memrchr.c \
         %D%/memset.S \
         %D%/setjmp.S \
diff --git a/newlib/libc/machine/riscv/memrchr-asm.S b/newlib/libc/machine/riscv/memrchr-asm.S
new file mode 100644
index 000000000..a83061547
--- /dev/null
+++ b/newlib/libc/machine/riscv/memrchr-asm.S
@@ -0,0 +1,40 @@
+#if defined(__riscv_vector) && !defined(__OPTIMIZE_SIZE__) && !defined(PREFER_SIZE_OVER_SPEED)
+.text
+.option push
+.option arch, +zve32x
+.global memrchr
+.type memrchr, @function
+memrchr:
+#if __riscv_landing_pad
+  lpad 0
+#endif
+  andi a1, a1, 0xff
+  add a0, a0, a2
+.Lloop:
+  beqz a2, .Lnohit
+
+  vsetvli a3, a2, e8, m4, ta, ma
+  sub a0, a0, a3
+  vle8.v v8, (a0)
+  sub a2, a2, a3
+
+  vmseq.vx v0, v8, a1
+  vfirst.m a4, v0
+  bltz a4, .Lloop
+
+  vsetvli zero, a3, e16, m8, ta, ma
+  vid.v v16
+
+  /* Reduce max index over hit lanes.  */
+  vmv.s.x v24, x0
+  vredmaxu.vs v24, v16, v24, v0.t
+  vmv.x.s a5, v24
+
+  add a0, a0, a5
+  ret
+.Lnohit:
+  li a0, 0
+  ret
+.size memrchr, .-memrchr
+.option pop
+#endif
diff --git a/newlib/libc/machine/riscv/memrchr.c b/newlib/libc/machine/riscv/memrchr.c
index 47e10238a..ddfe60816 100644
--- a/newlib/libc/machine/riscv/memrchr.c
+++ b/newlib/libc/machine/riscv/memrchr.c
@@ -28,6 +28,9 @@ PORTABILITY
 QUICKREF
 	memrchr
 */
+#if defined(__riscv_vector) && !defined(__OPTIMIZE_SIZE__) && !defined(PREFER_SIZE_OVER_SPEED)
+/* memrchr defined in memrchr-asm.S */
+#else
 
 #include <sys/asm.h>
 #include <stddef.h>
@@ -170,3 +173,4 @@ memrchr (const void *src_void,
 
   return NULL;
 }
+#endif
-- 
2.39.5