AArch64: Optimize memrchr

Optimize the main loop - large strings are 43% faster on modern CPUs.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>

diff --git a/sysdeps/aarch64/memrchr.S b/sysdeps/aarch64/memrchr.S
index 9d2d29a..621fc65 100644 (file)
--- a/sysdeps/aarch64/memrchr.S
+++ b/sysdeps/aarch64/memrchr.S
@@ -26,7 +26,6 @@
  * MTE compatible.
  */
 
-/* Arguments and results.  */
 #define srcin          x0
 #define chrin          w1
 #define cntin          x2
@@ -77,31 +76,34 @@ ENTRY (__memrchr)
        csel    result, result, xzr, hi
        ret
 
+       nop
 L(start_loop):
-       sub     tmp, end, src
-       subs    cntrem, cntin, tmp
+       subs    cntrem, src, srcin
        b.ls    L(nomatch)
 
        /* Make sure that it won't overread by a 16-byte chunk */
-       add     tmp, cntrem, 15
-       tbnz    tmp, 4, L(loop32_2)
+       sub     cntrem, cntrem, 1
+       tbz     cntrem, 4, L(loop32_2)
+       add     src, src, 16
 
-       .p2align 4
+       .p2align 5
 L(loop32):
-       ldr     qdata, [src, -16]!
+       ldr     qdata, [src, -32]!
        cmeq    vhas_chr.16b, vdata.16b, vrepchr.16b
        umaxp   vend.16b, vhas_chr.16b, vhas_chr.16b            /* 128->64 */
        fmov    synd, dend
        cbnz    synd, L(end)
 
 L(loop32_2):
-       ldr     qdata, [src, -16]!
+       ldr     qdata, [src, -16]
        subs    cntrem, cntrem, 32
        cmeq    vhas_chr.16b, vdata.16b, vrepchr.16b
-       b.ls    L(end)
+       b.lo    L(end_2)
        umaxp   vend.16b, vhas_chr.16b, vhas_chr.16b            /* 128->64 */
        fmov    synd, dend
        cbz     synd, L(loop32)
+L(end_2):
+       sub     src, src, 16
 L(end):
        shrn    vend.8b, vhas_chr.8h, 4         /* 128->64 */
        fmov    synd, dend