[src/trunk]: src/sys/arch/alpha/alpha Re-arrange alpha_copystr() so that the ...

[thorpej <thorpej%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/3e3fa2ddd6b9
branches:  trunk
changeset: 1022172:3e3fa2ddd6b9
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Wed Jul 07 02:44:04 2021 +0000

description:
Re-arrange alpha_copystr() so that the the error/unlikely cases are forward
branches (which will be predicted as not-taken), and that the likely cases
are fall-through, with the exception of the loop branch (which is a backward
branch, and thus will be predicted as taken).

diffstat:

 sys/arch/alpha/alpha/locore.s |  19 ++++++++++---------
 1 files changed, 10 insertions(+), 9 deletions(-)

diffs (56 lines):

diff -r 4af61aef53a3 -r 3e3fa2ddd6b9 sys/arch/alpha/alpha/locore.s
--- a/sys/arch/alpha/alpha/locore.s     Tue Jul 06 21:41:36 2021 +0000
+++ b/sys/arch/alpha/alpha/locore.s     Wed Jul 07 02:44:04 2021 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: locore.s,v 1.137 2021/05/23 01:00:53 thorpej Exp $ */
+/* $NetBSD: locore.s,v 1.138 2021/07/07 02:44:04 thorpej Exp $ */
 
 /*-
  * Copyright (c) 1999, 2000, 2019 The NetBSD Foundation, Inc.
@@ -67,7 +67,7 @@
 
 #include <machine/asm.h>
 
-__KERNEL_RCSID(0, "$NetBSD: locore.s,v 1.137 2021/05/23 01:00:53 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: locore.s,v 1.138 2021/07/07 02:44:04 thorpej Exp $");
 
 #include "assym.h"
 
@@ -900,15 +900,13 @@
 /**************************************************************************/
 
 /*
- * XXX XXX XXX: Should be removed?
+ * alpha_copystr(const void *from, void *to, size_t len, size_t *donep)
  */
 LEAF(alpha_copystr, 4)
        LDGP(pv)
 
        mov     a2, t0                  /* t0 = i = len */
-       bne     a2, 1f                  /* if (len != 0), proceed */
-       ldiq    t1, 1                   /* else bail */
-       br      zero, 2f
+       beq     a2, 5f                  /* if (len == 0), bail */
 
 1:     ldq_u   t1, 0(a0)               /* t1 = *from */
        extbl   t1, a0, t1
@@ -927,13 +925,16 @@
 2:     beq     a3, 3f                  /* if (lenp != NULL) */
        subl    t0, a2, t0              /* *lenp = (i - len) */
        stq     t0, 0(a3)
-3:     beq     t1, 4f                  /* *from == '\0'; leave quietly */
+3:     bne     t1, 4f                  /* *from != '\0'; leave in a huff */
 
-       ldiq    v0, ENAMETOOLONG        /* *from != '\0'; error. */
+       mov     zero, v0                /* return 0. */
        RET
 
-4:     mov     zero, v0                /* return 0. */
+4:     ldiq    v0, ENAMETOOLONG
        RET
+
+5:     ldiq    t1, 1                   /* fool the test above... */
+       br      zero, 2b
        END(alpha_copystr)
 
 NESTED(copyinstr, 4, 16, ra, IM_RA|IM_S0, 0)