RISC-V: improve string-function assembly

Adapt the suggestions for the assembly string functions that Andrew
suggested but that I didn't manage to include into the series that
got applied.

This includes improvements to two comments, removal of unneeded labels
and moving one instruction slightly higher to contradict an
explanatory comment.

Suggested-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230208225328.1636017-3-heiko@sntech.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
index 986ab23..c42a841 100644 (file)
--- a/arch/riscv/lib/strcmp.S
+++ b/arch/riscv/lib/strcmp.S
@@ -40,7 +40,9 @@ SYM_FUNC_START(strcmp)
        ret
 
 /*
- * Variant of strcmp using the ZBB extension if available
+ * Variant of strcmp using the ZBB extension if available.
+ * The code was published as part of the bitmanip manual
+ * in Appendix A.
  */
 #ifdef CONFIG_RISCV_ISA_ZBB
 strcmp_zbb:
@@ -57,7 +59,7 @@ strcmp_zbb:
         *   a1 - string2
         *
         * Clobbers
-        *   t0, t1, t2, t3, t4, t5
+        *   t0, t1, t2, t3, t4
         */
 
        or      t2, a0, a1

diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
index 8345cee..15bb8f3 100644 (file)
--- a/arch/riscv/lib/strlen.S
+++ b/arch/riscv/lib/strlen.S
@@ -96,7 +96,7 @@ strlen_zbb:
         * of valid bytes in this chunk.
         */
        srli    a0, t1, 3
-       bgtu    t3, a0, 3f
+       bgtu    t3, a0, 2f
 
        /* Prepare for the word comparison loop. */
        addi    t2, t0, SZREG
@@ -112,20 +112,20 @@ strlen_zbb:
        addi    t0, t0, SZREG
        orc.b   t1, t1
        beq     t1, t3, 1b
-2:
+
        not     t1, t1
        CZ      t1, t1
+       srli    t1, t1, 3
 
-       /* Get number of processed words.  */
+       /* Get number of processed bytes. */
        sub     t2, t0, t2
 
        /* Add number of characters in the first word.  */
        add     a0, a0, t2
-       srli    t1, t1, 3
 
        /* Add number of characters in the last word.  */
        add     a0, a0, t1
-3:
+2:
        ret
 
 .option pop

diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
index ee49595..e09de79 100644 (file)
--- a/arch/riscv/lib/strncmp.S
+++ b/arch/riscv/lib/strncmp.S
@@ -70,7 +70,7 @@ strncmp_zbb:
        li      t5, -1
        and     t2, t2, SZREG-1
        add     t4, a0, a2
-       bnez    t2, 4f
+       bnez    t2, 3f
 
        /* Adjust limit for fast-path.  */
        andi    t6, t4, -SZREG
@@ -114,23 +114,21 @@ strncmp_zbb:
        ret
 
        /* Simple loop for misaligned strings.  */
-3:
-       /* Restore limit for slow-path.  */
        .p2align 3
-4:
-       bge     a0, t4, 6f
+3:
+       bge     a0, t4, 5f
        lbu     t0, 0(a0)
        lbu     t1, 0(a1)
        addi    a0, a0, 1
        addi    a1, a1, 1
-       bne     t0, t1, 5f
-       bnez    t0, 4b
+       bne     t0, t1, 4f
+       bnez    t0, 3b
 
-5:
+4:
        sub     a0, t0, t1
        ret
 
-6:
+5:
        li      a0, 0
        ret