[PATCH] arm: memset: zero out upper bytes in r1
a.ryabinin at samsung.com
Thu May 8 07:40:31 PDT 2014
On 05/08/14 11:59, Andrey Ryabinin wrote:
> On 05/08/14 03:42, Afzal Mohammed wrote:
>> int is to be converted to unsigned char in memset, would having above
>> change immediately upon entry to memset rather than at a place where it
>> won't always execute make intention clearer ? (although it doesn't make
> I think it's better to keep it near other manipulations with r1.
> Plus this will save us from executing extra instruction on 'memset -> 6 -> 5 -> return'
> path (memset for size <= 3).
>> ubfx r1, r1, #0, #8 would have given the needed typecasting, but seems
>> it is available only on ARMv6T2 & above.
> Indeed. It might be wrapped it with #if #else, but it will be a bit ugly,
> probably not worth to do.
Err, there is no reason to use ubfx, it just the same as and r1,r1, #0xff.
On ARMv6T2 & above one instruction could be saved by using BFI instead of ORR, like this:
diff --git a/arch/arm/lib/memset.S b/arch/arm/lib/memset.S
index 94b0650..9a7f714 100644
@@ -22,8 +22,8 @@ ENTRY(memset)
* we know that the pointer in ip is aligned to a word boundary.
-1: orr r1, r1, r1, lsl #8
- orr r1, r1, r1, lsl #16
+1: bfi r1, r1, #8, #8
+ bfi r1, r1, #16, #16
mov r3, r1
cmp r2, #16
More information about the linux-arm-kernel