[PATCH] arm: Use builtins for ffs/fls

Sean Anderson sean.anderson at seco.com
Mon Jul 31 23:42:07 CEST 2023

On 7/31/23 17:36, Tom Rini wrote:
> On Mon, Jul 31, 2023 at 05:27:33PM -0400, Sean Anderson wrote:
>> Since ARMv5, the clz instruction allows for efficient implementation of
>> ffs/fls with builtins. Until ARMv7 (with Thumb-2), this instruction is
>> only available in ARM mode. LTO makes it difficult to force specific
>> functions to be in ARM mode, as it is effectively a form of very
>> aggressive inlining. To work around this, fls/ffs are implemented in
>> assembly for ARMv5 and ARMv6 when compiling U-Boot in Thumb mode.
>> Overall, this saves around 75 bytes per call.
>> Signed-off-by: Sean Anderson <sean.anderson at seco.com>
> This looks like it's synced from the kernel, what tag?

The builtins are synced from v5.15 and they haven't changed since.


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