Re: [PATCH] arm: Use builtins for ffs/fls

On 7/31/23 17:27, 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@seco.com

I only tested this on ARMv8. If someone has an ARMv5 or ARMv6 board, please test this.

+CC Linus since he may care about integrator.

--Sean