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List:       u-boot
Subject:    Re: [PATCH] arm: Use builtins for ffs/fls
From:       Sean Anderson <sean.anderson () seco ! com>
Date:       2023-07-31 21:48:09
Message-ID: cc3f16ca-a487-cdc5-5092-607c8bf338ca () seco ! com
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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
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