Re: [PATCH v2 3/3] Add ffsl(), ffsll(), fls(), flsl(), flsll()

[Kito Cheng <kito dot cheng at gmail dot com>]

> Do you have plans to add RISC-V support to upstream Newlib?
Yes, I plan submit patches in next few weeks and I am doing testing
now, we have already porting to newlib 2.5[1].

> We should first investigate why GCC performs this optimization. The file is compiled with -fno-builtin, so it some other optimization. Maybe we need something like __attribute__ ((__optimize__ ("-fno-tree-loop-distribute-patterns"))) as in string/local.h.

-fno-builtin just mean do not emit any builtin function in front-end,
but we've explicit call builtin function here, so -fno-builtin doesn't
any help for this case.

However I think I could add a local ffs.c in libc/machine/riscv to
avoid this issue since I've saw it's really improve the code gen for
some target which have ffs or ctz instructions,
but the potential problem is maybe some target will hit this issue too.

[1] https://github.com/riscv/riscv-newlib