From: > Peter Zijlstra
> Sent: 18 March 2019 15:39
>
> With CONFIG_PROFILE_ALL_BRANCHES, the "if" macro converts the
> conditional to an array index. This can cause GCC to create horrible
> code. When there are nested ifs, the generated code uses register
> values to encode branching decisions.
>
> Make it easier for GCC to optimize by keeping the conditional as a
> conditional rather than converting it to an integer. This shrinks the
> generated code quite a bit, and also makes the code sane enough for
> objtool to understand.
...
> include/linux/compiler.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_
> .line = __LINE__, \
> }; \
> ______r = !!(cond); \
Is that (or maybe just the !!) needed any more??
> - ______f.miss_hit[______r]++;
> \
> + ______r ? ______f.miss_hit[1]++ : ______f.miss_hit[0]++;\
> ______r; \
> }))
> #endif /* CONFIG_PROFILE_ALL_BRANCHES */
>
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)
