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SubjectRe: [PATCH 02/10] x86, asm: use bool for bitops and other assembly outputs
On Wed, Jun 08, 2016 at 02:31:31AM -0700, H. Peter Anvin wrote:
> On 06/08/16 02:20, Ingo Molnar wrote:
> >
> > Yeah, absolutely. I hate 'bool' with a vengence but if 'int' generates worse code
> > with modern compilers then I'm not going to argue for worse code. Would a 'char'
> > return type be very weird?
> >
>
> Yes. I have to admit I don't share your hatred for "bool" -- it gives
> the compiler a fairly crucial bit of information about what the possible
> values are for a certain piece of data.
>
> Upcasting to char loses that, and may case gcc to manifest the value as
> an integer instead of retaining it in the flags. It is, however, less
> likely to cause gcc to then try to widen the value to word size (which
> is an extra instruction on x86), but moving the value out of and back
> into the flags register is the big cost.

So I think using bool as return type or argument is fine, using it in
structures is 'insane'.

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