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    SubjectRe: [PATCH 1/3] Fix Unlikely(x) == y
    On Mon, Feb 18, 2008 at 03:01:35PM +0100, Geert Uytterhoeven wrote:
    > On Mon, 18 Feb 2008, Adrian Bunk wrote:
    > >
    > > This means it generates faster code with a current gcc for your platform.
    > >
    > > But a future gcc might e.g. replace the whole loop with a division
    > > (gcc SVN head (that will soon become gcc 4.3) already does
    > > transformations like replacing loops with divisions [1]).
    >
    > Hence shouldn't we ask the gcc people what's the purpose of __builtin_expect(),
    > if it doesn't live up to its promise?

    That's a different issue.

    My point here is that we do not know how the latest gcc available in the
    year 2010 might transform this code, and how a likely/unlikely placed
    there might influence gcc's optimizations then.

    If this is in hotpath code with a measurable speedup when using
    likely/unlikely with a current gcc then it's worth it.

    But otherwise it brings no real advantage today and the longterm effects
    are not predictable.

    > With kind regards,
    >
    > Geert Uytterhoeven

    cu
    Adrian

    --

    "Is there not promise of rain?" Ling Tan asked suddenly out
    of the darkness. There had been need of rain for many days.
    "Only a promise," Lao Er said.
    Pearl S. Buck - Dragon Seed



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