Messages in this thread | | | Date | Mon, 26 Sep 2022 11:30:14 -0700 | From | Kees Cook <> | Subject | Re: [PATCH v3 2/2] minmax: clamp more efficiently by avoiding extra comparison |
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On Mon, Sep 26, 2022 at 03:34:35PM +0200, Jason A. Donenfeld wrote: > [...] > In this case, we actually gain a branch, unfortunately, because the > compiler's replacement axioms no longer as cleanly apply. > > So all and all, this change is a bit of a mixed bag.
I'm on the fence -- I think the new macro is a more correct way to describe the operation, though on the other hand, the old way provides a simple way to compose the bounds checks.
I suspect we should probably optimize for _performance_, not code size, so if the new branch is actually visible via cycle counts in "perf" output, probably we shouldn't use this patch, and instead add a comment about why it is defined the way it is.
-Kees
-- Kees Cook
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