Re: [PATCH] x86: Align jump targets to 1 byte boundaries

From: Markus Trippelsdorf
Date: Sat Apr 11 2015 - 10:41:54 EST

On 2015.04.10 at 06:18 -0700, H. Peter Anvin wrote:
> On 04/10/2015 05:50 AM, Denys Vlasenko wrote:
> >
> > However, I'm an -Os guy. Expect -O2 people to disagree :)
> >
> The problem with -Os is that the compiler will make *any* tradeoffs to
> save a byte. It is really designed to squeeze as much code into a
> fixed-size chunk, e.g. a ROM, as possible.
> We have asked for an -Okernel mode from the gcc folks forever. It
> basically would mean "-Os except when really dumb."

If you want the best of both worlds perhaps you should reconsider Andy's
LTO patch? With -flto gcc automatically optimizes all functions that it
considers cold for size. So you could expect some code size savings even
with -O2 (or -O3).

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