On Tue, 2 Jan 2007, Adrian Bunk wrote:
>
> My point is that we have several reported problems only visible
> with gcc 4.1.
>
> Other bug reports are e.g. [2] and [3], but they are only present with
> using gcc 4.1 _and_ using -Os.
Traditionally, afaik, -Os has tended to show compiler problems that
_could_ happen with -O2 too, but never do in practice. It may be that
gcc-4.1 without -Os miscompiles some very unusual code, and then with -Os
we just hit more cases of that.
That said, I th ink gcc-4.1.1 is very common - I know it's the Fedora
compiler. Also, CC_OPTIMIZE_FOR_SIZE defaults to 'y' if you have
EXPERIMENTAL on, and from all the bug-reports about other features that
are marked EXPERIMENTAL, I know that a lot of people do seem to select for
it. So I would expect that gcc-4.1.1 and -Os is actually a fairly common
combination. I just checked, and it's what I use personally, for example.
Of course, my main machine is an x86-64, and it has more registers. At
least some historical -Os bug was about bad things happening under
register pressure, iirc, and so x86-64 would show fewer problems than
regular 32-bit x86 (which has far fewer registers for the compiler to
use).
It is a bit worrisome. These things seem to be about 50:50 real kernel
bugs (just hidden by some common code generation sequence) and real
honest-to-goodness compiler bugs. But they are hard as hell to find.
Linus
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