IIRC, at NetApp -O2 was the default for all builds. I think it is safe to
say that the generated code is quite stable. If -O2 allows the compiler to
catch errors earlier it should be the default.
-Kip
On 2/4/06, M. Warner Losh <[EMAIL PROTECTED]> wrote:
>
> In message: <[EMAIL PROTECTED]>
> [EMAIL PROTECTED] (Dag-Erling Smørgrav) writes:
> : Warner Losh <[EMAIL PROTECTED]> writes:
> : > Can we not have special flags for tinderbox builds? It make
> : > pre-commit testing a big pita. How about just -O on both head and
> : > in RELENG_6?
> :
> : As I have repeatedly pointed out in the past, -O2 catches more bugs
> : because it enables optimizations which require more extensive coverage
> : analysis.
>
> Then it should be the default, standard flag.
>
> : > The kernel make files have special magic to disable the parts of -O2
> : > that are known to be bad because tinderbox uses -O2, despite efforts
> : > in the past to stop the practice.
> :
> : The kernel has special magic to disable strict aliasing checks because
> : certain people regularly commit kernel code which violates C aliasing
> : rules and refuse to fix it. The userland code does not need these
> : hacks because I spent a lot of time and effort fixing aliasing bugs in
> : e.g. libalias.
>
> The optimizations are disable because they do not work. It is really
> that simple. The kernel has lots and lots of these problems, it is
> true.
>
> : Aliasing violations are not trivial matters; they prevent the compiler
> : from optimizing code which (for instance) accesses structure members
> : through pointers to the structure. There is a lot of this in the
> : kernel.
>
> I agree. However, I think it is unreasonable to have one set of
> defaults, then another set that committers are held to. This leads to
> lots of problems.
>
> My bottom line is that as a committer, you are expected to not break
> the builds with the default flags. The tinderbox runs at a different
> level, thereby creating the impression that someone has done something
> wrong when it happens to blow up, when in fact they have not. If -O2
> is so good w/o the -fno-strict-alias, then it should be the default so
> we catch these bugs.
>
> I'm not arguing against -O2 because it isn't useful. I'm arguing
> because it isn't the default.
>
> Warner
>
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