On Wednesday 16 of May 2012, Stephan Bergmann wrote:
On 05/16/2012 03:09 PM, Lubos Lunak wrote:
Now --enable-debug=-sc/ means that sc/ is built without -g and with
-O2. In other words, the compiler spends extra time working on code I
don't care about at all. There was a reason why OPT flags was empty in
--enable-debug build - as soon as I do a developer build, I don't want
the compiler to optimize any code, anywhere, unless explicitly told so.
As code is traditionally known to occasionally behave differently for
different -O levels, I'm fine with my personal builds by default using
the same -O2 as production builds.
That's probably because you have something really fast to build LO on?
Building with -O2 usually makes the build several times slower than without.
It should be a huge difference for people who hack on whatever they have as
their home machine.
Given that those differences you mention should be either irrelevant in
practice or compiler bugs, even I, having rather fast build system, do not
see -O2 worth using.
Re "unless explicitly told so"---how is one supposed to tell the build
system?
I'm not the build expert here :). You can pass -O2 explicitly to CXXFLAGS, at
least. It's rather a corner case to build with --enable-debug and -O2 at the
same time.
(Or am I confusing what you want to say, and the part of your paragraph
starting "as soon as" shall only apply in the context of explicit
--enable-debug=-sc/? Likely.)
The part starting with "as soon as" is a standalone thought. If somebody does
a developer build, there are not many good reasons why -O2 should be used -
it takes noticably more time and it makes debugging miserable. I can't think
of anything else than final builds and profiling as a good non-corner-case
reason for -O2.
--
Lubos Lunak
l.lunak@suse.cz
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