Re: flag issue in AC_PROG_CXX for Sun Studio

[Bob Friesenhahn]

On Fri, 26 Feb 2010, Ralf Wildenhues wrote:
> > Thankfully, CFLAGS and CXXFLAGS are separate variables.  So it sounds like
> > all we have to do is teach AC_PROG_CXX to decide if this is the Sun C++
> > compiler, and if so, use -g0 instead of -g. But I don't have quick access
> > to the Sun compiler, to write a reliable test for deciding between the two
> > ideas, so I'm relying on some help on that front.
>
> I agree that also disabling inlining may be weird, and that the default
> choices for CFLAGS and CXXFLAGS may make questionable assumptions about
> bug distribution in (esp. past) compilers, but is it worth changing this
> long-known semantics for that?
>
> More, is it worth deviating from feature tests for this setting?  Other
> compilers accept -g0 too, for example GCC does and it doesn't do what
> we would like to have.

The decision to pass -g as a default is strongly influenced by GCC's 
almost unique ability to achieve full optimization with debugging 
enabled.  While Sun Studio will accept -g or -g0 (and provide a level 
of debugging), either of these may have a negative influence on 
optimizations.  In my opinion, it does not make sense for debugging to 
be applied to most non-GCC compilers as a default since the resulting 
code may run slower and the default should provide well optimized 
code.

There are other issues with Sun Studio as well.  When I want to 
profile GraphicsMagick I use CFLAGS '-g -xO3' because an optimization 
level of less than -xO3 disables OpenMP support, and the profiler 
needs -g in order to provide human readable output.  Optimization 
levels greater than -xO3 don't provide the profiler with the data it 
needs.

Bob
--
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/