Re: RFC: #pragma optimization_level

[Marcin Dalecki <martin at dalecki dot de>]

On 2005-04-05, at 16:12, Nix wrote:
> > I could turn the question back: What's so hard about grepping the 
> > source?
>
> Because one does not expect to find compilation flags embedded in the
> source?

One does - if not grown up in the limited gcc "community". All the high 
scale
compilers out there DO IT.

>  Because generated source is fairly common?

No it isn't.

>  Because eventually
> that runs you into `what's so hard about predicting the behaviour of
> this code generator in order to...' and then you ram straight into
> the halting problem, or, worse, Qt's qmake program. :)
>
> (None of these are strong arguments, I'll admit, but if your argument
> *for* is `it's convenient', then an argument *against* of `it's
> unexpected' is stronger than it looks.

... Lot's of perfectly valid descriptions of by autoconf/automake are a 
horror from
software maintenance point of view deleted... Please look around the 
corner
away from the JBLD (Joes Bloated Linux Distro). It doesn't have to be 
all
the difficult to just control the compilation process ...


> Actually, glibc is a good argument *against* the need for this feature:
> it has a large number of places where unusual one-off CFLAGS are
> required, and it manages to do them all via one-file overrides in the
> makefiles. See e.g. linuxthreads/sysdeps/i386/Makefile for an extensive
> use of this. csu/Makefile has an example of *completely* overriding the
> CFLAGS for a single file that is especially delicate (initfini.s).

Please reread what you describe: You describe a packages, which needs a 
genuine
way to fine control the compilation options. I think it can't be 
questioned that
a sufficiently low level of system programming there is such a need.
Another striking example is the need of the Linux kernel to disable the 
frame pointer
firmly in the schedule() function to maintain the stack layout for a 
context switch.
You see: The requirement is for a single function and not a file.
Some goes for glibc where what you describe is less then esthetically 
neutral.

Since those packages don't have any other choice they resort to ugly 
manipulating of
very very fragile thing: environment variables.

Look there *are* good reasons why so many high grade professional 
compilers do it.
It's not something pretty. But the alternatives are just plain ugly 
(glibc/kernel).