Re: Checking for GCC 4

[Harlan Stenn]

> On Fri, 2006-02-03 at 06:07 +0000, Harlan Stenn wrote:
> > Ralf,
> > 
> > How about something that would use AC_RUN_IFELSE()?
> 
> We are talking about distinguishing different compiler
> versions !!!!!!!!!

No, we are talking about making decisions using, say, the version number
of a tool or the output of config.guess (or something like that).

> Why on earth would you want to run something conditionally, depending on
> which compilers it had been compiled with?

I don't know, but that doesn't mean there isn't a good reason do to it.

> > There's a reason it come with ACTION-IF-CROSS-COMPILING - it means one
> > CANNOT feature test so one has to make the decision beforehand  and
> > decide based on some other factors.
> 
> You are talking about a package using a toolchain to require _target_
> run-time features. Right, these are occasionally required.
> 
> But we are talking about compiler/toolchain features. The cross
> compilers/toolchains *never* retrieve anything from a target at
> run-time.

Perhaps we had a little confusion about exactly what we were talking
about.

I was going off about folks who say "the only way to go is feature test
- never rely on version numbers", as I have had that discussion before
and it included testing based on OS type or version.

In general I prefer to test.  If that's "too difficult" I'll go for
version numbers or the CPU-Vendor-OS string (I have something that
converts the output of config.guess and some optional local poking
around into something I find useful).

> If the toolchains require knowledge about a target's runtime feature,
> the toolchains must know about it in advance, but the
> application/package using the toolchain doesn't have to. It can
> compile/link check the toolchain.

This is simply a degenerate case.  We could certainly go back to the old
days where folks said #ifdef BSD or #ifdef SYSIII.

The point I was trying to make is that "feature testing is good and we
cannot always do it TODAY.  Sometimes we must use another way, like
version numbers."

H