Re: Setting optimizations without violating autotools principles

[Ralf Wildenhues]

Hi Chris,

On Thu, Jul 07, 2011 at 01:36:29PM -0700, Chris Stankevitz wrote:
> Q1: How do I specify that I want optimizations turned off?
> a) in Makefile.am: AM_CFLAGS = -O0

That won't work as user CFLAGS come after AM_CFLAGS in the command line.

> b) in configure.ac: CFLAGS="$CFLAGS -O0"
> c) other
> 
> Q2: Does your answer for Q1 work even when I use AC_PROG_CC which places -02 
> in CFLAGS?
> 
> Q3: Does your answer for Q1 violate this autotools principle:
> You should never redefine a user variable such as CFLAGS 
> (http://tinyurl.com/3wkfdp5)
> 
> Q4: Does AC_PROG_CC violate this principle?

AC_PROG_CC is documented to enable optimization, and enable
debugging if feasible[1], iff the user hasn't set her own
preferences.

You can do so too:

# Override CFLAGS if not set by the user.
test ${CFLAGS+set} = set || CFLAGS=-O0
AC_PROG_CC

which answers Q1b and Q2.  Answer to Q3: no.  :-)

Hope that helps.

If you want to munge with CFLAGS but also want to take into account
what AC_PROG_CC would have set, you can do things like

if test ${CFLAGS+set} = set; then
  CFLAGS_set_by_user=true
else
  CFLAGS_set_by_user=false
fi
AC_PROG_CC
# Now, do your overriding based on $CFLAGS and $CFLAGS_set_by_user
# and whatever other data.

Cheers,
Ralf

[1] Yes, its definition of "feasible" was maaaybee somewhat valid ten
years, ago, but it definitely isn't today, and I don't know whether
it actually was back then.  Me no Autoconfer back then.