On Oct 7, 2009, at 7:54 AM, Vincent Labrecque wrote:
>
> And as I'm writing this, with regards to optimization flags, maybe
> the sage build system should provide an abstraction over -On. As
> I'm sure you know, these have widely differing behaviors across
> compilers. Sometimes -O3 will do nothing, sometimes it will break
> your code. ``high'', ``medium'' and ``low'' can be translated by an
> expert on the particular platform (os/compiler/compiler-version).
This probably should even be per-package. In particular with packages
doing complex operation chains. It could be made easy for a package
to change the optimization level.
To put what I tried to explain in the last post in practice, here's
over egineering in the form of a helper program, where packages can
downgrade optimization levels if they know better:
eval `./interpret-optimization -O0 -O2 -O3`
#runs CFLAGS_OPTIMIZATION_LOW=-O0; export CFLAGS_OPTIMIZATION_LOW
# CFLAGS_OPTIMIZATION_MEDIUM=-O2; export
CFLAGS_OPTIMIZATION_MEDIUM
# CFLAGS_OPTIMIZATION_HIGH=-O3; export
CFLAGS_OPTIMIZATION_MEDIUM
# Here's what could happen if another part of the build system
decided that anything over -O3 was unsafe.
CFLAGS_OPTIMIZATION_HIGH=-O2
eval `./interpret-optimization -O1 -O2 -O4`
# runs CFLAGS_OPTIMIZATION_LOW=-O1; export CFLAGS_OPTIMIZATION_LOW
# CFLAGS_OPTIMIZATION_MEDIUM=-O2; export
CFLAGS_OPTIMIZATION_MEDIUM
Maybe one would want to also make sure low <= medium <= high at all
times, which would require a few more lines.
Keep in mind that this was only barely tested. Anyway. Here's how
you can unintrusively share environment variables.
--Vincent
#!/bin/sh
new_low=${1-"-O0"}; new_medium=${2-"-O2"}; new_high=${3-"-O3"}
current_low=${CFLAGS_OPTIMIZATION_LOW-"-O10"}
current_medium=${CFLAGS_OPTIMIZATION_MEDIUM-"-O10"}
current_high=${CFLAGS_OPTIMIZATION_HIGH-"-O10"}
new_low_n=`echo $new_low | sed 's/^-O//'`
new_medium_n=`echo $new_medium | sed 's/^-O//'`
new_high_n=`echo $new_high | sed 's/^-O//'`
current_low_n=`echo $current_low | sed 's/^-O//'`;
current_medium_n=`echo $current_medium | sed 's/^-O//'`
current_high_n=`echo $current_high | sed 's/-O//'`
[ "$current_low_n" -gt "$new_low_n" ] && echo
'CFLAGS_OPTIMIZATION_LOW='"$new_low"'; export CFLAGS_OPTIMIZATION_LOW'
[ "$current_medium_n" -gt "$new_medium_n" ] && echo
'CFLAGS_OPTIMIZATION_MEDIUM='"$new_medium"'; export
CFLAGS_OPTIMIZATION_MEDIUM'
[ "$current_high_n" -gt "$new_high_n" ] && echo
'CFLAGS_OPTIMIZATION_HIGH='"$new_high"'; export
CFLAGS_OPTIMIZATION_HIGH'
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