R devel - May 2006 - suppressing "global" cppflags in an individual package

Hi

I can use PKG_CPPFLAGS in a Makevars file to add additional flags to  
the c++ compiler for a given package. Is it possible to remove flags  
passed to the packages from R. Eg: say R have been compiled with -O2  
and I want the package to be compiled with another optimization level?

/Kasper

Kasper Daniel Hansen wrote:
> Hi
> 
> I can use PKG_CPPFLAGS in a Makevars file to add additional flags to  
> the c++ compiler for a given package. Is it possible to remove flags  
> passed to the packages from R. Eg: say R have been compiled with -O2  
> and I want the package to be compiled with another optimization level?
Do you mean the flags passed to the c++ compiler (CXXFLAGS) or
to the C proprocessor (CPPFLAGS)? Do not confuse the two.

I think the "proper" way would be to write a full makefile.
(there are plenty of examples on CRAN).

Now, out of curiosity - why would you want to do that? The actual 
difference in CPU time usage is often small (10%?), so unless the
package triggers a compiler bug at specific optimization level and
gets mis-compiled, it is probably not worth the trouble. And if
the package is that sensitive to optimization level and can get 
mis-compiled, one of them (the package or the compiler) needs fixing.

HTL

On May 9, 2006, at 9:49 AM, Hin-Tak Leung wrote:
> Kasper Daniel Hansen wrote:
>> Hi
>> I can use PKG_CPPFLAGS in a Makevars file to add additional flags  
>> to  the c++ compiler for a given package. Is it possible to remove  
>> flags  passed to the packages from R. Eg: say R have been compiled  
>> with -O2  and I want the package to be compiled with another  
>> optimization level?
>
> Do you mean the flags passed to the c++ compiler (CXXFLAGS) or
> to the C proprocessor (CPPFLAGS)? Do not confuse the two.
Hmm good point. I think I have indeed confused the two.
> I think the "proper" way would be to write a full makefile.
> (there are plenty of examples on CRAN).
I would like to avoid this, see below.
> Now, out of curiosity - why would you want to do that? The actual  
> difference in CPU time usage is often small (10%?), so unless the
> package triggers a compiler bug at specific optimization level and
> gets mis-compiled, it is probably not worth the trouble. And if
> the package is that sensitive to optimization level and can get mis- 
> compiled, one of them (the package or the compiler) needs fixing.
It is indeed the case that after updating to GCC 4 the package gets  
broken using -O2. I agree this needs to be fixed, but the error  
(which I believe I have kind of localized, but not really understood)  
stems from a C++ library we have little control over, so it would be  
nice to have a fix for the time being that does not require a  
reinstallation of R - especially since we actually have users who  
currently (or soon will be) testing it. I was thus looking for a  
temporary quick fix allowing me to disable the optimization level,  
while I take the time to fix it properly.

Kurt Hornik have replied of-list that it is possible to do so using a  
~/.R/Makevars file (which I have not had the time to test  
unfortunately), but reading your comment about CPPFLAGS and CXXFLAGS  
makes me think I can indeed override it using the package Makevars  
file. The flags I was passing to the compiler were library locations  
anyway which was for the preprocessor.

Thanks for the help, Kasper

> HTL