From: Kasper Daniel Hansen <>
Date: Tue 20 Mar 2007 - 21:32:08 GMT

On Mar 20, 2007, at 7:58 PM, Ernest Turro wrote:

> Why is it that R places CFLAGS after PKG_CFLAGS and not before when
> compiling a package (e.g. through R CMD build pkg)? This can be
> problematic if, for instance, you want to use -O3, but -O2 is in
> R_HOME/etc/Makeconf. If -O2 (in CFLAGS) appears after -O3 (in
> PKG_CFLAGS), you are left with what you didn't want: -O2.
> In R-exts, it says that "Flags which are set in file etc/Makeconf can
> be overridden by the environment variable MAKEFLAGS (at least for
> systems using GNU make), as in (Bourne shell syntax)" but this
> doesn't work if I set either MAKEFLAGS or CFLAGS/CXXFLAGS in my
> script or package Makevars.

In you example above you want to force the user to use a higher optimization flag. But (s)he may have very valid reasons for not doing so - and are you really sure that you are comfortable setting - O3 on _all_ platforms? Also -O. is GCC specific so it does not work for all compilers.

If a user really wants a super fast R (s)he will (should) compile it with -O3.

Having said that, I think it is problematic that one cannot _downgrade_ the optimization. I am maintaining a package including an external library (outside of my control) which does not work with -O2 on some platforms, due to alignment problems.

> Does anyone have any ideas on how to reliably override the default
> CFLAGS/CXXFLAGS given in Makeconf?

I was given the following code some while ago by Simon Urbanek:

all: $(SHLIB)

MYCXXFLAGS=-O0 %.o: %.cpp

         $(CXX) $(ALL_CPPFLAGS) $(ALL_CXXFLAGS) $(MYCXXFLAGS) -c $< - o $@

(this is for C++, I imagine the syntax is straightforward for C). Put it in src/Makevars.

But as I said above, I think it is a bad idea to raise the optimization level for all users.


> Many thanks,
> Ernest
> ______________________________________________
> mailing list
> mailing list Received on Wed Mar 21 08:34:56 2007

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