You can't (as per a comment by Simon Urbanek on r-devel a while back).
But it should not matter as AFAIK the right-most value wins. And R puts its values to the left, and lets you add your values (eg via CXX_FLAGS
from, say, ~/.R/Makevars
or PKG_CXXFLAGS
from the src/Makevars
in your package) to the right.
So just override with -O3
and it should be -O3
.
For what it is worth, my current values in ~/.R/Makevars
are:
CFLAGS += -O3 -Wall -pipe -pedantic -std=gnu99
CXXFLAGS += -O3 -Wall -pipe -Wno-unused -pedantic
and you could of course throw in -mnative
or your specific CPU identifier.
Lastly, if you really wanted you could edit /etc/R/Makeconf
but you'd have to do that
after each upgrade of the R package. And as I argue here you do not need to as the scheme suggested here should work.
Edit: In response to your edit:
a) The clear recommendation on r-devel (please check the archives) is that you should avoid Makefile logic if you can. IIRC this echoed in the Writing R Extension manual.
b) You declared a rule to build an .o
(object) file from an .f
(source) file. Did you try doing the same with cpp instead of f?
Lastly, you have not explained exactly why the world is coming to an end if your file is built with -O2 rather than -O3. You should understand that as an author of source, you can't fully control with which compiler options (let alone compiler versions) people will build your package.