[Rd] problem customizing CXXFLAGS in Windows
Prof Brian Ripley
ripley at stats.ox.ac.uk
Fri Apr 18 19:41:36 CEST 2008
On Fri, 18 Apr 2008, Ian Fiske wrote:
> Hi all,
> I am running R 2.6.2 in Windows XP with Rtools 2.7 and am trying to compile
> a shared library in Windows with customized level of optimization.
> Specifically, I would like to have "-O3 -funroll-loops" as flags when I run
> "R CMD SHLIB ***.cc" to speed the program for my simulations.
> I have read through the documentation and have tried adding the line
> PKG_CXXFLAGS = -O3 -funroll-loops
> in my Makevars in my package's src directory. However, this places the
> flags before the -O2 flag, thereby overriding it.
I presume you meant the opposite -- 'it' refers to its immediate
antecdent, 'the -O2 flag', which overrides not is overridden? That is,
the flags are processed from left to right and later settings win.
> I have also tried creating a config.site file in R_HOME/etc, but that
> seems to be ignored.
What gave you the idea that would be relevant? I don't see it in any of
> I found a possible solution at
> http://tolstoy.newcastle.edu.au/R/e2/devel/07/03/2520.html. However, when I
> use this suggestion, I get errors that R.h cannot be found.
> Please note that I do not plan to submit this package to CRAN or to other
> users with the modified flags, but I just need to set them on my machine to
> speed up simulations for testing, etc.
>From the R-admin manual:
'Package-specific compilation flags can be overridden or added to using
the personal file $HOME/.R/Makevars.win, or if that does not exist,
$HOME/.R/Makevars. (See the rw-FAQ for the meaning of $HOME.) For the
record, the order of precedence is (last wins)
* MakeDll and MkRules
* src/Makevars.win if it exists, otherwise src/Makevars
* $HOME/.R/Makevars.win if it exists, otherwise $HOME/.R/Makevars.
* src/Makefile.win if present causes all but the last of the above to
So you can set CXXFLAGS in src/Makevars.win and that will override the
system's values. Or you could change the system setting to -O3 in
MakeDll -- it is -O3 for C and Fortran, but -O2 for C++ (which R itself
does not use) because -O3 for C++ used to be problematic (with gcc 3.4.5,
not the current version).
I think the URL you give is too old -- it probably preceeds the corrected
separation of CPPFLAGS and C[XX]FLAGS. The rule is (from MkRules)
$(CXX) $(CPPFLAGS) $($*-CPPFLAGS) $(CXXFLAGS) $($*-CXXFLAGS) -c $<
and so CPPFLAGS should contain include paths, and CXXFLAGS optimization
I've just taken a C++-using package and added
to its Makevars. All the headers were found, and that was the
optimization level used.
> I appreciate any suggestions,
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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