[Rcpp-devel] Optimization flag may be needed in Makevars.win for 4.9.2 toolchain

[Avraham Adler]

I've been testing a GCC 4.9.2-based toolchain for Windows for the last
week or so, and today fell afoul of the error uncovered here
<https://stat.ethz.ch/pipermail/r-devel/2015-March/070814.html>. I've
been passing different optimization flags, and Rcpp compiled properly
under every one EXCEPT when a -march (ivybridge) flag was passed
without an optimization flag. In that case, I received the
"collect2.exe: error: ld returned 5 exit status" error as discussed on
R-devel. Passing a -mtune flag without an -O flag did not cause an
error.

Downloading the Rcpp source code and manually adding -O2 to Rcpp's
Makevars.win, re-tar/gzipping it and installing the local version
allowed Rcpp to compile properly.

I don't know if it is better to tell people to change their local
Makevars under HOME/.R to pass -O2 or -O3 (that would probably be a
call by you, Dirk, as you would know best if O3 would help or hinder),
or if it is better to have Rcpp enforce it, but it should be noted
somewhere once a 4.9.2-based Windows is eventually released.

Thank you,

Avi