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I have some strange troubles with Rcpp - it uses unpredictable C++ compiler. This question is somewhat similar to this question.
I'm on OSX, I have 2 complilers - default clang and clang-omp with openmp support. Also I have following ~/.R/Makevars file (where I set up clang-omp as default compiler):

CC=clang-omp
CXX=clang-omp++
CFLAGS += -O3 -Wall -pipe -pedantic -std=gnu99
CXXFLAGS += -O3 -Wall -pipe -Wno-unused -pedantic -fopenmp

The problem is that, the package I'm developing compiles with clang++, not clang-omp++. I also tried (as experiment to lacate issue) to change package src/Makevars and set CXX=clang-omp++ and moreover modified $R_HOME/etc/Makeconf CXX entry to CXX = clang-omp++. No luck - it still compiles with clang++. Have no idea why it happens.

Also here is small reproducible (both from console R and from Rstudio) example (don't know whether it related to issue above). Suppose 2 very similar cpp functions:
1. 

#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
NumericVector timesTwo(NumericVector x) {
  return x * 2;
}

Call sourceCpp from R:

library(Rcpp)  
sourceCpp("src/Rcpp_compiler.cpp", verbose = T)

/Library/Frameworks/R.framework/Resources/bin/R CMD SHLIB -o 'sourceCpp_1.so' 'Rcpp_compiler.cpp'
clang-omp++ -I/Library/Frameworks/R.framework/Resources/include -DNDEBUG -I/usr/local/include -I/usr/local/include/freetype2 -I/opt/X11/include -I"/Users/dmitryselivanov/Library/R/3.2/library/Rcpp/include" -I"/Users/dmitryselivanov/projects/experiments/src" -fPIC -Wall -mtune=core2 -g -O2 -O3 -Wall -pipe -Wno-unused -pedantic -fopenmp -c Rcpp_compiler.cpp -o Rcpp_compiler.o
clang-omp++ -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/Library/Frameworks/R.framework/Resources/lib -L/usr/local/lib -o sourceCpp_1.so Rcpp_compiler.o -F/Library/Frameworks/R.framework/.. -framework R -Wl,-framework -Wl,CoreFoundation

Work as expected - uses clang-omp++ and all my flags from ~/.R/Makevars

2.

#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::plugins(cpp11)]]
// [[Rcpp::export]]
NumericVector timesTwo(NumericVector x) {
  return x * 2;
}

Library/Frameworks/R.framework/Resources/bin/R CMD SHLIB -o 'sourceCpp_2.so' 'Rcpp_compiler.cpp'
clang++ -std=c++11 -I/Library/Frameworks/R.framework/Resources/include -DNDEBUG -I/usr/local/include -I/usr/local/include/freetype2 -I/opt/X11/include -I"/Users/dmitryselivanov/Library/R/3.2/library/Rcpp/include" -I"/Users/dmitryselivanov/projects/experiments/src" -fPIC -Wall -mtune=core2 -g -O2 -c Rcpp_compiler.cpp -o Rcpp_compiler.o
clang++ -std=c++11 -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/Library/Frameworks/R.framework/Resources/lib -L/usr/local/lib -o sourceCpp_2.so Rcpp_compiler.o -F/Library/Frameworks/R.framework/.. -framework R -Wl,-framework -Wl,CoreFoundation

I only added // [[Rcpp::plugins(cpp11)]] and it compiles with clang++ instead of clang-omp++

Here is my sessionInfo():

R version 3.2.1 (2015-06-18) Platform: x86_64-apple-darwin13.4.0 (64-bit)
Running under: OS X 10.10.5 (Yosemite)
locale: 1 en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8 attached base packages:
1 stats graphics grDevices utils datasets methods base
other attached packages: 1 Rcpp_0.12.1
loaded via a namespace (and not attached): 1 tools_3.2.1

Community
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Dmitriy Selivanov
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2 Answers2

13

Thanks, to @Dirk hint, I finaly got an answer. Hope, this will save a little bit of time for somebody. Following two lines in ~/.R/Makevars solved my problem: 

CXX1X=clang-omp++

See details in this Writing R Extensions section.

Dmitriy Selivanov
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    You will, of course, have no hope on earth of those kind of make flags making it on to CRAN. I have been through trying to use C++11 and OpenMP for a CRAN package, and found that you almost certainly need a 'configure' script. – Jack Wasey Oct 20 '15 at 22:22
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    Don't think, this is an issue. We can just add `C++11` to `SystemRequirements` and check omp support with `#ifdef _OPENMP ` macro. If it not supported - go with single thread. Anyway, yesterday, I rewrote all my concurrent parts with `RcppParallel` which is far more robust and far more portable - works even on Windows. – Dmitriy Selivanov Oct 21 '15 at 08:41
  • What is CXX1X ? The `Writing R Extensions` refers to CXX11 as a make variable directive to use C++11 compiler for the package. I'm looking for documentation that explains what CXX1X is but can only find info about CXX11, CXX14, CXX17. – Davos Sep 28 '17 at 01:33
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    This was changed since R 3.4. was CXX1X before. – Dmitriy Selivanov Sep 28 '17 at 03:32
-3

I only read one line of your question and stopped there:

I have some strange troubles with Rcpp - it uses unpredictable C++ compiler

That is both wrong and also inflammatory. Please read the R documentation included with your version of R and learn how R sets these things.

Rcpp does nothing extra. All this is default R behaviour:

  • As a user you can set this in ~/.R/Makevars

  • As a package author aiming for portable and CRAN-compatible packages you cannot but have to use, say, configure at package built-time.

This is all documented and has been discussed before.

Dirk Eddelbuettel
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    As usual not very friendly response, but after digging another half of the day, I get solution. Will Accept your answer with my minor modifications which actually resolves my problem. – Dmitriy Selivanov Oct 19 '15 at 19:56
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    You could just come to rcpp-devel (or for this even r-package-devel as you have _packaging_ rather than Rcpp questions) and ask there. – Dirk Eddelbuettel Oct 19 '15 at 20:00
  • If you now have an answer, feel free to add it or edit your question. Good to see that why recommendation of checking "Writing R Extensions" was fruitful for you. – Dirk Eddelbuettel Oct 19 '15 at 20:04
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    Is mailing list right place for such type of questions? Why not SO? – Dmitriy Selivanov Oct 19 '15 at 20:12