[R-SIG-Mac] Debug Rcpp with lldb: variables not available

[inf0phile]

* I made a minimal example in order to be reproduced:

library(Rcpp)
library(RcppArmadillo)
RcppArmadillo.package.skeleton()

which create the package anRpackage.
Setting the working directory in this package, I load it by:

library(devtools)
devtools::load_all()

* Then the basic function rcpparma_hello_world() can be executed:

rcpparma_hello_world()

     [,1] [,2] [,3]
[1,]    7    0    0
[2,]    0    7    0
[3,]    0    0    7

* I want now to debug the code with lldb via the Terminal command R -d lldb in order to check the variable values during the execution via the command frame variable.

R -d lldb
(lldb) breakpoint set --name rcpparma_hello_world()
(lldb) run
> library(devtools)
> devtools::load_all()
> rcpparma_hello_world()

anRpackage.so was compiled with optimization - stepping may behave oddly; variables may not be available.

Indeed, the problem is that most of variables are not available:

> next
> frame variable

(arma::mat) m1 = <no location, value may have been optimized out>
(arma::mat) m2 = <no location, value may have been optimized out>

* I read in the previous link the following recommandations:

    you may consider producing so-called ‘debug’ builds, with optimization toned down, when attempting to debug these kinds of issues as well. For building R packages, this effectively amounts to something like CXXFLAGS=-g -O0 in your ~/.R/Makevars file)

* I have tried it but it seems to have no effect under the compilation flags used since I have a local file Makevars in my package to specify the way of compiling with RcppArdimillo, whose flags are:

CXX_STD = CXX11
PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS)
PKG_LIBS = $(SHLIB_OPENMP_CXXFLAGS) $(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS)

* Then, the command devtools::load_all() produces the line-command compilation given below, in which there is indeed -g -O2 making some code optimization:

clang++ -mmacosx-version-min=10.13 -std=gnu++11 -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG  -I'/Library/Frameworks/R.framework/Versions/4.0/Resources/library/Rcpp/include' -I'/Library/Frameworks/R.framework/Versions/4.0/Resources/library/RcppArmadillo/include' -I/usr/local/include    -fPIC  -Wall -g -O2  -c rcpparma_hello_world.cpp -o rcpparma_hello_world.o

Question: how can I have access to the variables in debugging mode?

Thanks

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
Le jeudi 11 juin 2020 18:48, inf0phile via R-SIG-Mac <r-sig-mac using r-project.org> a écrit :

> Hello,
>
> I'm making a package with Rcpp (and RcppArmadillo) under the latest version of Rstudio (1.3.959) and R (4.0.0).
>
> -   The compilation of the cpp files (with clang) is working well
>
>     clang++ -mmacosx-version-min=10.13 -std=gnu++11 -I"/Library/Frameworks/
>     R.framework/Resources/include
>     " -DNDEBUG -I'/Library/Frameworks/
>     R.framework/Versions/4.0/Resources/library/Rcpp/include
>     ' -I'/Library/Frameworks/
>     R.framework/Versions/4.0/Resources/library/RcppArmadillo/include
>     ' -I/usr/local/include -fPIC -Wall -g -O2 -c compensator_Rcpp.cpp -o compensator_Rcpp.o
>
>     This command is automatically generated by pushing the Rstudio package dev button "Install and restart"
>
> -   I want now to debug the code with lldb (https://kevinushey.github.io/blog/2015/04/13/debugging-with-lldb/) via the Terminal command R -d lldb in order to check the variable values during the execution via the command frame variable. The problem is most of them are not available:
>
>     (SEXP) lambda = <variable not available>
>
>
> (Rcpp::NumericVector) beta = <no location, value may have been optimized out>
> (int) index = <variable not available>
>
> -   I read in the previous link the following recommandations:
>
> > you may consider producing so-called ‘debug’ builds, with optimization toned down, when attempting to debug these kinds of issues as well. For building R packages, this effectively amounts to something like CXXFLAGS=-g -O0 in your ~/.R/Makevars file)
>
> -   I have tried it but it seems to have no effect under the compilation flags used since I have a local file Makevars in my package to specify the way of compiling with RcppArdimillo (http://dirk.eddelbuettel.com/blog/2017/06/04/), whose flags are:
>
>     CXX_STD = CXX11
>     PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS)
>     PKG_LIBS = $(SHLIB_OPENMP_CXXFLAGS) $(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS)
>
>     producing the line-command compilation given above, in which there is indeed -g -O2 making some code optimization.
>
>     Question: how can I have access to the variables in debugging mode?
>
>     Thanks
>     [[alternative HTML version deleted]]
>
>
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