使用rcpp :: cppFunction编译许多嵌套循环

Question

R用户

我正在尝试解决组合问题蛮力以评估近似计算的质量。 为此，我编写了一个小的R函数，该函数为变量r输出了一个非常丑陋的rcpp函数，其中包含r个嵌套循环以及一些中断条件。 但是，当r开始在20+范围内时，用rcpp :: cppFunction编译函数将花费很长时间。 ..

有什么解释为什么rcpp编译会因为大量的嵌套循环而中断？ 当我使用g ++将函数编译为普通的C ++程序时，它将在不到一秒钟的时间内立即编译完成，并且运行起来也完美无缺（使用cout代替Rcout）。

我可能缺少明显的东西，因为当我除去除最里面的中断条件以外的所有条件时，它可以使用rcpp进行漂亮地编译。 但是，当我也删除了最后一个中断条件时，它不会再次完成编译...有什么建议吗？

PS这是r = 20的示例程序，我仍在等待完成编译。 警告：这很丑陋，但会自动生成。

cppFunction('
int make_tList_rcpp() {
int r = 20;
std::cout << std::endl;
 for (int t20=0; t20 <= floor(r/20); t20++) {
  for (int t19=0; t19 <= floor(r/19); t19++) {
   for (int t18=0; t18 <= floor(r/18); t18++) {
    for (int t17=0; t17 <= floor(r/17); t17++) {
     for (int t16=0; t16 <= floor(r/16); t16++) {
      for (int t15=0; t15 <= floor(r/15); t15++) {
       for (int t14=0; t14 <= floor(r/14); t14++) {
        for (int t13=0; t13 <= floor(r/13); t13++) {
         for (int t12=0; t12 <= floor(r/12); t12++) {
          for (int t11=0; t11 <= floor(r/11); t11++) {
           for (int t10=0; t10 <= floor(r/10); t10++) {
            for (int t9=0; t9 <= floor(r/9); t9++) {
             for (int t8=0; t8 <= floor(r/8); t8++) {
              for (int t7=0; t7 <= floor(r/7); t7++) {
               for (int t6=0; t6 <= floor(r/6); t6++) {
                for (int t5=0; t5 <= floor(r/5); t5++) {
                 for (int t4=0; t4 <= floor(r/4); t4++) {
                  for (int t3=0; t3 <= floor(r/3); t3++) {
                   for (int t2=0; t2 <= floor(r/2); t2++) {
                    for (int t1=0; t1 <= floor(r/1); t1++) {
                     if ((1*t1+2*t2+3*t3+4*t4+5*t5+6*t6+7*t7+8*t8+9*t9+10*t10+11*t11+12*t12+13*t13+14*t14+15*t15+16*t16+17*t17+18*t18+19*t19+20*t20) == r) {
                      Rcout << t1 << "," << t2 << "," << t3 << "," << t4 << "," << t5 << "," << t6 << "," << t7 << "," << t8 << "," << t9 << "," << t10 << "," << t11 << "," << t12 << "," << t13 << "," << t14 << "," << t15 << "," << t16 << "," << t17 << "," << t18 << "," << t19 << "," << t20 << std::endl;
                     }
                     if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5+4*t4+3*t3+2*t2+1*t1) > r) {
                      break;
                     }
                    }
                    if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5+4*t4+3*t3+2*t2) > r) {
                     break;
                    }
                   }
                   if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5+4*t4+3*t3) > r) {
                    break;
                   }
                  }
                  if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5+4*t4) > r) {
                   break;
                  }
                 }
                 if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5) > r) {
                  break;
                 }
                }
                if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6) > r) {
                 break;
                }
               }
               if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7) > r) {
                break;
               }
              }
              if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8) > r) {
               break;
              }
             }
             if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9) > r) {
              break;
             }
            }
            if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10) > r) {
             break;
            }
           }
           if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11) > r) {
            break;
           }
          }
          if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12) > r) {
           break;
          }
         }
         if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13) > r) {
          break;
         }
        }
        if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14) > r) {
         break;
        }
       }
       if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15) > r) {
        break;
       }
      }
      if ((20*t20+19*t19+18*t18+17*t17+16*t16) > r) {
       break;
      }
     }
     if ((20*t20+19*t19+18*t18+17*t17) > r) {
      break;
     }
    }
    if ((20*t20+19*t19+18*t18) > r) {
     break;
    }
   }
   if ((20*t20+19*t19) > r) {
    break;
   }
  }
  if ((20*t20) > r) {
   break;
  }
 }
 return(0);
}')

正如@spacedman所建议的，这里是使用sourceCpp时的更多调试信息。 正如对sourceCpp建议的进一步评论所写，它似乎可以在Linux上运行，因此可能是与Mac相关的问题...：

> sourceCpp(file="foobar.cpp",verbose=TRUE, rebuild=TRUE)

Generated extern "C" functions 
--------------------------------------------------------


#include <Rcpp.h>
// make_tList_rcpp
void make_tList_rcpp();
RcppExport SEXP sourceCpp_1_make_tList_rcpp() {
BEGIN_RCPP
    Rcpp::RNGScope rcpp_rngScope_gen;
    make_tList_rcpp();
    return R_NilValue;
END_RCPP
}

Generated R functions 
-------------------------------------------------------

`.sourceCpp_1_DLLInfo` <- dyn.load('/private/var/folders/bj/k_b2brs5443bmm8699v5fvxw0000gn/T/RtmpDSa3m8/sourceCpp-x86_64-apple-darwin13.4.0-0.12.9/sourcecpp_a7c1e15e92a/sourceCpp_8.so')

make_tList_rcpp <- Rcpp:::sourceCppFunction(function() {}, TRUE, `.sourceCpp_1_DLLInfo`, 'sourceCpp_1_make_tList_rcpp')

rm(`.sourceCpp_1_DLLInfo`)

Building shared library
--------------------------------------------------------

DIR: /private/var/folders/bj/k_b2brs5443bmm8699v5fvxw0000gn/T/RtmpDSa3m8/sourceCpp-x86_64-apple-darwin13.4.0-0.12.9/sourcecpp_a7c1e15e92a

/Library/Frameworks/R.framework/Resources/bin/R CMD SHLIB -o 'sourceCpp_8.so' --preclean  'foobar.cpp'  
clang++ -I/Library/Frameworks/R.framework/Resources/include -DNDEBUG  -I/usr/local/include -I/usr/local/include/freetype2 -I/opt/X11/include  -I"/Users/hoehle/Library/R/3.3/library/Rcpp/include" -I"/Users/hoehle/Sandbox/Blog/_source"   -fPIC  -Wall -mtune=core2 -g -O2  -c foobar.cpp -o foobar.o

（这是它的悬挂位置...）

PS，这是sessionInfo（）

R version 3.3.2 (2016-10-31)
Platform: x86_64-apple-darwin13.4.0 (64-bit)
Running under: macOS Sierra 10.12.2

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_0.12.9

loaded via a namespace (and not attached):
[1] compiler_3.3.2 tools_3.3.2   

Answer 1

它可以编译并在除 macOS之外的所有平台上运行。

编辑后，我们将获得一些有用的调试信息。 特别是，使用的标志：

clang++ -I/Library/Frameworks/R.framework/Resources/include -DNDEBUG  -I/usr/local/include -I/usr/local/include/freetype2 -I/opt/X11/include  -I"/Users/hoehle/Library/R/3.3/library/Rcpp/include" -I"/Users/hoehle/Sandbox/Blog/_source"   -fPIC  -Wall -mtune=core2 -g -O2  -c foobar.cpp -o foobar.o

在macOS上嵌套for循环编译存在问题的原因与clang如何优化-O2 vs -Os下的嵌套循环有关。 具体地，存在洼回归大约clang直接影响，以优化的能力v3.0中所述环。 特别是，请参阅：

https://llvm.org/bugs/show_bug.cgi?id=16196

该问题似乎已在3.8中修复。 缺点是您必须手动更新到此编译器，因为此回归在所有macOS机器上都随clang版本一起提供。 您可能只想在macOS上切换到gcc 。 无论如何，以下文章应有助于通过自制程序和~/.R/Makevars设置适当的编译器

http://thecoatlessprofessor.com/programming/openmp-in-r-on-os-x/

您可能希望使用sourceCpp()而不是cppFunction()因为后者意味着更简单的功能。 sourceCpp()函数适用于更复杂的情况。 另外，我可能会选择避免指定int返回类型。

使用sourceCpp()示例

# In R
sourceCpp("path_to/example_comb.cpp")

文件： example_comb.cpp

#include <Rcpp.h>

// [[Rcpp::export]]
void make_tList_rcpp() {
    int r = 20;
    std::cout << std::endl;
    for (int t20=0; t20 <= floor(r/20); t20++) {
        for (int t19=0; t19 <= floor(r/19); t19++) {
            for (int t18=0; t18 <= floor(r/18); t18++) {
                for (int t17=0; t17 <= floor(r/17); t17++) {
                    for (int t16=0; t16 <= floor(r/16); t16++) {
                        for (int t15=0; t15 <= floor(r/15); t15++) {
                            for (int t14=0; t14 <= floor(r/14); t14++) {
                                for (int t13=0; t13 <= floor(r/13); t13++) {
                                    for (int t12=0; t12 <= floor(r/12); t12++) {
                                        for (int t11=0; t11 <= floor(r/11); t11++) {
                                            for (int t10=0; t10 <= floor(r/10); t10++) {
                                                for (int t9=0; t9 <= floor(r/9); t9++) {
                                                    for (int t8=0; t8 <= floor(r/8); t8++) {
                                                        for (int t7=0; t7 <= floor(r/7); t7++) {
                                                            for (int t6=0; t6 <= floor(r/6); t6++) {
                                                                for (int t5=0; t5 <= floor(r/5); t5++) {
                                                                    for (int t4=0; t4 <= floor(r/4); t4++) {
                                                                        for (int t3=0; t3 <= floor(r/3); t3++) {
                                                                            for (int t2=0; t2 <= floor(r/2); t2++) {
                                                                                for (int t1=0; t1 <= floor(r/1); t1++) {
                                                                                    if ((1*t1+2*t2+3*t3+4*t4+5*t5+6*t6+7*t7+8*t8+9*t9+10*t10+11*t11+12*t12+13*t13+14*t14+15*t15+16*t16+17*t17+18*t18+19*t19+20*t20) == r) {
                                                                                        Rcpp::Rcout << t1 << "," << t2 << "," << t3 << "," << t4 << "," << t5 << "," << t6 << "," << t7 << "," << t8 << "," << t9 << "," << t10 << "," << t11 << "," << t12 << "," << t13 << "," << t14 << "," << t15 << "," << t16 << "," << t17 << "," << t18 << "," << t19 << "," << t20 << std::endl;
                                                                                    }
                                                                                    if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5+4*t4+3*t3+2*t2+1*t1) > r) {
                                                                                        break;
                                                                                    }
                                                                                }
                                                                                if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5+4*t4+3*t3+2*t2) > r) {
                                                                                    break;
                                                                                }
                                                                            }
                                                                            if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5+4*t4+3*t3) > r) {
                                                                                break;
                                                                            }
                                                                        }
                                                                        if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5+4*t4) > r) {
                                                                            break;
                                                                        }
                                                                    }
                                                                    if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6+5*t5) > r) {
                                                                        break;
                                                                    }
                                                                }
                                                                if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7+6*t6) > r) {
                                                                    break;
                                                                }
                                                            }
                                                            if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8+7*t7) > r) {
                                                                break;
                                                            }
                                                        }
                                                        if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9+8*t8) > r) {
                                                            break;
                                                        }
                                                    }
                                                    if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10+9*t9) > r) {
                                                        break;
                                                    }
                                                }
                                                if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11+10*t10) > r) {
                                                    break;
                                                }
                                            }
                                            if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12+11*t11) > r) {
                                                break;
                                            }
                                        }
                                        if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13+12*t12) > r) {
                                            break;
                                        }
                                    }
                                    if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14+13*t13) > r) {
                                        break;
                                    }
                                }
                                if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15+14*t14) > r) {
                                    break;
                                }
                            }
                            if ((20*t20+19*t19+18*t18+17*t17+16*t16+15*t15) > r) {
                                break;
                            }
                        }
                        if ((20*t20+19*t19+18*t18+17*t17+16*t16) > r) {
                            break;
                        }
                    }
                    if ((20*t20+19*t19+18*t18+17*t17) > r) {
                        break;
                    }
                }
                if ((20*t20+19*t19+18*t18) > r) {
                    break;
                }
            }
            if ((20*t20+19*t19) > r) {
                break;
            }
        }
        if ((20*t20) > r) {
            break;
        }
    }

}


/*** R
# Runs automatically in R after compile
make_tList_rcpp(42)
*/

功能输出：

https://gist.github.com/coatless/aa51267dcda82b42622fdc8e6e566ab7