使用编译器注释可检查自动作用域结果,并确定是否因自动作用域失败而对并行区域进行了序列化。
使用 -g 调试选项编译时,编译器将生成行内注释。可以使用 er_src 命令查看这个生成的注释,如下所示。(er_src 命令作为 Solaris Studio 软件的一部分提供;有关更多信息,请参见 er_src(1) 手册页或《Solaris Studio 性能分析器》手册)。
使用 -xvpara 选项进行编译是一个良好的开端。使用 -xvpara 进行编译可大体确定针对特定构造的自动作用域是否成功。以下是一个示例:
示例 6-1 使用 -vpara 自动确定作用域
%cat source1.f INTEGER X(100), Y(100), I, T C$OMP PARALLEL DO DEFAULT(__AUTO) DO I=1, 100 T = Y(I) X(I) = T*T END DO C$OMP END PARALLEL DO END %f95 -xopenmp -xO3 -vpara -c -g source1.f "source1.f", line 2: Autoscoping for OpenMP construct succeeded. Check er_src for details
如果针对特定构造的自动作用域失败,将发出本示例中所示的警告消息(使用 -xvpara):
示例 6-2 使用 -vpara 自动确定作用域失败
%cat source2.f INTEGER X(100), Y(100), I, T C$OMP PARALLEL DO DEFAULT(__AUTO) DO I=1, 100 T = Y(I) CALL FOO(X) X(I) = T*T END DO C$OMP END PARALLEL DO END %f95 -xopenmp -xO3 -vpara -c -g source2.f "source2.f", line 2: Warning: Autoscoping for OpenMP construct failed. Check er-src for details. Parallel region will be executed by a single thread.
er_src 所显示的编译器注释中显示了更详细的信息:
% er_src source2.o Source file: source2.f Object file: source2.o Load Object: source2.o 1. INTEGER X(100), Y(100), I, T Source OpenMP region below has tag R1 Variables autoscoped as SHARED in R1: y Variables autoscoped as PRIVATE in R1: t, i Variables treated as shared because they cannot be autoscoped in R1: x R1 will be executed by a single thread because autoscoping for some variable s was not successful Private variables in R1: i, t Shared variables in R1: y, x 2. C$OMP PARALLEL DO DEFAULT(__AUTO) Source loop below has tag L1 L1 parallelized by explicit user directive L1 autoparallelized L1 parallel loop-body code placed in function _$d1A2.MAIN_ along with 0 inne r loops L1 could not be pipelined because it contains calls 3. DO I=1, 100 4. T = Y(I) 5. CALL FOO(X) 6. X(I) = T*T 7. END DO 8. C$OMP END PARALLEL DO 9. END 10.