> > >> DMC = Digital Mars Compiler? Does Mingw/GDC uses that? I think that > both, g++ and GDC compiled binaries, use the mingw runtime, but I'm not > sure also.
you right, only dmd uses dmc environment, gdc uses mingw's. > > And I don't think it is I/O bound. It is only around 10MB/s, whereas my HD > can do ~100MB/s. Furthermore, on files more compressible, where the speed > was higher, the difference between D and C++ was higher too. And if is in > fact I/O bound, then D is MORE than 50% slower than C++. to minimize system load and I/O impact, run the same file in the loop, like 5-10 times, it will be located in kernel cache. > > The difference is likely because of differences in external C libraries. >> > Both, the D and C++ versions, use C's stdio library. What is the > difference? > > probably because gdc backend make worse job on optimizing D AST vs C++ AST. I've got following results: C:\D>echo off FF=a.doc C++ compress a.doc a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.36 s. a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.36 s. a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.33 s. a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.34 s. a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.34 s. "C++ decompress" a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.50 s. a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.51 s. a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.51 s. a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.50 s. a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.50 s. "D compress" a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.11 s. a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.08 s. a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.08 s. "D decompress" a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.17 s. a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.19 s. a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.19 s. a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.22 s. a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.25 s. "Done" So, what's up? I'm used the same backend too, but DMC (-o -6) vs DMD (-release -inline -O -noboundscheck). I don't know DMC optimization flags, so probably results might be better for it. Lets try to compile by MS CL (-Ox) C:\D>echo off FF=a.doc C++ compress a.doc a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.03 s. a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.02 s. a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.04 s. a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.03 s. a.doc (2694428 bytes) -> a.doc.cmp (1459227 bytes) in 1.01 s. "C++ decompress" a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.08 s. a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.06 s. a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.07 s. a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.07 s. a.doc.cmp (1459227 bytes) -> a.doc.cmp.or (2694428 bytes) in 1.07 s. "D compress" a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.08 s. a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.09 s. a.doc (2694428 bytes) -> a.doc.dmp (1459227 bytes) in 1.09 s. "D decompress" a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.15 s. a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.17 s. a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.19 s. a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.17 s. a.doc.dmp (1459227 bytes) -> a.doc.dmp.or (2694428 bytes) in 1.17 s. "Done" Much better for C++, but D is not so worse and about 1.1*C++ too. What we see - different compiler, different story. We should not compare languages for performance but compilers! So many differencies in compilers and environment and definetelly C++ is much more mature for performance now but also D has own benefits (faster development/debugging and more reliable code). Thanks, Oleg. PS. BTW, this code still can be optimized quite a lot.
