Misc questions:- licensing, VC++ IDE compatible, GPGPU, LTCG, QT, SDL

bearophile bearophileHUGS at lycos.com
Sun May 16 08:00:40 PDT 2010

Dan W.:

> 3: I need my program to be as fast as possible. The Visual C++ compiler has
> features such as "link-time code generation" and "Profile guided optimization".
> Does D have equivalents?

You can't ask a new open source language to have the features of a ten+ years old commercial compiler.
If you compile D1-Tango code on Linux 32 bit using LDC using all the correct compile switches you can get performance comparable to C code compiled with GCC. LDC does not have vectorization (that gcc has) but has link-time optimization that GCC 4.5 has just in part. This is the very best performance you can hope with D.

General note: a trap D has put itself into: a significant group of people seem interested in D only as a high performance language. But history shows that nearly no new language starts its life being very fast. High performance, especially if you mean it as compared to quite mature C++ implementations, is something that can only come some years after a language has already reached some form of success and people start to use weeks, months or years just tuning the GC, creating whole new kinds of GC, inventing and implementing other D-specific optimizations, implementing a good escape analysis, implementing a good devirtualization+inlining of virtual functions, implementing various different kinds of efficient vectorizations, implementing a good pointer alias analysis, and so on.

Today some kind of Java programs running on HotSpot have a performance comparable to C++ programs. JavaScript running on V8 is often less than ten times slower than well compiled C. But for years both Java and JavaScript were dog-slow. Most things in D are designed to require a simple enough compiler, it doesn't need an advanced JIT just to be efficient. So even naively compiled D programs aren't 50 times slower than equivalent C++ programs. Yet, the performance is not the same as commercial C++ compilers, and it will not be like that unless groups of serious people set as their main/only purpose the creation of a efficient D2 compiler. "Performance" is not something that just happens, you need lot of focused work to gain it.


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