vme131!lsi4!jecel@uunet.UU.NET writes:

Why is the Self compiler always compared with optimizing C? Since it does many run-time checks I would think that Self would be more fairly compared to Pascal.

When comparing the performance of our Self compiler to other systems, we try to be as honest and fair as possible, in the sense of comparing against the best commonly available system. Comparing against a Pascal compiler that generates slower code with extra run-time checks might make our compiler look better, but wouldn't be as honest. Comparing against the best traditional compiler available (e.g. an optimizing C compiler) will give the results the most validity, and (hopefully) convince the largest number of people that they should switch to a nicer language like Self, now that the run-time performance is close.

Some might argue that we should compare against an optimizing Fortran compiler, since they tend to be better than C compilers. This might be more honest, in the sense of giving us the worst possible comparison. But I would claim that Fortran really isn't a general purpose programming language, and is only used in numerical applications where the limited functionality of the language is adequate. Also, we don't really want to find an optimizer that does a significant number of optimizations, since our Self compiler only includes common subexpression elimination and global register allocation. Presumably we'd have to implement every optimization implemented in a competitor's compiler in order to reach comparable code quality. C seems to be a good thing to compare against, since the language is general purpose, commonly used, and the optimizing compilers produce good code, but without extreme amounts of optimization.

reed.bitnet writes:

And, in the interests of completeness, which C compiler are you comparing against. I don't know about the Sparcstation, but on a Sun 3 you can get a factor-of-two performance improvement simply by using gcc instead of Sun cc.

We use the standard Sun optimizing C compiler. On the SPARC, this compiler is about the same quality as the GCC compiler, a least the last time we compared them (a couple of years ago).

vme131!lsi4!jecel@uunet.UU.NET writes:

I don't like C++ very much - couldn't the Self compiler be written in Self ( which, I hope you will agree, is much nicer ) and compile itself using a tiny bootstrap interpreter?

We've been asked that question many times. When we first designed the language, we didn't know whether we'd be able to reach Smalltalk performance, let alone C performance, so bootstrapping was never considered. However, even if we were to reimplement our compiler in Self, there are still some tricky issues left. One is the fact that the compiler's compiled code would be in the code cache, and so might get flushed, in which case the system would have to fall back to the interpreter to interpret the Self compiler to compile some application code. This could make compiler pauses very distracting. Also, bugs in the Self compiler could be very difficult to find, especially if it compiles itself. Finally, there would be a large dependency between the Self code and the virtual machine. The Self compiler would have to communicate a lot of information to the virtual machine, and vice versa, in order to generate the same high quality code. Designing the interface between the virtual machine and the Self compiler is a hard problem.

vme131!lsi4!jecel@uunet.UU.NET writes:

Are there any statistics on Self like those on Smalltalk in "Smalltalk-80: Bits of History, Words of Advice"? I'm designing a Self multiprocessor machine and knowing such things as average object size and so on would be helpful.

No real statistics yet. I'd imagine that Self objects look a lot like Smalltalk objects. Perhaps a bit smaller because of differences in coding styles. The major differences would have to do with statistics related to the execution engine and method lookup, which could be wildly different with our optimizing compiler.

-- Craig Chambers