Re: C as assembly language

I would like to point out that some of the problems of C as an
assembly language are just wrong, using the specific example of the
lcc-win32 system. No environment is "perfect" but I think lcc-win32
comes close, and is widely used as a back end compiler.


> Hmm... there are a few additional cases where C is simply inappropriate:
> 1) You want to check for integer overflow.


Under lcc-win32 you just write
        c = a+b;
        if (_overflow()) {
                // Overflow handling
        }
> 2) You need exceptions.


lcc-win32 lets you use the exceptions defined by the OS.
The setjmp/longjmp facility allows you to implement any exception schema you
need.


> Oh, and slightly off-topic, there are a few other things that annoy
> those who want to use C as a backend for their compiler:
> 3) It has no support for tail call recursion.


Not very difficult to implement in the generated C with a few assignments
and a goto...


> 4) It has no support for automatic garbage collection.


lcc-win32 features an automatic garbage collector (Boehm's)


> (The following are from http://www.cminusminus.org/faq.html:)
> 5) It cannot return multiple values in registers
Multiple values in registers?
In general C shields you from assembly. The register layout is defined by
the compiler. Nothing prevents you from building your own schemas of course.


> 6) It cannot bind global variables to registers
In the x86, with only 6 registers this would be impossible, but in other
architectures, the C compiler lets you assign globals to the global
registers with some compiler specific syntax.


> 7) It has no support for lightweight concurrency


Well, under windows you can use the thread facility of the operating system.
Lcc-win32 supports it of course.


>
> Not all of these features are required for each language, but many
> (most?) languages need at least one of them.


lcc-win32 is used as a back end for Objective C Eiffel and other
customer specific languages.


But a language system is not the compiler back end only. When looking
at the alternatives you should include the existence of a configurable
linker and above all a configurable debugger. It is those features
that make actually a system usable as a back end or not. The compiler
is just a part of it.

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