On Sat, Jun 6, 2020 at 3:50 PM Doug McIlroy <doug@cs.dartmouth.edu> wrote:

> > Steve Johnson's position paper on optimising compilers may amuse you:
> > https://dl.acm.org/doi/abs/10.1145/567532.567542
>
> Indeed. This passage struck a particular chord:
>
> "I contend that the class of applications that depend on, for example, loop
> optimization and dead code elimination for their efficient solution is of
> modest size, growing smaller, and often very susceptible to expression in
> applicative languages where the optimization is built into the individual
> applicative operators."
>
> I don't know whether I saw that note at the time, but since then I've
> come to believe, particularly in regard to C, that one case of dead-code
> elmination should be guaranteed. That case is if(0), where 0 is the
> value of a constant expression.
>
> This guarantee would take the place of many--possibly even
> most--ifdefs. Every ifdef is an ugly intrusion and a pain to read.
> Syntactically it occurs at top level completely out of sync with the
> indentation and flow of text. Conversion to if would be a big win.
>

I'd love something like this to work, but the semantic interpretation would
need to also somehow be omitted, otherwise how do you replace

#ifdef AIX
ioct(fd, AIX_SPECIFIC_IOCTL, ...)
#endif

on a HUPX system that doesn't define AIX_SPECIFIC_IOCTL...

I remember hearing that BLISS could cope because it deferred the semantic
interpretation of the identifiers until after a round of dead code
elimination so it didn't need a pre-processor...

Warner