On Sat, Jun 6, 2020 at 5:50 PM Doug McIlroy <doug(a)cs.dartmouth.edu> wrote:
Johnson's position paper on optimising compilers may amuse you:
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
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.
This came up on this list back in 2017 and I posted something about this at
If the language had been extended to support a "compile-type conditional"
syntax ("if #(LINUX)", for example) it would have obviated the need for
most preprocessor conditionals. As long as, syntactically, the compiler
could tokenize a block in absence of e.g. type definitions, dead-code
elimination could do the job.
- Dan C.