Re: How `export' could be useful

Walter Bright <>
24 Apr 2006 16:06:16 -0400
Andrei Alexandrescu (See Website For Email) wrote:

James Kanze wrote: wrote:

By creating pointer aliases, you can prevent the optimization
of binding certain variables to registers, but that doesn't
mean this type of optimization is impractical or undesirable.
Optimizations that are only possible if good or typical
programming practice is followed can still be useful.

Providing you can handle the alternative cases as well. (I've
seen this in optimizers : in one case I've seen, any violation
of SESE caused the optimizer to give up completely. Presumably,
the author of this compiler felt even stronger about SESE than I

Let me guess: the compiler was distributed on 360 KB floppy disks.
Because today, such a compiler would be quite useless in wake of
exceptions - just as the SESE way of writing code itself.

There's also no reason to even write an optimizer that way. Algorithms
that don't require SESE, and don't compromise on results, have been
around since at least the 1970's.

[Anecdote: back in the 80's, when dinosaurs ruled the earth, I was on a
C compiler vendor panel at SDWest. The first question asked was "do you
have a version of the compiler that will work on a floppy disk only
computer?" Down the line, each compiler vendor pontificated on how they
had a special configuration that would work on floppies. Then it got to
me. I said that our floppy only compiler version cost $200 extra and
came with a hard disk. That was the end of that, and the question never
came up again <g>.]

It wasn't until 1992 or 93, though, that we were finally able to abandon
distributing the compiler on floppies, when CD drives became ubiquitous
enough. And just in time, too, juggling a dozen or more floppies was a
big pain for everyone.

Even so, the very first data flow analysis optimizing compiler I wrote,
back in 1985 or so, did not rely on SESE (or even care about it).

-Walter Bright C, C++, D programming language compilers

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