A way to significantly speed up compiles?

[Michael Meissner]

In article <1037 at gistdev.gist.com> flint at gistdev.gist.com (Flint
Pellett) writes:

| This is a proposal on how to make C compiles a lot faster, but it may
| not be a useful enough case to be worth it for typical C programs.
| I thought I'd throw the idea up for discussion though.  Consider the
| following sample of code:
| 
| #define	STARTLOC	0
|  <..10 things..>
| #define ENTRY1		STARTLOC + 10
|  <..5 things..>
| #define ENTRY2		ENTRY1 + 5
|  <..7 things..>
| #define ENTRY3		ENTRY2 + 7
| ...
| int pointers[] = {STARTLOC,ENTRY1,ENTRY2,ENTRY3...
| 
| I expected the output of cpp to look like this:
| 
| int pointers[] = {0 , 10 , 15 , 22 , ...
| 
| cpp, however, is only doing simple text substitution here, and produced:
| 
| int pointers[] = {0 , 0+10 , 0+10+5 , 0+10+5+7 , ...
| 
| If you're trying to use MSC5.1 it doesn't even work: after you get
| somewhere around ENTRY60, it quits, telling you you've tried to nest
| your constants too deeply.  The questions is, why not have cpp combine
| those numbers at pre-processor time?  Wouldn't it make a lot more
| sense to have cpp add 0+10+5+7 together once when ENTRY3 is #defined
| in cpp rather than making the compiler add those numbers together 100
| times in the 100 places that ENTRY3 is used? 

Why not use an enumeration instead of lots of defines (unless of
course you have a PCC-derived compiler and more than 150 defines)?

This 'optimization' will buy you so little, I doubt you could measure
it.  In fact, I would suspect that it will actually slow things down
(making the preprocessing MUCH more complex in order to shave a few
milliseconds off of the compiler proper).
--
Michael Meissner	email: meissner at osf.org		phone: 617-621-8861
Open Software Foundation, 11 Cambridge Center, Cambridge, MA, 02142

Considering the flames and intolerance, shouldn't USENET be spelled ABUSENET?