Optimization (was Re: volatile)

[Every system needs one]

In article <310 at zinn.MV.COM>, mem at zinn.MV.COM (Mark E. Mallett) writes:
| In article <3938 at killer.UUCP>, chasm at killer.UUCP (Charles Marslett) writes:
| > In article <13074 at brl-adm.ARPA>, dsill at NSWC-OAS.arpa (Dave Sill) writes:
| > > Terry Lambert writes:
| > > 
| > > This bears repeating.  There should be no circumstances under which
| > > the semantics of the language are changed by a flag to the compiler.
| 
| Avoiding the word "semantics", -O can change the way the program
| operates, which is what is important in this discussion.
| 
| And if you don't think that the semantics of the language can be changed
| by a flag to the compiler, well... what about "-D" ??

Mark:

	First:	I am the one being repeated, not doing the repeating.
	Second:	The statement being repeated did NOT deal with all
		options; only -O... it was:

|Basically, if it works without -O, it should work with -O, regardless of what
|the compiler writer's optimization does to achieve its goal.  If this makes
|writing compilers harder, so what?

	Third:	The point was that while a transform based -O is most likely
		a non-reversable one, no information should be lost due to
		bad assumptions made by the compiler writer, and that ANSI
		C was a cop-out by compiler writers who wanted the hard
		work of determining volatility and aliases, as well as
		other information useful for optimization, done by the
		programmer.  I simply suggested that I could not see one
		instance of where it was conceptually impossible for a
		compiler writer to determine these things; just damn hard.
		My point was "better the compiler writer than the compiler
		user".


| Terry Lambert           UUCP: ...{ decvax, ihnp4 } ...utah-cs!century!terry |
| @ Century Software        OR: ...utah-cs!uplherc!sp7040!obie!wsccs!terry    |
| SLC, Utah                                                                   |
|                   These opinions are not my companies, but if you find them |
|                   useful, send a $20.00 donation to Brisbane Australia...   |
| 'Admit it!  You're just harrasing me because of the quote in my signature!' |