"Honour Parens" Rule

[anw at nott-cs.UUCP]

In article <796 at garth.UUCP> smryan at garth.UUCP (Steven Ryan) writes:
>> [ stuff about re-arranging expressions ]
> This issue is messier than it appears on the surface. [ more ideas etc ]

	It's even messier than this, and getting messier as time goes on.
Over in "comp.arch", they're talking about optimising assemblers.  We now
have *at least* four places where expressions may be optimised -- in the
compiler, in the intermediate code (in systems such as the Amsterdam
Compiler Kit), in intelligent linkers, and in the assembler (presumably
before *and/or* after linking, depending on how compiled modules are
stored).  I suppose that even optimising loaders are not a totally stupid
idea [I don't mean intelligent pre-paging, more a loader that says, "Hey,
the cache has just been expanded, so that load should be moved to *here*,
and yesterday's benchmark shows that the FP multiply is faster than we
thought, so *that* NOP can be deleted", etc.].

	*Each* of these stages (some of which "cc" *ought* not to know
anything about in most Unix-like systems) *may* now need special directives
to say "Don't mess with this, or it may overflow/alias/volatilate [:-)] in
ways you can't be expected to understand".  This is not easy when the compiler
may (well) have no idea what the target system is.

	Bring back the good old days, when C was defined by what happened
using DMR's compiler on DMR's computer! :-)

-- 
Andy Walker, Maths Dept., Nott'm Univ., UK
anw at maths.nott.ac.uk