From VMS to UNIX

[JTW%mit-xx at sri-unix.UUCP]

From:  John T. Wroclawski <JTW at mit-xx>

	Now wait a cotton picken minute.  How can you say that BLISS produces
	better code than C.  That is an entierely implementation dependant
	thing contingient on what machine you are running on, which version of
	the compiler you are using and what level of optimization you are
	asking it to do.

	-Ron

Fundamental characteristics of the language have an effect, too. The
presence of unrestricted GOTO's in C makes it *much* harder to
implement a really good (read "globally optimizing") C compiler than
an equivalent BLISS compiler. That's one of the main reasons BLISS
left them out.

The only widely available C I've seen in this category is the DEC VMS
compiler. Through global optimization and clever use of the VAX's more
complex addressing modes it generates code with far fewer instructions
than, say, the 4.1BSD version of PCC. It is not, however, as good as
BLISS.  The original BLISS-11 generates positvely amazing code.

It is interesting to note that this is not necessarily relevant. I
have seen at least one case where the VMS compiler generated a code
sequence almost 70% shorter (instruction count) than the 4.1 compiler
for a critical C function, but the code didn't run any faster due to
the VAX's slowness with it's more complicated instruction forms.
More global optimizations would, of course, likely have a more noticable
effect.

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