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From: bright@dataio.Data-IO.COM (Walter Bright)
Newsgroups: comp.sys.ibm.pc,comp.lang.c
Subject: Re: Inline assembler; a quiz
Message-ID: <1323@dataio.Data-IO.COM>
Date: Tue, 23-Jun-87 13:51:30 EDT
Article-I.D.: dataio.1323
Posted: Tue Jun 23 13:51:30 1987
Date-Received: Thu, 25-Jun-87 02:14:28 EDT
References: <608@zen.UUCP> <2299@hoptoad.uucp> <21211@sun.uucp> <464@winchester.UUCP>
Reply-To: bright@dataio.UUCP (Walter Bright)
Organization: Data I/O - FutureNet Corp., Redmond, WA
Lines: 31
Xref: mnetor comp.sys.ibm.pc:5025 comp.lang.c:2614

In article <464@winchester.UUCP> mash@winchester.UUCP (John Mashey) writes:
<More important:
<And finally, "asm" and global-optimizing compilers are fairly
<contradictory.  A good optimizer:
<	a) Mostly ignores register declarations. It allocates
<	registers as appropriate.
Datalight C can even allocate more than one variable to a specific register,
if their usages do not overlap. This is known as 'register allocation by
coloring'.
<	b) May, given slightly different source code, rearrange the
<	register use substantially.
<	c) Will find it VERY hard to figure out what an arbitrary
<	"asm statement" is doing, in terms of side-effects.
It's not that hard. Assuming that the asm doesn't contain jumps out of
or into itself, flow analysis can be done over asm statements by assuming
that they can but not necessarilly do modify everything.
<Finally, some questions:
<	a) What global optimizing C compilers do people use out there?
<		Known ones: MIPS, Green Hills, Sun's, DEC [newest Ultrix
<		one, I think], Multiflow, Tartan Labs, newest IBM one
<		for RT PC, HP's Spectrum compiler.
<		Any others? Any for PC's?

The Datalight C compiler is a globally optimizing compiler. It does
most of the classic global optimizations that depend on data flow analysis.
For example, it does constant propagation, copy propagation, very busy
expressions, partially redundant expressions, loop induction variables,
register allocation by coloring, etc.

Disclaimer: I have no association with Datalight other than the fact that
I wrote the compiler and receive money for it.