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From: mash@mips.UUCP (John Mashey)
Newsgroups: comp.sys.ibm.pc,comp.lang.c
Subject: Re: Inline assembler; a quiz
Message-ID: <464@winchester.UUCP>
Date: Fri, 19-Jun-87 03:41:26 EDT
Article-I.D.: winchest.464
Posted: Fri Jun 19 03:41:26 1987
Date-Received: Mon, 22-Jun-87 01:35:16 EDT
References: <608@zen.UUCP> <2299@hoptoad.uucp> <21211@sun.uucp>
Reply-To: mash@winchester.UUCP (John Mashey)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 39
Xref: mnetor comp.sys.ibm.pc:4963 comp.lang.c:2560

In article <21211@sun.uucp> guy%gorodish@Sun.COM (Guy Harris) writes:
>> >asm("<assembler code>");
>>    Isn't this spo'sta be apart of the "Standard C".  I seem to remember
>> it being metioned in the K&R.
>It is absolutely NOT supposed to be in standard C!

	.... Guy gives good list of reasons why not....
In support of at least one, our code generator normally passes its output
to the assembler in binary form, although assembler can be generated.
Use of asm would of course force the less efficient form, or force the
code generator to parse the asm statement itself, a distasteful thought.

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.  The same variable may well appear
	in several different places during the code.
	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.

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?
	b) What global optimizers do people use to compile their 
	UNIX kernels? i.e., which of them have implemented "volatile",
	without which device drivers are not easy.

Having used both asm and serious optimizers, I know which I'd rather have.
-- 
-john mashey	DISCLAIMER: <generic disclaimer, I speak for me only, etc>
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