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From: lindwall@sdsu.UUCP (John Lindwall)
Newsgroups: comp.sys.amiga
Subject: Amiga compiler optimizing test
Keywords: Manx C optimize code
Message-ID: <3531@sdsu.UUCP>
Date: 2 Mar 89 07:00:30 GMT
Organization: San Diego State University, Math/Sciences Dept.
Lines: 44



	This posting was prompted by a friendly competition between two IBM
PC  compilers  - Microsoft C 5.0 and Turbo C 2.0.  We compared the assembly
output  generated  by  these compilers from a simple piece of code (I had a
similar  statement  in a graphics program I was writing at the time).  Here
is the code:

main()
{
	int x, y, z;

	x = 8*y - 8*z;
}


	[Keep reading - this IS an amiga posting.]

	It turned out that MSC generated nicer code for this statement.  It
fetched  y  and  z , performed the subtraction, bit shifted the result, and
stored  the  result  in x.  Turbo fetched y, shifted it, fetched z, shifted
it, subtracted, and stored the result in x.

	So what does this have to do with Amigas?  Well, out of curiosity I
tried  the same test on the only Ami compiler C I have, Manx 3.6a.  Here is
how I compiled it:
	cc -a +L test.c
And here is the code generated:

	move.l	-8(a5),d0	; get y
	asl.l	#3,d0		; y *= 8
	move.l	-12(a5),d1	; get z
	asl.l	#3,d1		; z *= z
	sub.l	d1,d0		; x = 8*y - 8*z
	move.l	d0,-4(a5)

	Just out of curiosity I was wondering if someone could compile this
code  using  Lattice so we can compare results.  Use long integers.  Please
reveal the command line used to perform the compilation.

	Thanks!

johnl@tw-rnd.SanDiego.NCR.COM
john.lindwall@tw-rnd.SanDiego.NCR.COM