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From: tim@nucleus.amd.com (Tim Olson)
Newsgroups: comp.lang.c
Subject: Re: is this broken or what?
Message-ID: <28900@amdcad.AMD.COM>
Date: 24 Jan 90 03:30:15 GMT
References: <1482@mdbs.UUCP> <1990Jan23.155910.2439@cubmol.bio.columbia.edu>
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Reply-To: tim@amd.com (Tim Olson)
Organization: Advanced Micro Devices, Inc., Austin, Texas
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In article <1990Jan23.155910.2439@cubmol.bio.columbia.edu> ping@cubmol.bio.columbia.edu (Shiping Zhang) writes:
| In article <1482@mdbs.UUCP> wsmith@mdbs.UUCP (Bill Smith) writes:
| >	unsigned u = 0;
| >
| >	if (u-- < 4)
| >		printf("yes\n");
| >	else
| >		printf("no\n");
| >
| >The Data General Aviion 5000 (an 88000 machine) version of GCC converts this 
| >into:
| >
| >	unsigned u = 0;
| >
| >	if(--u < 3) ....
| >
| >for the assembly.
| >
| 
| To me, the codes in the two cases are same.

Check out what happens when u == 0.  Yes, it is an unsafe optimization
which should not be performed.


	-- Tim Olson
	Advanced Micro Devices
	(tim@amd.com)