Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!decwrl!ucbvax!ucsfcgl!pixar!mccoy
From: mccoy@pixar.UUCP (Daniel McCoy)
Newsgroups: comp.unix.ultrix
Subject: Re: Warning! Compiler Bug (DecSt.3100)
Message-ID: <7830@pixar.UUCP>
Date: 22 Nov 89 22:06:11 GMT
References: <458@tron.UUCP> <473@contex.UUCP>
Reply-To: mccoy@pixar.UUCP (Daniel McCoy)
Organization: Pixar -- Marin County, California
Lines: 16

In article <473@contex.UUCP> chris@contex.UUCP (Chris Anderson) writes:
>The following program, when compiled on the DecStation 3100,
>produces d=0, when it should be d=1:
>
>    unsigned a = 2, d;
>    int b = 1, c = 1;
>
>    d = (c >= (b - a + 1));
 ...
>(Note, this happens even without -O). Voila! Bad code.

It is the optimizer.
The default optimization level is -O1
The program produces d=1 when compiled with -O0 to turn off all optimization.

Dan McCoy     Pixar       {ucbvax,sun}!pixar!mccoy