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From: | Edmund Grimley Evans |
Subject: | Re: [Tinycc-devel] [PATCH] tccgen.c: Optimise 0<<x, 0>>x, -1>>x, x&0, x*0, x|-1, x%1. |
Date: | Fri, 6 Mar 2015 08:11:39 +0000 |
User-agent: | Mutt/1.5.21 (2010-09-15) |
Vincent Lefevre <address@hidden>: > > Do not optimise (0 / x) and (0 % x) here as x might be zero, though > > for an architecture that does not generate an exception for division > > by zero the back end might choose to optimise those. > > When x is 0, this is undefined behavior, so that you are free to > optimize them, even if the architecture generates an exception for > division by 0. Contrary to IEEE 754, there isn't any requirement > to generate an exception for integer operations. Yes, I know, but I would nevertheless prefer (0 / x) to do the same thing as (y / x) when both x and y are zero at run time. That potentially depends on the target architecture. Edmund
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