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Re: [CFG] Loop unrolling
- From: law at redhat dot com
- To: Jan Hubicka <jh at suse dot cz>
- Cc: gcc-patches at gcc dot gnu dot org, gcc-pdo at atrey dot karlin dot mff dot cuni dot cz
- Date: Tue, 05 Mar 2002 16:22:01 -0700
- Subject: Re: [CFG] Loop unrolling
- Reply-to: law at redhat dot com
In message <20020228083032.GC706@atrey.karlin.mff.cuni.cz>, Jan Hubicka
writes:
> Signed counters are undefined on overflow, but unfortunately enought we
> don't have that information at unroll time, so we must be conservative.
Also be aware that while technically invalid, some code has been very
sensitive to overflows in the loop optimizer -- specifically the Linux
kernel. Avoiding an overflow issue is precisely why the linux kernel
builds with -fno-strength-reduce.
Be very very very careful with assuming that we can safely overflow.
jeff