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Re: loop optimized in 4.7.2, not in 4.8.1?
- From: Anthony Foiani <tkil at scrye dot com>
- To: Oliver Kullmann <O dot Kullmann at swansea dot ac dot uk>
- Cc: <gcc-help at gcc dot gnu dot org>
- Date: Sun, 11 Aug 2013 02:21:38 -0600
- Subject: Re: loop optimized in 4.7.2, not in 4.8.1?
- References: <geha1qef1 dot fsf at dworkin dot scrye dot com> <20130811005455 dot GK6427 at csltok dot swansea dot ac dot uk>
- Reply-to: Anthony Foiani <tkil at scrye dot com>
Oliver --
Sorry for the confusiong:
Oliver Kullmann <O.Kullmann@swansea.ac.uk> writes:
> On Sat, Aug 10, 2013 at 06:06:26PM -0600, Anthony Foiani wrote:
> > They noticed that their earlier compiler (4.6.3 -O3) successfully
> > reduced the loop, while 4.8.1 didn't.
> For general enligthenment, could you quickly explain what "reduce
> the loop" means? One can of course just get rid off the loop,
> precomputing sum,
That's exactly what I meant. Apologies for not knowing the correct
phrasing.
> which is, at least for me, an unexpected difference? (I would have
> assumed that, if there is a difference, then Index=UInt should be
> faster.)
Seeing only a 15% difference, you probably want to run it multiple
times and average out the values.
Intuitively, I agree that the unsigned loop variable should be faster,
but I have no idea what's actually going on behind the scenes there.
Best regards,
Anthony Foiani