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On Tue, 2003-07-15 at 13:58, Dale Johannesen wrote:My patch does not fix the real problem in the aliasing code, but
neither does
Jim's patch, as Franz has demonstrated; from that point of view they're
equally
hackish.
This seems confused. Which one of my patches are you talking about?
The alias.c patch or the loop.c patch? It is already known that the
loop.c patch does not fix 11319 and 10021. Franz never said anything
about my alias.c patch, so he could not have demonstrated that it didn't
fix anything. Also, I don't see how either of my patches could be
described as hackish. My loop.c patch fixes an obvious regression
introduced by an earlier patch from David Miller. My alias.c patch
fixes the code to work as documented.
Mine does fix more of the known occurrences of the bug and does not introduce a performance regression; there are grounds for considering it superior, IMO.
Also, this talk about performance regressions is misleading. The bug
here is that loop is performing unsafe optimizations due to incorrect
alias analysis. If we fix that bug, then obviously we are going to have
performance regressions. This is unavoidable because of the nature of
the bug. Thus both my alias and loop patches cause performance
regressions. Your patch causes less performance regression because it
doesn't fix the underlying bug, it just works around it in some cases.
On the plus side, I have explained how to fix the loop optimizer to get
back the performance lost by the alias fixes.
Roger Sayle's mentioned an x86 regression in a different thread, that appears to be due to my loop.c patch. I don't think anyone has proven it yet, but it is likely to be my patch. This was a 3-4% performance loss on x86 SPECfp.
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