Date: Sun, 2 Mar 1997 18:42:56 -0800 From: jehamby@lightside.com (Jake Hamby) To: henrich@crh.cl.msu.edu, freebsd-chat@FreeBSD.ORG, ghelmer@cs.iastate.edu Subject: Re: RSA 56-bit key challenge Message-ID: <199703030242.SAA01253@hamby1>
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Guy Helmer writes: > On Sun, 2 Mar 1997, Charles Henrich wrote: > > > The binary distribution client performs 346534 keys/sec on my PPro/233 > > > > A GCC-2.6.3 binary performs 390k/sec on a PPro/233 with HAVE_FPU math libs > > A GCC-2.7.2 binary performs 219k/sec on a PPro/233 with HAVE_FPU math libs > > That might help explain some of the differences in numbers for my runs of > SPEC95 fp benchmarks on 2.1.5 (-O2 optimization) w/o HAVE_FPU math libs > vs. 2.2-BETA (-O4 optimization) w/ HAVE_FPU. I ran a few of the fp > benchmarks on 2.2 to compare to my full run under 2.1.5 and found the > codes ran from slightly faster to much slower under 2.2. I figured it was > due to the different math library, but maybe the compiler is more at fault > than I thought... Maybe this has to do with the patch in 2.7.2.1 to disable certain kinds of strength reduction (-fstrength-reduce) because of buggy code generation. Recall that this bug was why FreeBSD changed from using -O2 to -O optimization (although some people used "-O2 -fno-strength-reduce). Here's a quote from David S. Miller, from the "Sun vs. GCC" thread last month: > Also, the various optimizer bugs in GCC in the past have led people > to be wary to use -O2 optimization, much less try additional > optimization flags. > >I know about them, just about all of them are in the strength >reduction pass. I am very familiar with the problematic bugs this >layer has, and I have been actively trying to get people on the GCC >development team to fix them. Almost all of these problems have to do >with when a pointer comparison is converted into an integer invariant >comparison, and vice versa. GCC in certain circumstances does not >notice the change in signed'ness and thus produces incorrect code. In >gcc-2.7.2.1, the strength reduction transformations that were known to >lead to this situation were disabled entirely and in fact this fix was >the entire reason for that release of gcc. -- Jake
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