Date: Wed, 26 Mar 2003 14:58:27 -0600 (CST) From: Loren James Rittle <rittle@latour.rsch.comm.mot.com> To: freebsd-current@freebsd.org Subject: Re: optimization/10189: pentium4 breaks suns libm code for __ieee754_pow(double x, double y) Message-ID: <200303262058.h2QKwR9Z061914@latour.rsch.comm.mot.com> In-Reply-To: <20030326174535.GA83816@dragon.nuxi.com> References: <20030326130118.8374.qmail@sources.redhat.com>
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> Beautiful email!! Thanks David but, although the exact words are mine, I felt deja vu while writing them. I have been asked to contribute it to the gcc bug reporting docs as a warning against using the compiler in novel modes unless you actually first test it as I will describe. Then we will ask all reporters of CPU switch PRs whether they did or can do that test before attempting to stare at a full package/kernel failure mode. I will attempt to be a little more pro-active in watching the GNATS at gcc.gnu.org for FreeBSD. There appears to be an near endless supply of people that wish to add these CPU flags to kernel builds. ;-) >> Special secret #2: Although the FSF-side does want to improve all >> code generation (and I think proper PRs RE CPU switches will be >> looked at by someone given enough time) be aware that -O2 without >> special arch flags is probably the most stable for any given CPU >> for any given gcc release. Do you really want to trust a kernel >> built with optimization flags and arch flags that near zero or zero >> people have fully tested? Doubtful. However, inline with secret >> #1 and by virtual of being digital, if even one person tests it >> (i.e. yourself) and it appears OK, then it is probably safe to at >> least attempt to build a kernel and run it. > FreeBSD has for years recommended -O[1] vs. -O2. Do you think there is > value in having the GCC test suite runs you do at FreeBSD.org do runs > with both settings? Actually (slight backpettle), all of the modern DG test suite in gcc are run at the broad range of -O0,1,2,3. OTOH, by default, everyone is bootstrapping the compiler at -O2 everyday. > To also do runs with the newer CPU types? This would be quite revealing. I would like to extend the automatic regression checkers to cover that but, yow, I'm already eating a lot of cycles on those machines. Added to list of things to check. Regards, Loren
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