Date: Thu, 23 Mar 2000 11:04:22 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: Ed Hall <edhall@screech.weirdnoise.com> Cc: obrien@FreeBSD.ORG, freebsd-alpha@FreeBSD.ORG Subject: Re: Compiler problems with -O2 (was Re: CVS Trouble, even under 4.0-RELEASE (alpha) HELP!) Message-ID: <14554.16137.955904.783199@grasshopper.cs.duke.edu> In-Reply-To: <200003230820.AAA12969@screech.weirdnoise.com> References: <gallatin@cs.duke.edu> <14553.19348.115781.273817@grasshopper.cs.duke.edu> <200003230820.AAA12969@screech.weirdnoise.com>
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(-stable and howardl@account.abs.net trimmed from the CC lines) Ed Hall writes: > Andrew Gallatin writes: > : I take it the O2 bugs are not unique to us, but rather they are > : generic across all OSes that gcc version 2.95.2 runs on? Do the gcc > : people know these problems exist? > > Just FYI, the Linux kernel is compiled with: > > -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -mno-fp-regs \ > -ffixed-8 -fno-strict-aliasing > > on Alpha, and seems quite stable with these flags. Yes, this is with > GCC 2.95.2. Any idea if the linux compiler uses the HAIFA optimizer? Perhaps that is our problem. > On applications, I've seen gains of about 20% for the higher levels of > optimization (for example, CSound processes a particular piece in 79 > seconds when compiled with just -O, and 65 seconds with -O2). This is > a useful improvement, though one that has to be balanced with the risks. To me, at least, this is not worth the risk. The Tru64 Compaq C compiler & libraries have sped up a collegue's floating-point intensive matrix manipulation code by a factor of 4. That's the To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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