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From: Andrew Gallatin <gallatin@cs.duke.edu>
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Date: Thu, 23 Mar 2000 11:04:22 -0500 (EST)
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!)
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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 


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