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Re: [EGCS] Optimizations
- To: egcs at cygnus dot com
- Subject: Re: [EGCS] Optimizations
- From: meissner at cygnus dot com
- Date: Sun, 14 Dec 1997 17:30:48 -0500 (EST)
- Reply-To: egcs at cygnus dot com
| Marc Lehmann wrote:
| > -fschedule-insns is a *loss* on x86 cpu's!
|
| care to explain why it is a loss (and most probably also -fschedule-insns2)
The problem is that -fschedule-insns, -funroll-{,all-}loops, and
-fstrength-reduce all tend to work by creating more registers to hold
intermediate results (in compiler speak this is known as register pressure).
Obviously, -fschedule-insns2 doesn't suffer from this problem, since it only
schedules things after register allocation has been done (and thus on a machine
that has plenty of registers has little effect, other than to move spills
around).
--
Michael Meissner, Cygnus Solutions (Massachusetts office)
4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA
meissner@cygnus.com, 617-354-5416 (office), 617-354-7161 (fax)