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Re: Draft "Unsafe fp optimizations" project description.
- To: dewar at gnat dot com, toon at moene dot indiv dot nluug dot nl
- Subject: Re: Draft "Unsafe fp optimizations" project description.
- From: dewar at gnat dot com
- Date: Sun, 5 Aug 2001 18:30:44 -0400 (EDT)
- Cc: gcc at gcc dot gnu dot org, lucier at math dot purdue dot edu, tprince at computer dot org
<<It all depends on what you mean by "now". -ffast-math (no c :-) enables
underflow-to-zero on ia64 and alpha. On my alpha (I've never even seen
a ia64 workstation, but they seem to exist), forcing the processor to
treat underflow-as-zero meant an 1.8 times speed up on our Numerical
Weather Forecasting system.
>>
Sure but that is exatly the case we know is highly significant on this
processor, what is interesting is to know if *any* of the other transformations
have any effect at all.
For my taste I would have underflow-to-zero be the default on alpha, and
only use the very expensive denormal stuff if -mieee is set.