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Re: AMD Athlon support
- To: Jan Hubicka <hubicka at atrey dot karlin dot mff dot cuni dot cz>
- Subject: Re: AMD Athlon support
- From: Richard Henderson <rth at cygnus dot com>
- Date: Thu, 30 Sep 1999 18:30:29 -0700
- Cc: egcs-patches at egcs dot cygnus dot com
- References: <19990929124607.03642@atrey.karlin.mff.cuni.cz>
On Wed, Sep 29, 1999 at 12:46:07PM +0200, Jan Hubicka wrote:
> ! /* The Athlon handle ffree instruction as internal NOP, so using it
> ! to pop the top of stack is preffered over the fstp %st(0) one.
> !
> ! The AMD Athlon Code Optimization Note recommend usage of this
> ! instructions and warns about bad documentation of it in the past.
> ! It says that instruction works on all CPUs in x86 CPU familly but
> ! says that it is not supported by some assemblers. I am not sure
> ! about AT&T compatible assemblers. Maybe we can restrict it to the
> ! gas, where it works. */
"ffree %st0" and "fstp %st0" are not the same operation. ffree marks
the register as free, but does not affect the stack-top pointer.
It would be possible to enhance reg-stack to kill %st7 (or whatever
the current bottom of the stack is) this way though. That would save
an fxch+fstp pair...
r~