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Re: FLOATING-POINT CONSISTENCY, -FFLOAT-STORE, AND X86
- To: burley at gnu dot org (Craig Burley)
- Subject: Re: FLOATING-POINT CONSISTENCY, -FFLOAT-STORE, AND X86
- From: Joe Buck <jbuck at Synopsys dot COM>
- Date: Mon, 14 Dec 98 9:23:52 PST
- Cc: moshier at mediaone dot net, egcs at cygnus dot com, burley at gnu dot org
What would the performance cost be if we spilled ix86 FP registers
as 80 bits? Unfortunately I'm not familiar enough with the ix86
instruction set to answer this question for myself. How difficult
would it be to change gcc to do 80 bit spills, without changing
the size of float and double?
It seems to me that it should cost a lot less than -ffloat-store
and should get rid of the unpredictable behavior. (Yes, it still
doesn't match IEEE unless more is done, but it stops weirdness like
root-finding algorithms that fail to converge if you're unlucky).