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long double and i386 optimization
- To: egcs at basil dot cygnus dot com
- Subject: long double and i386 optimization
- From: Jan Hubicka <hubicka at horac dot ta dot jcu dot cz>
- Date: Fri, 5 Sep 1997 12:10:17 +0200
Hi
I have noticed quite strange think: Main mset calculation loop should
be (IMO) exactly same with long double as with double, since whole
calculation is done in register and no memory is accesed and i386
uses "long double" in FPU registers. So I wonder why mset loop compiled
with -O3 -fomit-frame-pointer -mpentium -funroll-loops
is slower in long double than in double, since one extra fxch (or fld
from register I am not sure) is added. Also intructions are scheduled
in a bit different order so result is quite significant(10%) slowdown.
I may send sources too if someone is interested.
Honza
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