Re: SIGFPE and -mieee

[Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>]

Kelledin <kelledin+DAXP@skarpsey.dyndns.org> writes:

> Also, one other detail I forgot: what about EV6 and higher?  My 
> understanding is that on Alpha processors >=EV6, -mieee is 
> either unnecessary, or the extra code it introduces comes at 
> negligible cost.

The latter. The trap barriers introduced by -mieee are discarded as
nops very early in the pipeline, since the ev6 has precise traps.
Also, it can do some more denormal arithmetic in hardware. Example:

double x = 1.0;
for (int i = 0; i < 1000000000; ++i)
    x *= 2;

no -mieee       SIGFPE
-mieee on ev5   165.81 seconds (inf arithmetic emulated by kernel)
-mieee on ev6     1.03 seconds

If you use -mcpu=ev6, -mieee should be totally free since gcc doesn't
insert any trap barriers then.

-- 
	Falk