On 12-12-07 12:20, [email protected] wrote:
Here are a variety of machines:
Thanks much for all! Collecting all data now...
With -O2, the cycle counts come out (before division) as
out: 0xFFFFFFFFFFEA6F4F
in: 0xFFFFFFFFFCE68BB6
I think the "A" constraint doesn't work quite the same in
64-bit code. The compiler seems to be using %rdx rather than
%edx:%eax.
Yes indeed, that tripped me up. Have been using the "=A" locally for a while
for similar timing tests. Will use a manual "=a" (lo), "=d" (hi) I guess for
amd64 compatibility from now on.
If I'd care deeply I'd probably categorize this as a backwards compatibility
bug in GCC though. Things were probably never guaranteed but they certainly
worked that way...
Rene.
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