On 2017-11-06 5:45 PM, John David Anglin wrote:
On 2017-11-06 4:27 PM, Helge Deller wrote:
/* Check the validity of the size pointer */
- subi,>>= 4, %r23, %r0
- b,n lws_exit_nosys
+ cmpib,COND(<<),n 3, %r23, lws_exit_nosys
I don't believe that we want to use COND here (i.e., we want a 32-bit
check). We might not
need to trim the upper 32-bits r23.
The reason the code uses nullification is the fast path occurs when
the "b,n" is nullified. So we
avoid the branch prediction penalty. I'd have to check whether the
fast path with the cmpib instruction
is the taken branch or not.
For cmpib with "<<" condition, the hint for a backward branch is likely
taken. The branch to
lws_exit_nosys is backward.
Dave
--
John David Anglin dave.anglin@xxxxxxxx
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