Re: auto predicating branches

Stefan Monnier <monnier@iro.umontreal.ca> writes:

Of course, nothing prevents a CPU from doing "predicate prediction":
instead of waiting for an answer to `needle < *base[middle]`, it could
try and guess whether it will be true or false and thus choose to send
one of the two addresses (or both) to the memory (and later check the
prediction and rollback, just like we do with normal branches).

That would subvert the use of predication for getting constant-time
code for avoiding timing side channels.  I.e., not a good idea.

- anton
--
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>