[PATCH 1/n] Add conditional compare support

Richard Henderson rth@redhat.com
Thu Oct 24 17:28:00 GMT 2013

On 10/24/2013 09:37 AM, Richard Earnshaw wrote:
> It still needs to put out the right final condition based on the
> comparisons that were previously done.  At least traditionaly (in the
> existing ARM code) the comparison was just EQ or NE even if the original
> tests were inequalities; so the only way to convey the real comparison
> information was through the condition code (where select_cc_mode could
> work out what was really needed).
> I guess if the branch had more information about the comparison, then
> the need to encode information through CC mode; but it's always been the
> case that the CC mode can modify the final branch condition needed in
> the instruction -- consider for example use of bpl vs bge for
> non-overflowing >= 0 tests.

Yes, the arm flags are not so dissimilar to i386 flags in that way.

In the i386 port, we do use the "real" comparison code plus a CCmode
in order to select between branches.

I missed the fact that these modes are pre-existing in the arm backend,
wrongly assuming that the ccmp patches were adding them.  Thus all my
comments on the subject are spurious.


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