[aarch64-port-dev ] RFC: Many patterns for AArch64 instructions

[Andrew Haley]

http://cr.openjdk.java.net/~njian/8158361/webrev.01/

This patch includes patterns for all of the wild 'n wacky combinations
of adds, subtracts, and shifts that AArch64 can execute, even some
rather unikely ones.

I think that we should include them all.  Doing so will slow down the
DFA in C2 that does the pattern matching, but only by a litte bit.  We
do want instructions like

     add    x0, x3, w2, sxtw #3

which is a typical array-indexing operation, even though the sxtb and
sxth variations are unlikely to be useful.

So, should we cull these patterns down to a useful subset or just
push the lot for the sake of completeness?

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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