patterns generated by clang for transpose of a matrix in generic vectors. This is made
of two parts:
1) Propagating vector extracts of hi/lo half into their users
2) Recognizing an insertion of even elements followed by the odd elements as an unpack.
Testcase to come, but this shrinks the # of shuffle instructions generated on x86 from ~40 to the minimal 8.
llvm-svn: 110734
Nate Begeman