[x86] Teach the new vector shuffle lowering of v4f64 to prefer a direct
VBLENDPD over using VSHUFPD. While the 256-bit variant of VBLENDPD slows
down to the same speed as VSHUFPD on Sandy Bridge CPUs, it has twice the
reciprocal throughput on Ivy Bridge CPUs much like it does everywhere
for 128-bits. There isn't a downside, so just eagerly use this
instruction when it suffices.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218208 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Explicitly lower to a blend early if it is trivial to do so for
v8f32 shuffles in the new vector shuffle lowering code.

This is very cheap to do and makes it much more clear that anything more
expensive but overlapping with this lowering should be selected
afterward (for example using AVX2's VPERMPS). However, no functionality
changed here as without this code we would fall through to create no-op
shuffles of each input and a blend. =]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218209 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Regenerate this test case now that I've improved my script for
generating the test cases to format things more consistently and
actually catch all the operand sequences that should be elided in favor
of the asm comments. No actual changes here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218210 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Begin teaching the new vector shuffle lowering among the most
important bits of cleverness: to detect and lower repeated shuffle
patterns between the two 128-bit lanes with a single instruction.

This patch just teaches it how to lower single-input shuffles that fit
this model using VPERMILPS. =] There is more that needs to happen here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218211 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Add test cases for UNPCK instructions with v8f32 AVX vectors in
preparation for enhancing their support in the new vector shuffle
lowering.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218212 91177308-0d34-0410-b5e6-96231b3b80d8