[x86] Implement v16i16 support with AVX2 in the new vector shuffle
lowering.

This also implements the fancy blend lowering for v16i16 using AVX2 and
teaches the X86 backend to print shuffle masks for 256-bit PSHUFB
and PBLENDW instructions. It also makes the mask decoding correct for
PBLENDW instructions. The yaks, they are legion.

Tests are updated accordingly. There are some missing tests for the
VBLENDVB lowering, but I'll add those in a follow-up as this commit has
accumulated enough cruft already.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218430 91177308-0d34-0410-b5e6-96231b3b80d8
[X86,AVX] Add an isel pattern for X86VBroadcast.

This fixes PR21050 and rdar://problem/18434607.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218431 91177308-0d34-0410-b5e6-96231b3b80d8
llvm-cov: Combine segments that cover the same location

If we have multiple coverage counts for the same segment, we need to
add them up rather than arbitrarily choosing one. This fixes that and
adds a test with template instantiations to exercise it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218432 91177308-0d34-0410-b5e6-96231b3b80d8