[X86] Add masked MCVTSI2P/MCVTUI2P ISD opcodes to model the cvtqq2ps cvtuqq2ps nodes that produce less than 128-bits of results.

These nodes zero the upper half of the result and can't be represented with vselect.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351666 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed