Simon Pilgrim ebbbdf51f2 [X86][AVX2] Fix v16i16 SHL lowering (PR27730)
The AVX2 v16i16 shift lowering works by unpacking to 2 x v8i32, performing the shift and then truncating the result.

The unpacking is used to place the values in the upper 16-bits so that we can correctly sign-extend for SRA shifts. Unfortunately we weren't ensuring that the lower 16-bits were zero to ensure that SHL correctly shifts in zero bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@271796 91177308-0d34-0410-b5e6-96231b3b80d8
2016-06-04 16:45:33 +00:00
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