[X86][SSE] Vectorize a bit (AND/XOR/OR) op if a BUILD_VECTOR has the same op...

[X86][SSE] Vectorize a bit (AND/XOR/OR) op if a BUILD_VECTOR has the same op for all their scalar elements.

If all a BUILD_VECTOR's source elements are the same bit (AND/XOR/OR) operation type and each has one constant operand, lower to a pair of BUILD_VECTOR and just apply the bit operation to the vectors.

The constant operands will form a constant vector meaning that we still only have a single BUILD_VECTOR to lower and we will have replaced all the scalarized operations with a single SSE equivalent.

Its not in our interest to start make a general purpose vectorizer from this, but I'm seeing enough of these scalar bit operations from the later legalization/scalarization stages to support them at least.

Differential Revision: http://reviews.llvm.org/D18492

llvm-svn: 264666