Merging r213799:
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r213799 | grosbach | 2014-07-23 13:41:38 -0700 (Wed, 23 Jul 2014) | 5 lines

X86: restrict combine to when type sizes are safe.

The folding of unary operations through a vector compare and mask operation
is only safe if the unary operation result is of the same size as its input.
For example, it's not safe for [su]itofp from v4i32 to v4f64.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_35@214841 91177308-0d34-0410-b5e6-96231b3b80d8
Add blurb about LDC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_35@214842 91177308-0d34-0410-b5e6-96231b3b80d8