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cfdf805286
Before this change, the backend was unable to fold a build_vector dag node with UNDEF operands into a single horizontal add/sub. This patch teaches how to combine a build_vector with UNDEF operands into a horizontal add/sub when possible. The algorithm conservatively avoids to combine a build_vector with only a single non-UNDEF operand. Added test haddsub-undef.ll to verify that we correctly fold horizontal binop even in the presence of UNDEFs. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211265 91177308-0d34-0410-b5e6-96231b3b80d8