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While debugging GVNHoist, I found it confusing that the entries in a VNtoInsns were not always value numbers. They _usually_ were except for StoreInst in which case they were a hash of two different value numbers. This leads to two observations: - It is more difficult to debug things when the semantic contents of VNtoInsns changes over time. - Using a single value number is not much cheaper, the value of VNtoInsns is a SmallVector. - It is not immediately clear what the algorithm would do if there were hash collisions in the StoreInst case. Using a DenseMap of std::pair sidesteps all of this. N.B. The changes in the test were due their sensitivity to the iteration order of VNtoInsns which has changed. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275761 91177308-0d34-0410-b5e6-96231b3b80d8