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dependencies. The basic situation was this: consider if we had: store1 ... store2 ... store3 Where memdep thinks that store3 depends on store2 and store2 depends on store1. The problem happens when we delete store2: The code in question was updating dep info for store3 to be store1. This is a spiffy optimization, but is not safe at all, because aliasing isn't transitive. This bug isn't exposed today with DSE because DSE will only zap store2 if it is identifical to store 3, and in this case, it is safe to update it to depend on store1. However, memcpyopt is not so fortunate, which is presumably why the "dropInstruction" code used to exist. Since this doesn't actually provide a speedup in practice, just rip the code out. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60263 91177308-0d34-0410-b5e6-96231b3b80d8
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