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When we delete a live-range, we check if that live-range is the origin of others to keep it around for rematerialization. For that we check that the instruction we are about to remove is the same as the definition of the VNI of the original live-range. If this is the case, we just shrink the live-range to an empty one. Now, when we try to delete one of the children of such live-range (product of splitting), we do the same check. However, now the original live-range is empty and there is no way we can access the VNI to check its definition, and we crash. When we cannot get the VNI for the original live-range, that means we are not in the presence of the original definition. Thus, this check does not need to happen in that case and the crash is sloved! This bug was introduced in r266162 | wmi | 2016-04-12 20:08:27. It affects every target that uses the greedy register allocator. To happen, we need to delete both a the original instruction and its split products, in that order. This is likely to happen when rematerialization comes into play. Trying to produce a more robust test case. Will follow in a coming commit. This fixes llvm.org/PR27983. rdar://problem/26651519 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272314 91177308-0d34-0410-b5e6-96231b3b80d8
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