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It's not safe to use the two value CombineTo variant to combine away a dead load. e.g. v1, chain2 = load chain1, loc v2, chain3 = load chain2, loc v3 = add v2, c Now we replace use of v1 with undef, use of chain2 with chain1. ReplaceAllUsesWith() will iterate through uses of the first load and update operands: v1, chain2 = load chain1, loc v2, chain3 = load chain1, loc v3 = add v2, c Now the second load is the same as the first load, SelectionDAG cse will ensure the use of second load is replaced with the first load. v1, chain2 = load chain1, loc v3 = add v1, c Then v1 is replaced with undef and bad things happen. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46099 91177308-0d34-0410-b5e6-96231b3b80d8
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