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to "C ^ 1" is only valid when C is known to be either 0 or 1. Most of the similar foldings in this function only handle "i1" types, but this one appears intentionally written to handle larger integer types. If C has an integer type larger than "i1", this needs to check if the high bits of a boolean are known to be zero. I also changed the comment to describe this folding as "C ^ 1" instead of "~C", since that is what the code does and since the latter would only be valid for "i1" types. The good news is that most LLVM targets use TargetLowering::ZeroOrOneBooleanContent so this change will not disable the optimization; the bad news is that I've been unable to come up with a testcase to demonstrate the problem. I have also removed a "FIXME" comment for folding "select C, X, 0" to "C & X", since the code looks correct to me. It could be made more aggressive by not limiting the type to "i1", but that would then require checking for TargetLowering::ZeroOrNegativeOneBooleanContent. Similar changes could be done for the other SELECT foldings, but it was decided to be not worth the trouble and complexity (see e.g., r44663). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62790 91177308-0d34-0410-b5e6-96231b3b80d8
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