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...If the comparison couldn't solely be determined by > > looking at the other operand, the result is poison. > > This means we cannot do the C-style optimization "int a = ...; a < > (a + 1)" ==> "true". In the case "a + 1" overflows, a is > INT_SIGNED_MAX. But if a is INT_SIGNED_MAX, "a < X" is always false, > for all values of X. So "a < a + 1" is defined; and it is true for "a > != INT_SIGNED_MAX" but false for "a == INT_SIGNED_MAX". Hence the > expression cannot be folded to true. > Th...

Hello, What follows is my attempt to describe how poison works. Let me know what you think. -- David # LLVM Poison Semantics Poison is an LLVM concept which exists solely to enable further optimization of LLVM IR. The exact behavior of poison has been, to say the least, confusing for users, researchers and engineers working with LLVM. This document hopes to clear up some of the confusion