llvm-project

a6fefc82 - [InstCombine] Convert logical and/or with `icmp samesign` into bitwise ops (#116983)

[InstCombine] Convert logical and/or with `icmp samesign` into bitwise ops (#116983) See the following case: ``` define i1 @test_logical_and_icmp_samesign(i8 %x) { %cmp1 = icmp ne i8 %x, 9 %cmp2 = icmp samesign ult i8 %x, 11 %and = select i1 %cmp1, i1 %cmp2, i1 false ret i1 %and } ``` Currently we cannot convert this logical and into a bitwise and due to the `samesign` flag. But if `%cmp2` evaluates to `poison`, we can infer that `%cmp1` is either `poison` or `true` (`samesign` violation indicates that X is negative). Therefore, `%and` still evaluates to `poison`. This patch converts a logical and into a bitwise and iff TV is poison implies that Cond is either poison or true. Likewise, we convert a logical or into a bitwise or iff FV is poison implies that Cond is either poison or false. Note: 1. This logic is implemented in InstCombine. Not sure whether it is profitable to move it into ValueTracking and call `impliesPoison(TV/FV, Sel)` instead. 2. We only handle the case that `ValAssumedPoison` is `icmp samesign pred X, C1` and `V` is `icmp pred X, C2`. There are no suitable variants for `isImpliedCondition` to pass the fact that X is [non-]negative. Alive2: https://alive2.llvm.org/ce/z/eorFfa Motivation: fix [a major regression](https://github.com/dtcxzyw/llvm-opt-benchmark/pull/1724#discussion_r1849663863) to unblock https://github.com/llvm/llvm-project/pull/112742.