llvm-project

9544bb5c - [InstCombine] Fold umul.overflow(x, c1) | (x*c1 > c2) to x > c2/c1 (#147327)

[InstCombine] Fold umul.overflow(x, c1) | (x*c1 > c2) to x > c2/c1 (#147327) The motivation of this pattern is to check whether the product of a variable and a constant would be mathematically (i.e., as integer numbers instead of bit vectors) greater than a given constant bound. The pattern appears to occur when compiling several Rust projects (it seems to originate from the `smallvec` crate but I have not checked this further). Unless `c1` is `0`, we can transform this pattern into `x > c2/c1` with all operations working on unsigned integers. Due to undefined behavior when an element of a non-splat vector is `0`, the transform is only implemented for scalars and splat vectors. Alive proof: https://alive2.llvm.org/ce/z/LawTkm Closes #142674