llvm-project

b75530ff - [LoopInterchange] Consider forward/backward dependency in vectorize heuristic (#133672)

[LoopInterchange] Consider forward/backward dependency in vectorize heuristic (#133672) The vectorization heuristic of LoopInterchange attempts to move a vectorizable loop to the innermost position. Before this patch, a loop was deemed vectorizable if there are no loop-carried dependencies induced by the loop. This patch extends the vectorization heuristic by introducing the concept of forward and backward dependencies, inspired by LoopAccessAnalysis. Specifically, an additional element is appended to each direction vector to indicate whether it represents a forward dependency (`<`) or not (`*`). Among these, only the forward dependencies (i.e., those whose last element is `<`) affect the vectorization heuristic. Accordingly, the check is conservative, and dependencies are considered forward only when this can be proven. Currently, we only support perfectly nested loops whose body consists of a single basic block. For other cases, dependencies are pessimistically treated as non-forward.