llvm-project

c92b580d - [mlir][ArmSME] Remove `ConvertIllegalShapeCastOpsToTransposes` (#139706)

[mlir][ArmSME] Remove `ConvertIllegalShapeCastOpsToTransposes` (#139706) As a follow-up to PR #135841 (see discussion for background), this patch removes the `ConvertIllegalShapeCastOpsToTransposes` pattern from the SME legalization pass. This change unblocks folding for ShapeCastOp involving scalable vectors. Originally, the `ConvertIllegalShapeCastOpsToTransposes` pattern was introduced to rewrite certain `vector.shape_cast` ops that could not be lowered otherwise. Based on local end-to-end testing, this workaround is no longer required, and the pattern can now be safely removed. This patch also removes a special case from `ShapeCastOp::fold`, simplifying the fold logic. As a side effect of removing `ConvertIllegalShapeCastOpsToTransposes`, we lose the mechanism that enabled lowering of certain ops like: ```mlir %res = vector.transfer_read %mem[%a, %b] (...) : memref<?x?xf32>, vector<[4]x1xf32> ``` Previously, such cases were handled by: * Rewriting a nearby `vector.shape_cast` to a `vector.transpose` (via `ConvertIllegalShapeCastOpsToTransposes`) * Then lowering the result with `LiftIllegalVectorTransposeToMemory`. This patch introduces a new dedicated pattern, `LowerColumnTransferReadToLoops`, that directly handles illegal `vector.transfer_read` ops involving leading scalable dimensions.