Return is control flow, but TIRx currently represents it as an
Evaluate-wrapped intrinsic call. This prevents return values from
participating naturally in statement traversal and requires special-case
handling across the pipeline.
This change introduces a reflected tirx.Return statement carrying an
Expr, wires it through TVMScript, statement visitors and mutators,
lowering, storage planning, and C/LLVM code generation, and removes the
legacy tirx.ret and T.ret surfaces.
Tianqi Chen
9bfefb7e4b