WarpExecuteOnLane0Op::verify() called getTerminator() which performed an
unconditional cast<gpu::YieldOp> on the block's last operation. When the
op body was written with a different terminator (e.g. affine.yield), the
cast asserted immediately instead of emitting a verifier diagnostic.
Fix by using dyn_cast in verify() before calling getTerminator(), and
emitting a proper error message when the terminator is not gpu.yield.
Add a regression test to invalid.mlir.
Fixes#181450
1909e43a4a