Fix: DDE removing read from access_set in read/write nodes #1964
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## Description For this bug to show, we need two separate states with a transient produced in one and subsequently read and written (but not read again). It is important that `StateFusion` isn't able to merge these two state. I've put a dummy if/else in the middle. Before DDE this might look like  where `tmp_computed` is transient and `tmp` is a given variable. DDE will now go and see that `tmp_computed` can be removed as an output of the `read_write` tasklet. The currently faulty update of `access_set` will remove `tmp_computed` from the list of reads in `block` state. This will then propagate (badly) up to the `start` state where `tmp_computed` is marked as never read again, removing the whole tasklet, leaving the `block` state to read an uninitialized `tmp_computed` (if we were to codegen).  ### Repro ```python import dace import os # Create an empty SDFG sdfg = dace.SDFG(os.path.basename(__file__).removesuffix(".py").replace("-", "_")) sdfg.add_scalar("tmp", dace.float32) sdfg.add_scalar("tmp_computed", dace.float32, transient=True) start_state = sdfg.add_state("start", is_start_block=True) read_tmp = start_state.add_read("tmp") write_computed = start_state.add_write("tmp_computed") # upstream tasklet that writes a transient (to be read in a separate state) write = start_state.add_tasklet("write", {"IN_tmp"}, {"OUT_computed"}, "OUT_computed = IN_tmp * 2 + 1") start_state.add_memlet_path(read_tmp, write, dst_conn="IN_tmp", memlet=dace.Memlet(data="tmp")) start_state.add_memlet_path(write, write_computed, src_conn="OUT_computed", memlet=dace.Memlet(data="tmp_computed")) # Add a condition to avoid fusing next_state and start_state separate guard = sdfg.add_state_after(start_state, "guard_state") true_state = sdfg.add_state("true_state") false_state = sdfg.add_state("false_state") fs_read = false_state.add_read("tmp") fs_write = false_state.add_write("tmp") fs_tasklet = false_state.add_tasklet("abs", {"IN_tmp"}, {"OUT_tmp"}, "OUT_tmp = -IN_tmp") false_state.add_memlet_path(fs_read, fs_tasklet, dst_conn="IN_tmp", memlet=dace.Memlet("tmp")) false_state.add_memlet_path(fs_tasklet, fs_write, src_conn="OUT_tmp", memlet=dace.Memlet("tmp")) merge = sdfg.add_state("merge_state") sdfg.add_edge(guard, true_state, dace.InterstateEdge("tmp >= 0")) sdfg.add_edge(guard, false_state, dace.InterstateEdge("tmp < 0")) sdfg.add_edge(true_state, merge, dace.InterstateEdge()) sdfg.add_edge(false_state, merge, dace.InterstateEdge()) next_state = sdfg.add_state_after(merge) write_computed = next_state.add_write("tmp_computed") read_computed = next_state.add_read("tmp_computed") write_tmp = next_state.add_write("tmp") # downstream tasklet that reads _and_ writes a transient consume = next_state.add_tasklet("read_write", {"IN_computed"}, {"OUT_tmp", "OUT_computed"}, "OUT_computed = 2 * IN_computed\nOUT_tmp = OUT_computed + IN_computed") next_state.add_memlet_path(read_computed, consume, dst_conn="IN_computed", memlet=dace.Memlet(data="tmp_computed")) next_state.add_memlet_path(consume, write_tmp, src_conn="OUT_tmp", memlet=dace.Memlet(data="tmp")) next_state.add_memlet_path(consume, write_computed, src_conn="OUT_computed", memlet=dace.Memlet(data="tmp_computed")) sdfg.validate() sdfg.simplify(verbose=True, validate=True) assert len(list(filter(lambda node: isinstance(node, dace.sdfg.nodes.Tasklet), sdfg.start_block.nodes()))) == 1, "write tasklet in start_block is gone" ``` ### Finishing this PR I'll need help to evaluate whether or not the proposed solution is a good one. Questions that I have: - Is this the right place to fix it? - Should we manually change `access_sets` or would it be simpler/more reliable to redo the analysis step? - The repro case translates to a unit test. Is it a good one or should I e.g. call DDE directly and write assertions for the output of the pass? --------- Co-authored-by: Roman Cattaneo <1116746+romanc@users.noreply.github.com>
romanc
reviewed
Mar 6, 2025
Co-authored-by: Roman Cattaneo <romanc@users.noreply.github.com>
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Cherry picking fix to the data flow elimination path from V1/maintenance. Original PR: #1955