Crash when checkpointing an empty call graph
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- C++
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Description
Running with master (d65bd5e) on Python 3.5.2 on a CPU, this crashes:
import dynet as dy
model = dy.Model()
x = model.add_parameters((10,10))
dy.cg_checkpoint()
However, this succeeds:
import dynet as dy
model = dy.Model()
x = model.add_parameters((10,10))
y = x*x
dy.cg_checkpoint()
I think it might have something to do with _get_checkpoint calling mark, which has this line, and the last part evaluates to -1 when there are no nodes:
cg->incremental_forward({cg, (VariableIndex)(cg->nodes.size() - 1)});
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Research direction
Run the two Python reproductions to confirm that dy.cg_checkpoint() crashes only with an empty call graph. Then inspect _get_checkpoint and mark in dynet/devices.cc, especially the incremental_forward call linked in the issue. Done means checkpointing the empty graph succeeds without regressing the nonempty-graph case.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp, python
- Domain
- machine-learning
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100