make @non_differentiable use identical pullbacks when possible
#1147
| Job | Run time |
|---|---|
| 24m 55s | |
| 1m 55s | |
| 41s | |
| 2m 39s | |
| 2m 28s | |
| 2m 12s | |
| 2m 9s | |
| 5m 17s | |
| 4m 9s | |
| 57s | |
| 3m 9s | |
| 2m 3s | |
| 8m 29s | |
| 1h 1m 3s |