make @non_differentiable use identical pullbacks when possible
#1151
| Job | Run time |
|---|---|
| 25m 29s | |
| 1m 56s | |
| 44s | |
| 2m 29s | |
| 2m 28s | |
| 2m 11s | |
| 2m 7s | |
| 5m 8s | |
| 4m 3s | |
| 1m 0s | |
| 3m 11s | |
| 2m 4s | |
| 8m 38s | |
| 1h 1m 28s |