make @non_differentiable use identical pullbacks when possible
#1149
| Job | Run time |
|---|---|
| 25m 37s | |
| 2m 0s | |
| 41s | |
| 2m 27s | |
| 2m 27s | |
| 2m 15s | |
| 2m 12s | |
| 5m 8s | |
| 4m 2s | |
| 1m 1s | |
| 3m 5s | |
| 2m 7s | |
| 8m 29s | |
| 1h 1m 31s |