make @non_differentiable use identical pullbacks when possible (#679)
#1152
| Job | Run time |
|---|---|
| 25m 31s | |
| 2m 1s | |
| 37s | |
| 2m 26s | |
| 2m 32s | |
| 2m 33s | |
| 2m 10s | |
| 4m 55s | |
| 4m 2s | |
| 57s | |
| 3m 2s | |
| 2m 5s | |
| 8m 23s | |
| 1h 1m 14s |