Jevin Jiang 839ce9a11d [Pallas TPU] Refactor ref indexers to transforms and support ref bitcast.
This cl refactors Pallas memref indexers to transforms which can support different ref transforms: indexing, bitcast (added in this cl), reshape (to be added) and others. Like indexer, user can apply multiple transforms to same memref, eg:
```
ref.bitcast(type1).at[slice1].bitcast(type2).bitcast(type3).at[slice2]...
```

Jaxpr Preview (apply multiple transforms to same ref):
```
{ lambda ; a:MemRef<None>{int32[16,256]} b:MemRef<None>{int32[8,128]}. let
    c:i32[8,128] <- a[:8,:][bitcast(int16[16,256])][bitcast(float16[16,256])][:,:128][bitcast(int32[8,128])][:,:]
    b[:,:] <- c
  in () }
```

Tested:
* DMA with bitcasted ref
* Load from bitcasted ref
* Store to bitcasted ref
* Multiple transforms
* Interpret Mode for ref transforms (updated discharge rules)
PiperOrigin-RevId: 674961388
2024-09-15 17:53:29 -07:00
..
2024-06-26 16:10:18 -04:00