In general a JAX value might correspond to multiple HLO values, which is why the HLO lowering represents each value as a tuple of zero or more ir.Values. However, the common case is that there is exactly one value, and almost all such lists are singletons.
To reduce the number of singleton list and tuple objects allocated during MLIR lowering, instead represent singleton values as unwrapped ir.Values, and only use a tuple if there is not exactly one ir.Value backing a JAX value.
This allows lowering of threefry2x32 for GPU even on a machine without GPUs.
For the next 3 weeks, we only use the new custom call implementation if
we are not in "export" mode, and if we use a new jaxlib.
PiperOrigin-RevId: 647657084
The motivation for doing this is 2-fold:
1) This will help with deprecating and eventually deleting `jax.xla_computation` which allows for cross backend lowering.
2) Allow for cross-backend and multi-backend lowering via jax AOT APIs which will help cleanup some hacks implemented for `jax.export`.
Note that this is only available by `.trace.lower(lowering_platforms=('tpu',))`. You cannot use `.lower` to do cross-lowering. We can introduce top-level APIs in the future to allow for composable aot apis to make this easier if `.trace(*args).lower(lowering_platforms)` is cumbersome to write.
Designed with @froystig!
PiperOrigin-RevId: 644087787
We take the opportunity of a new jax.export package to rename some
of the API entry points:
* `Exported.uses_shape_polymorphism` is renamed to `Exported.uses_global_constants`
because this is more accurate. The dimension variables are global
constants, but so is the platform index. And we need to run
global constant propagation and shape refinement for all of these.
* We rename "serialization version" with "calling convention version".
Hence we now have `Exported.calling_convention_version`,
and the configuration flag is renamed from `--jax-serialization-version`
to `--jax-export-calling-convention-version`. Also,
`jax.export.minimum_supported_serialization_version` is now
`jax.export.minimum_supported_calling_convention_version`.
* We rename `lowering_platforms` to `platforms` both as a field
of `Exported` and as the kwarg to `export.export`.
* We rename `jax.export.default_lowering_platform` to `jax.export.default_export_version`.
Previously we declared Exported.in_shardings to be
a sequence of `core.AbstractValue`, but in reality we only
support `core.ShapedArray`. We change the type declaration and
this allowed us to clean up some `# type: ignore"
The functionality comes from the jax.experimental.export
module, which will be deprecated.
The following APIs are introduced:
```
from jax import export
def f(...): ...
ex: export.Exported = export.export(jax.jit(f))(*args, **kwargs)
blob: bytearray = ex.serialize()
rehydrated: export.Export = export.deserialize(blob)
def caller(...):
... rehydrated.call(*args, **kwargs)
```
Module documentation will follow shortly.
There are no changes for now in the jax.experimental.export
APIs.
Most of the changes in this PR are in tests due to some differences
in the new jax.export APIs compared to jax.experimental.export:
* Instead of `jax.experimental.export.call(exp)` we now write
`exp.call`
* The `jax.experimental.export.export` allowed the function
argument to be any Python callable and it would wrap it with
a `jax.jit`. This is not supported anymore by export, and instead
the user must use `jax.jit`.
This is part of the work to move the export APIs out
of jax.experimental. For now, the way to use this
implementation is still through `jax.experimental.export`.
Had to add a few "#type ignore" to the _export.py because
previously the file was exempt from internal pytype.
Will try to fix these in a later PR.
PiperOrigin-RevId: 641688200
