torch-mlir/frontends/pytorch/README.md

59 lines
2.6 KiB
Markdown
Raw Normal View History

# NPComp - PyTorch frontend integration
This directory contains optional components for interfacing PyTorch to NPComp.
Integration is targeted at multiple levels:
* Via program capture with a ATen pseudo-device.
* Via IR-level integration with PyTorch (via tracing or scripting interfaces).
* Interfaces to facilitate checking against reference implementations and
verification.
In all situations, the target dialects are maintained in the outer project,
along with their lowerings to common intermediate dialects and backends. This
directory should be purely about interfacing with the PyTorch/LibTorch
components for extracting and executing programs.
Add pytorch interface to ATen Dialect (#30) This patch adds a pytorch interface to npcomp. This interface is modeled after pytorch_xla and exposes the MLIR-based flow as a virtual device (similar to a gpu device or the xla backend). Usage is intended to be something like: dev = torch_mlir.mlir_device() t0 = torch.randn((4,4), device=dev) t1 = torch.randn((4,4), device=dev) t2 = t0 + t1 t2_mlir = torch_mlir.get_mlir( t2 ) t2_cpu = t2.to('cpu') In this case t2_cpu would contain the result of the computation, and t2_mlir contains the mlir description of the computation. Note that this also properly returns backward paths synthesized by pytorch. There are several parts of this: 1) A tensor type (implemented by tensor.* and tensor_impl.*) 2) The device modeling (aten_mlir_bridge.*, aten_mlir_device.*, aten_mlir_type*) 3) a temporary IR (implemented by ir.cpp) There is also a reference lowering directly from the ATen dialect to C function calls consisting of two parts: 1) The driver that uses the IR to generate MLIR, run Passes and compile the result using mlir::ExecutionEngine (implemented by jit.cpp and mlir_gen.cpp) 2) A runtime library implemented by lib/aten_ops.cpp. Most of the operations are implemented by callbacks into the torch C++ libraries. Some aspects of this are known to be less than optimal, in particular: 1) There's some function definitions that don't live in the file corresponding to their declaration. 2) More aspects of this (e.g. the IR) seem like they should be automatically generated. 3) It's unclear to me how much of the 'IR' is actually necessary, or whether MLIR could be created on the fly. Note that this code is licensed in a way similar to pytorch, with the intention that eventually (when npcomp reaches some maturity) it should be pushed there. (see frontends/pytorch/LICENSE) The code is also structured much closer to the pytorch coding style than the LLVM coding style.
2020-08-22 02:22:47 +08:00
The code in this directory is intended to integrate tightly with pytorch, and
follows the code style for pytorch. See the [overall documentation for
frontends](../README.md) for further details about code layout and integration
philosophy. In particular, this directory exists to provide a working
frontend to an MLIR based pytorch compilation flow and is not intended to be
contributed to the LLVM monorepo. If the project is successful, it makes more
sense to either break it out as an independent project that depends on
LLVM/MLIR/npcomp or contribute it upstream to PyTorch. However, as it will be
quite some time before the components are in a state to support such a
dependency, it is being carried in-tree in the interim.
2021-03-31 02:33:18 +08:00
### Program capture with a ATen dispatch capture.
Add pytorch interface to ATen Dialect (#30) This patch adds a pytorch interface to npcomp. This interface is modeled after pytorch_xla and exposes the MLIR-based flow as a virtual device (similar to a gpu device or the xla backend). Usage is intended to be something like: dev = torch_mlir.mlir_device() t0 = torch.randn((4,4), device=dev) t1 = torch.randn((4,4), device=dev) t2 = t0 + t1 t2_mlir = torch_mlir.get_mlir( t2 ) t2_cpu = t2.to('cpu') In this case t2_cpu would contain the result of the computation, and t2_mlir contains the mlir description of the computation. Note that this also properly returns backward paths synthesized by pytorch. There are several parts of this: 1) A tensor type (implemented by tensor.* and tensor_impl.*) 2) The device modeling (aten_mlir_bridge.*, aten_mlir_device.*, aten_mlir_type*) 3) a temporary IR (implemented by ir.cpp) There is also a reference lowering directly from the ATen dialect to C function calls consisting of two parts: 1) The driver that uses the IR to generate MLIR, run Passes and compile the result using mlir::ExecutionEngine (implemented by jit.cpp and mlir_gen.cpp) 2) A runtime library implemented by lib/aten_ops.cpp. Most of the operations are implemented by callbacks into the torch C++ libraries. Some aspects of this are known to be less than optimal, in particular: 1) There's some function definitions that don't live in the file corresponding to their declaration. 2) More aspects of this (e.g. the IR) seem like they should be automatically generated. 3) It's unclear to me how much of the 'IR' is actually necessary, or whether MLIR could be created on the fly. Note that this code is licensed in a way similar to pytorch, with the intention that eventually (when npcomp reaches some maturity) it should be pushed there. (see frontends/pytorch/LICENSE) The code is also structured much closer to the pytorch coding style than the LLVM coding style.
2020-08-22 02:22:47 +08:00
Integration with a pseudo-device is typified by code like the following:
```
2021-03-31 02:33:18 +08:00
import torch
import torch_mlir
lhs = torch.rand(2, 3)
rhs = torch.rand(3, 4)
mb = torch_mlir.ModuleBuilder()
with mb.capture_function("mm", [lhs, rhs]) as f:
result = torch.mm(lhs, rhs)
f.returns([result])
mb.module.operation.print()
Add pytorch interface to ATen Dialect (#30) This patch adds a pytorch interface to npcomp. This interface is modeled after pytorch_xla and exposes the MLIR-based flow as a virtual device (similar to a gpu device or the xla backend). Usage is intended to be something like: dev = torch_mlir.mlir_device() t0 = torch.randn((4,4), device=dev) t1 = torch.randn((4,4), device=dev) t2 = t0 + t1 t2_mlir = torch_mlir.get_mlir( t2 ) t2_cpu = t2.to('cpu') In this case t2_cpu would contain the result of the computation, and t2_mlir contains the mlir description of the computation. Note that this also properly returns backward paths synthesized by pytorch. There are several parts of this: 1) A tensor type (implemented by tensor.* and tensor_impl.*) 2) The device modeling (aten_mlir_bridge.*, aten_mlir_device.*, aten_mlir_type*) 3) a temporary IR (implemented by ir.cpp) There is also a reference lowering directly from the ATen dialect to C function calls consisting of two parts: 1) The driver that uses the IR to generate MLIR, run Passes and compile the result using mlir::ExecutionEngine (implemented by jit.cpp and mlir_gen.cpp) 2) A runtime library implemented by lib/aten_ops.cpp. Most of the operations are implemented by callbacks into the torch C++ libraries. Some aspects of this are known to be less than optimal, in particular: 1) There's some function definitions that don't live in the file corresponding to their declaration. 2) More aspects of this (e.g. the IR) seem like they should be automatically generated. 3) It's unclear to me how much of the 'IR' is actually necessary, or whether MLIR could be created on the fly. Note that this code is licensed in a way similar to pytorch, with the intention that eventually (when npcomp reaches some maturity) it should be pushed there. (see frontends/pytorch/LICENSE) The code is also structured much closer to the pytorch coding style than the LLVM coding style.
2020-08-22 02:22:47 +08:00
```
2021-03-31 02:33:18 +08:00
All operations that happen under the `mb.capture_function` context manager are
intercepted via PyTorch's
[dispatcher](http://blog.ezyang.com/2020/09/lets-talk-about-the-pytorch-dispatcher/),
and an IR graph is constructed into the module held by the ModuleBuilder.
Add pytorch interface to ATen Dialect (#30) This patch adds a pytorch interface to npcomp. This interface is modeled after pytorch_xla and exposes the MLIR-based flow as a virtual device (similar to a gpu device or the xla backend). Usage is intended to be something like: dev = torch_mlir.mlir_device() t0 = torch.randn((4,4), device=dev) t1 = torch.randn((4,4), device=dev) t2 = t0 + t1 t2_mlir = torch_mlir.get_mlir( t2 ) t2_cpu = t2.to('cpu') In this case t2_cpu would contain the result of the computation, and t2_mlir contains the mlir description of the computation. Note that this also properly returns backward paths synthesized by pytorch. There are several parts of this: 1) A tensor type (implemented by tensor.* and tensor_impl.*) 2) The device modeling (aten_mlir_bridge.*, aten_mlir_device.*, aten_mlir_type*) 3) a temporary IR (implemented by ir.cpp) There is also a reference lowering directly from the ATen dialect to C function calls consisting of two parts: 1) The driver that uses the IR to generate MLIR, run Passes and compile the result using mlir::ExecutionEngine (implemented by jit.cpp and mlir_gen.cpp) 2) A runtime library implemented by lib/aten_ops.cpp. Most of the operations are implemented by callbacks into the torch C++ libraries. Some aspects of this are known to be less than optimal, in particular: 1) There's some function definitions that don't live in the file corresponding to their declaration. 2) More aspects of this (e.g. the IR) seem like they should be automatically generated. 3) It's unclear to me how much of the 'IR' is actually necessary, or whether MLIR could be created on the fly. Note that this code is licensed in a way similar to pytorch, with the intention that eventually (when npcomp reaches some maturity) it should be pushed there. (see frontends/pytorch/LICENSE) The code is also structured much closer to the pytorch coding style than the LLVM coding style.
2020-08-22 02:22:47 +08:00
This technique has several advantages and disadvantages. For training use
cases, this technique generates a backward path automatically using the same
method that pytorch natively uses. The resulting graph also tends to be
simpler, since it will not reflect conditionals in the original python
code. Lastly, it is natural if MLIR is being used as a frontend target for an
actual device of some sort. In this case, the MLIR could go through a
device-specific lowering path and the resulting code run on a device.
2021-03-31 02:33:18 +08:00
The implementation of this technique is largely modeled after `pytorch/xla`.