[Pytorch Backend delegation] Add api for backend lowering to query debug (#55462)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55462
handles and symbolicate exception callstack thrown from backend.
Objective of this diff is to achieve improve error reporting when
exceptions are raised from lowered backend. We would effectively like to
get the same model level stack trace that you would get without having
lowered some module to backend.
For example:
```
class AA(nn.Module):
def forward(self, x, y):
return x + y
class A(nn.Module):
def __init__(...):
self.AA0 = AA()
def forward(self, x, y):
return self.AA0.forward(x, y) + 3
class B(nn.Module):
def forward(self, x):
return x + 2
class C(nn.Module):
def __init__(...):
self.A0 = A()
self.B0 = B()
def forward(self, x, y):
return self.A0.forward(x, y) + self.B0.forward(x)
```
If the we then do C().forward(torch.rand((2,3)), torch.rand(14,2))) we
will likely see error stack like:
```
C++ exception with description "The following operation failed in the TorchScript interpreter.
Traceback of TorchScript (most recent call last):
File "<string>", line 3, in forward
def forward(self, x, y):
return self.A0.forward(x, y) + self.B0.forward(x)
~~~~~~~~~~~~~~~ <--- HERE
File "<string>", line 3, in forward
def forward(self, x, y):
return self.AA0.forward(x, y) + 3
~~~~~~~~~~~~~~~~ <--- HERE
File "<string>", line 3, in forward
def forward(self, x, y):
return x + y
~~~~~ <--- HERE
```
We would like to see the same error stack if we lowered C.A0 to some
backend.
With this diff we get something like:
```
Module hierarchy:top(C).A0(backend_with_compiler_demoLoweredModule).AA0(AA)
Traceback of TorchScript (most recent call last):
File "<string>", line 3, in FunctionName_UNKNOWN
def forward(self, x, y):
return self.A0.forward(x, y) + self.B0.forward(x)
~~~~~~~~~~~~~~~ <--- HERE
File "<string>", line 5, in FunctionName_UNKNOWN
typed_inputs: List[Any] = [x, y, ]
if self.__backend.is_available() :
_0, = self.__backend.execute(self.__handles["forward"], typed_inputs)
~~~~~~~~~~~~~~~~~~~~~~ <--- HERE
assert isinstance(_0, Tensor)
return _0
File "<string>", line 3, in FunctionName_UNKNOWN
def forward(self, x, y):
return self.AA0.forward(x, y) + 3
~~~~~~~~~~~~~~~~ <--- HERE
File "<string>", line 3, in FunctionName_UNKNOWN
def forward(self, x, y):
return x + y
~~~~~ <--- HERE
```
This is achieved in 3 parts:
Part 1:
A. BackendDebugInfoRecorder:
During backend lowering, in `to_backend`, before calling the preprocess
function corresponding to the backend. This will facilitate recording of
debug info (such as source range + inlined callstack) for the lowered module.
B. Instantiate WithBackendDebugInfoRecorder with BackendDebugInfoRecorder.
This initializes thread local pointer to BackendDebugInfoRecorder.
C. generate_debug_handles:
In preprocess function, the backend will call generate_debug_handles
for each method being lowered separately. generate_debug_handles
takes `Graph` of the method being lowered and returns a map
of Node*-to-debug_handles. Backend is responsible for storing debug
handles appropriately so as to raise exception (and later profiling)
using debug handles when the exception being raised corresponds to
particular Node that was lowered.
Inside generate_debug_handles, we will query the current
BackendDebugHandleInfoRecorder, that is issuing debug handles. This debug
handle manager will issue debug handles as well as record
debug_handles-to-<source range, inlined callstack> map.
D. Back in `to_backend`, once the preprocess function is has finished
lowering the module, we will call `stopRecord` on
BackendDebugInfoRecorder. This will return the debug info map. This
debug info is then stored inside the lowered module.
Part 2:
Serialization:
During serialization for bytecode (lite interpreter), we will do two
things:
1. Extract all the source ranges that are contained inside
debug_handles-to-<source range, inlined callstack> map for lowered
module. This will be source range corresponding to debug handles,
including what is there is inlined callstack. Since we replaced original
module with lowered module, we wont be serializing code for the original
module and thus no source range. That is why the source range will have
to be stored separately. We will lump all the source ranges for all the
lowered modules in one single debug_pkl file.
2. Then we will serialize debug_handles-to-<source range, inlined
callstack> map.
Now during deserialization we will be able to reconstruct
debug_handles-to-<source range, inlined callstack> map. Given all
debug_handles are unique we would not need any module information.
Test Plan:
Tests are added in test_backend.cpp
Tests are added in test_backend.cpp
Imported from OSS
Differential Revision:
D27621330
D27621330
Reviewed By: raziel
Pulled By: kimishpatel
fbshipit-source-id: 0650ec68cda0df0a945864658cab226a97ba1890
pytorch
d6d726f7 - [Pytorch Backend delegation] Add api for backend lowering to query debug (#55462)
