This PR implements tracing of with contexts with TorchFunction modes which have the default enter/exit behavior (ie pushing/popping the mode)
Typically the bytecode for a context manager looks like this during a graph break:
1. graph call
2. enter context
3. unsupported code
4. exit context
5. resume call
resume fn structure:
1. enter context
2. jump
...
3. exit context
The issue with torch function modes is that side effects will replay any mutations to the torch function stack performed during tracing. So, we do not need to enter and exit around the unsupported code in the original function (doing so would result in a duplicate torch function mode entry during execution of the unsupported code), and we don't need to enter again in the resume function (the mode that was pushed from the side effects bytecode would still be on the stack).
So for torch function modes the structure of our output code is this:
1. graph call
2. mutate tf mode stack to replay mutations
4. unsupported code
5. on exception restore stack
6. resume function
Then our resume fn looks like this:
1. no-op enter torch function mode
2. jump
3. exit tf mode
To implement the no-op enter of the torch function mode I added torch function mode in polyfill which no-op enters, but normally exits. This is needed because we still want to trace the with context in the resume function, and exit properly (the exit instructions will still be in the function, so we need to generate instructions to set up the context).
Separately from the bytecode, dynamo also tracks contexts on the block stack, which is how the SETUP_* instructions are implemented. Naturally at a graph break, we exit these block stacks to properly reset the contexts entirely, so that we can re-enter around the unsupported code soundly. However once again, in the torch function mode case, in the event of a graph we do not want to perform any exit side effects because we want to preserve the state of the mode stack as is so that we will properly update the stack with bytecode mentioned in the first section. If we exited here, dynamo would pop the mode off of the symbolic stack, and not update the true python torch function mode stack with the suffix bytecode. All in all, for torch function modes we enter exactly once, update the global torch function mode stack with side effects bytecode, re-read this stack when compiling the resume function, and exit exactly once in the resume function. This matches the semantics of eager exactly.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/135422
Approved by: https://github.com/williamwen42
ghstack dependencies: #134732, #133137, #135443, #135444
This PR implements tracing of with contexts with TorchFunction modes which have the default enter/exit behavior (ie pushing/popping the mode)
Typically the bytecode for a context manager looks like this during a graph break:
1. graph call
2. enter context
3. unsupported code
4. exit context
5. resume call
resume fn structure:
1. enter context
2. jump
...
3. exit context
The issue with torch function modes is that side effects will replay any mutations to the torch function stack performed during tracing. So, we do not need to enter and exit around the unsupported code in the original function (doing so would result in a duplicate torch function mode entry during execution of the unsupported code), and we don't need to enter again in the resume function (the mode that was pushed from the side effects bytecode would still be on the stack).
So for torch function modes the structure of our output code is this:
1. graph call
2. mutate tf mode stack to replay mutations
4. unsupported code
5. on exception restore stack
6. resume function
Then our resume fn looks like this:
1. no-op enter torch function mode
2. jump
3. exit tf mode
To implement the no-op enter of the torch function mode I added torch function mode in polyfill which no-op enters, but normally exits. This is needed because we still want to trace the with context in the resume function, and exit properly (the exit instructions will still be in the function, so we need to generate instructions to set up the context).
Separately from the bytecode, dynamo also tracks contexts on the block stack, which is how the SETUP_* instructions are implemented. Naturally at a graph break, we exit these block stacks to properly reset the contexts entirely, so that we can re-enter around the unsupported code soundly. However once again, in the torch function mode case, in the event of a graph we do not want to perform any exit side effects because we want to preserve the state of the mode stack as is so that we will properly update the stack with bytecode mentioned in the first section. If we exited here, dynamo would pop the mode off of the symbolic stack, and not update the true python torch function mode stack with the suffix bytecode. All in all, for torch function modes we enter exactly once, update the global torch function mode stack with side effects bytecode, re-read this stack when compiling the resume function, and exit exactly once in the resume function. This matches the semantics of eager exactly.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/135422
Approved by: https://github.com/williamwen42
ghstack dependencies: #134732, #133137, #135443, #135444
This PR implements tracing of with contexts with TorchFunction modes which have the default enter/exit behavior (ie pushing/popping the mode)
Typically the bytecode for a context manager looks like this during a graph break:
1. graph call
2. enter context
3. unsupported code
4. exit context
5. resume call
resume fn structure:
1. enter context
2. jump
...
3. exit context
The issue with torch function modes is that side effects will replay any mutations to the torch function stack performed during tracing. So, we do not need to enter and exit around the unsupported code in the original function (doing so would result in a duplicate torch function mode entry during execution of the unsupported code), and we don't need to enter again in the resume function (the mode that was pushed from the side effects bytecode would still be on the stack).
So for torch function modes the structure of our output code is this:
1. graph call
2. mutate tf mode stack to replay mutations
4. unsupported code
5. on exception restore stack
6. resume function
Then our resume fn looks like this:
1. no-op enter torch function mode
2. jump
3. exit tf mode
To implement the no-op enter of the torch function mode I added torch function mode in polyfill which no-op enters, but normally exits. This is needed because we still want to trace the with context in the resume function, and exit properly (the exit instructions will still be in the function, so we need to generate instructions to set up the context).
Separately from the bytecode, dynamo also tracks contexts on the block stack, which is how the SETUP_* instructions are implemented. Naturally at a graph break, we exit these block stacks to properly reset the contexts entirely, so that we can re-enter around the unsupported code soundly. However once again, in the torch function mode case, in the event of a graph we do not want to perform any exit side effects because we want to preserve the state of the mode stack as is so that we will properly update the stack with bytecode mentioned in the first section. If we exited here, dynamo would pop the mode off of the symbolic stack, and not update the true python torch function mode stack with the suffix bytecode. All in all, for torch function modes we enter exactly once, update the global torch function mode stack with side effects bytecode, re-read this stack when compiling the resume function, and exit exactly once in the resume function. This matches the semantics of eager exactly.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/135422
Approved by: https://github.com/williamwen42
ghstack dependencies: #134732, #133137, #135443, #135444
Significant bytecode generation API change!
The new suggested convention to generating bytecode to call a function is now to wrap instructions that push a callable to the stack with `add_push_null`, then that callable is called with `create_call_function` with `push_null=False` (see diff for examples).
In Python 3.13, NULL is now expected to be pushed after the callable. In <=3.12, the NULL was pushed before the callable. This change abstracts away the exact placement of the NULL, but the developer must be aware that a NULL may be needed when codegen'ing a callable.
This abstraction also reduces the need for the `push_null=True` option in `create_call_function`, which removes the need to rotate a NULL to the right place on the stack with a sequence of `SWAP` instructions.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/129172
Approved by: https://github.com/jansel
Fix https://github.com/pytorch/pytorch/issues/124900.
When we reconstruct `ContextWrappingVariables`s, we only reconstruct the context class, not the object. Normally, contexts are active (via `with ctx:`) and we initialize the context object in the resume function. But for the case of inactive contexts (contexts declared ahead of time before the `with` block), we do not reconstruct them properly in the optimized bytecode or resume function. So this PR adds initialization for inactive contexts in the resume function.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/125203
Approved by: https://github.com/jansel
resume_in_* code objects show up in user backtraces when failures occur
in code that has been Dynamo processed. It is obvious to me, a PT2
developer, that these are generated by PT2, but it is NOT obvious to a
non-core dev that this is happened. Add an extra torch_dynamo
breadcrumb to help get people to the right place.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118201
Approved by: https://github.com/albanD
Since Python 3.11 bytecode contains endline and column information, for each bytecode, we attribute the source code corresponding to the bytecode in a more accurate way. For example, we can highlight a function call in a series of nested function calls, or highlight a function call spanning multiple lines.
Sample:
```python
import torch
import torch._dynamo
from functorch.experimental.control_flow import cond
def h(x):
return x * 5
def true_fn(x):
return x * 2
def false_fn(x):
return x * 3
def f(pred, x):
x = h(
h(h(x))
)
x = x[1:][:2]
torch._dynamo.graph_break()
x = cond(pred, true_fn, false_fn, [x])
opt_f = torch.compile(f, backend="eager")
opt_f(torch.tensor(True), torch.randn(3, 3, 3, 3))
```
Output:
```
$ TORCH_LOGS="trace_call" python playground9.py
TRACE inlined call h from f /scratch/williamwen/work/pytorch/playground9.py:16
h(h(x))
~^^^
TRACE FX call mul from h /scratch/williamwen/work/pytorch/playground9.py:6 (inline depth: 1)
return x * 5
~~^~~
TRACE inlined call h from f /scratch/williamwen/work/pytorch/playground9.py:16
h(h(x))
~^^^^^^
TRACE FX call mul_1 from h /scratch/williamwen/work/pytorch/playground9.py:6 (inline depth: 1)
return x * 5
~~^~~
TRACE inlined call h from f /scratch/williamwen/work/pytorch/playground9.py:15
x = h(
~^
h(h(x))
^^^^^^^
)
^
TRACE FX call mul_2 from h /scratch/williamwen/work/pytorch/playground9.py:6 (inline depth: 1)
return x * 5
~~^~~
TRACE FX call getitem from f /scratch/williamwen/work/pytorch/playground9.py:18
x = x[1:][:2]
~^^^^
TRACE FX call getitem_1 from f /scratch/williamwen/work/pytorch/playground9.py:18
x = x[1:][:2]
~~~~~^^^^
TRACE inlined call true_fn from <resume in f> /scratch/williamwen/work/pytorch/playground9.py:20
x = cond(pred, true_fn, false_fn, [x])
~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TRACE FX call mul from true_fn /scratch/williamwen/work/pytorch/playground9.py:9 (inline depth: 1)
return x * 2
~~^~~
TRACE inlined call false_fn from <resume in f> /scratch/williamwen/work/pytorch/playground9.py:20
x = cond(pred, true_fn, false_fn, [x])
~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TRACE FX call mul from false_fn /scratch/williamwen/work/pytorch/playground9.py:12 (inline depth: 1)
return x * 3
~~^~~
TRACE FX call cond from <resume in f> /scratch/williamwen/work/pytorch/playground9.py:20
x = cond(pred, true_fn, false_fn, [x])
~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/104676
Approved by: https://github.com/ezyang
- Replace `for inst in instructions[0:targe.offset//2]: inst.starts_line = None`, with the one that that iterates over all instructions until `inst.offset == target.offset` condition is met, this way making it uniform across Python bytecode dialects (Python-3.11+ bytecode size is variable, while bytecode size is fixed for older Pythons)
- Speedup target_index search by replacing `[i for i in instructions if i.offset == offset][0]` with `next(i for i in instructions if i.offset == offset)`, which aborts the evaluation after condition met for the first time, according to:
```python
In [1]: lst=list(range(10000))
In [2]: %time [i for i in lst if i == 10]
CPU times: user 144 µs, sys: 23 µs, total: 167 µs
Wall time: 168 µs
Out[2]: [10]
In [3]: %time next(i for i in lst if i == 10)
CPU times: user 6 µs, sys: 0 ns, total: 6 µs
Wall time: 9.06 µs
Out[3]: 10
```
- Fix small typo
- use `is_py311_plus` variable rather than checking `sys.version_info`
<!--
copilot:poem
-->
### <samp>🤖 Generated by Copilot at 6cd7f27</samp>
> _We fix the typos in our code of doom_
> _We remove the warnings that obscure our vision_
> _We refactor the `generate` function for the dynamo_
> _We resume the execution with precision_
Fixes https://github.com/pytorch/pytorch/issues/103355
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103525
Approved by: https://github.com/Skylion007, https://github.com/williamwen42
Summary of changes:
- Add CPython exceptiontable parsing/assembling functions in torch/_dynamo/bytecode_transformation.py, based on https://github.com/python/cpython/blob/3.11/Objects/exception_handling_notes.txt.
- Add optional `exn_tab_entry` field to dynamo `Instruction`s in torch/_dynamo/bytecode_transformation.py in order to virtualize exception table entries (start, end, target instructions).
- Add checks guarding against duplicate instructions in dynamo, so that jump/exceptiontable targets are unambiguous. See `get_indexof` in torch/_dynamo/bytecode_analysis.py. Ensure that bytecode generation throughout dynamo does not generate duplicate instructions.
- Allow dynamo bytecode generation logic to generate nested exception table entries for developer convenience. CPython expects entries to not overlap, so we flatten nested entries during assembly in torch/_dynamo/bytecode_transformation.py:compute_exception_table.
- Simulate the block stack in torch/_dynamo/symbolic_convert.py. CPython removed the block stack in 3.11, but dynamo needs it in order to keep track of active contexts. So we simulate the block stack as before by looking at exceptiontable entries in order to determine the current blocks.
- Update context codegen in torch/_dynamo/resume_execution.py. The `SETUP_FINALLY` bytecode, which conveniently had a jump target to the finally block, was removed in 3.11, so we need to keep track of the jump target of the finally block using exceptiontables. Generating resume functions is more difficult since the original exceptiontable entries pointing to old cleanup code need to be modified to point to new cleanup code.
- Fix a push_null bug in torch/_dynamo/variables/functions.py introduced by https://github.com/pytorch/pytorch/pull/98699
Pull Request resolved: https://github.com/pytorch/pytorch/pull/96511
Approved by: https://github.com/jansel, https://github.com/yanboliang, https://github.com/albanD
Fixes https://github.com/pytorch/pytorch/issues/93890
We do the following:
1. fix __init__constructor for `AutocastModeVariable` with exisiting `mode` while copying
2. `resume_execution` is made aware of constant args (`target_values`), by storing said args in `ReenterWith`. To propagate between subgraphs (in straightline code), we also store the constant args in the downstream's `code_options["co_consts"]` if not already.
---
Future work:
1. handle instantiating context manager in non-inlineable functions. Simultaneously fix nested grad mode bug.
2. generalize to general `ContextManager`s
3. generalize to variable arguments passed to context manager, with guards around the variable.
---
Actually, if we look at the repro: 74592a43d0/test/dynamo/test_repros.py (L1249), we can see that the method in this PR doesn't work for graph breaks in function calls, in particular, in function calls that don't get inlined.
Why inlining functions with graph breaks is hard:
- When we handle graph breaks, we create a new code object for the remainder of the code. It's hard to imagine doing this when you are inside a function, then we need a frame stack. And we just want to deal with the current frame as a sequence of straight line codes.
Why propagating context manager information is hard:
- If we do not inline the function, the frame does not contain any information about the parent `block_stack` or `co_consts`. So we cannot store it on local objects like the eval frame. It has to be a global object in the output_graph.
---
Anyway, I'm starting to see clearly that dynamo must indeed be optimized for torch use-case. Supporting more general cases tends to run into endless corner-cases and caveats.
One direction that I see as viable to handle function calls which have graph breaks and `has_tensor_in_frame` is stick with not inlining them, while installing a global `ContextManagerManager`, similar to the `CleanupManager` (which cleans up global variables). We can know which context managers are active at any given point, so that we can install their setup/teardown code on those functions and their fragments.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94137
Approved by: https://github.com/yanboliang
