We can use `__index__` to do this conversion because that will trigger a
guard on data dependent SymInt if the tensor is a fake tensor, but if
we fetch item directly and put it in the Scalar, we may still be able to
make it work out.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/117454
Approved by: https://github.com/yanboliang
ghstack dependencies: #117451, #117452
Adds `SingletonSymNodeImpl` (alternatively, `SkolemSymNodeImpl`). This is a int-like object that only allows the`eq` operation; any other operation produces an error.
The main complexity is that we require operations that dispatch to SymNode must take and return SymNodes, but when performing operations involving `SingletonSymNodeImpl`, operations involving SymNode can return non-SymNode bools. For more discussion see [here](https://docs.google.com/document/d/18iqMdnHlUnvoTz4BveBbyWFi_tCRmFoqMFdBHKmCm_k/edit)
- Introduce `ConstantSymNodeImpl` a generalization of `LargeNegativeIntSymNodeImpl` and replace usage of `LargeNegativeIntSymNodeImpl` in SymInt.
- Also use ConstantSymNodeImpl to enable SymBool to store its data on a SymNode. Remove the assumption that if SymBool holds a non-null SymNode, it must be symbolic.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107089
Approved by: https://github.com/ezyang
ghstack dependencies: #107839
This PR stops `SymNode` from mutating (i.e. simplifying) its expression. Instead, the
simplification (without mutation) is deferred to the `SymNode.maybe_as_int` method.
```python
- FakeTensor(size=(s0,), ...)
- FakeTensor(size=(s1, s2, s3), ...)
- Eq(s0, s1 + s2 + s3)
- FakeTensor(size=(s0,), ...)
- FakeTensor(size=(s1, s2, s3), ...)
```
In summary, this PR:
- Replaces `SymNode._expr` by `SymNode.expr`, removing the old property function
- This makes it so `SymNode` instances never update their expression
- Creates `SymNode.simplified_expr()` method for actually calling `ShapeEnv.replace` on
its expression. Note that this doesn't updates `SymNode.expr`
- Changes how `tensor.size()` gets converted to its Python `torch.Size` type
- Instead of calling `SymInt::maybe_as_int()` method, we create a new
`SymInt::is_symbolic()` method for checking whether it is actually a symbolic value
- This is needed so that when we call `tensor.size()` in the Python side, the returned
sequence is faithful to the actual data, instead of possibly simplifying it and
returning an integer
- 2 files needs this modification:
- _torch/csrc/Size.cpp_: for handling `torch.Tensor.size` Python calls
- _torch/csrc/utils/pybind.cpp_: for handling `symint.cast()` C++ calls
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107492
Approved by: https://github.com/ezyang
ghstack dependencies: #107523
The strategy is that we will heap allocate a LargeNegativeIntSymNodeImpl whenever we have a large negative int, so that we can keep the old `is_symbolic` test (now called `is_heap_allocated`) on SymInt. Whenever we need to do something with these ints, though, we convert them back into a plain `int64_t` (and then, e.g., wrap it in whatever user specificed SymNodeImpl they need.) We cannot wrap directly in the user specified SymNodeImpl as we generally do not know what the "tracing context" is from C++. We expect large negative ints to be rare, so we don't apply optimizations like singleton-ifying INT_MIN. Here's the order to review:
* c10/core/SymInt.h and cpp
* `is_symbolic` renamed to `is_heap_allocated` as I needed to audit all use sites: the old `is_symbolic` test would return true for large negative int, but it would be wrong to then try to dispatch on the LargeNegativeIntSymNodeImpl which supports very few operations. In this file, I had to update expect_int,
* If you pass in a large negative integer, we instead heap allocate it in `promote_to_negative`. The function is written in a funny way to keep compact constructor code for SymInt (the heap allocation happens out of line)
* clone is now moved out-of-line
* New method maybe_as_int which will give you a constant int if it is possible, either because it's stored inline or in LargeNegativeIntSymNodeImpl. This is the preferred replacement for previous use of is_symbolic() and then as_int_unchecked().
* Rename toSymNodeImpl to toSymNode, which is more correct (since it returns a SymNode)
* Complete rewrite of `normalize_symints.cpp` to use new `maybe_as_int`. Cannot easily use the old code structure, so it's now done doing a macro and typing out each case manually (it's actually not that bad.)
* Reimplementations of all the unary operators by hand to use `maybe_as_int`, relatively simple.
* c10/core/LargeNegativeIntSymNodeImpl.h - Just stores a int64_t value, but it has to be big and negative. Most methods are not implemented, since we will rewrap the large negative int in the real SymNodeImpl subclass before doing operations with it
* The rest of the files are just rewriting code to use `maybe_as_int`. There is a nontrivial comment in c10/core/SymIntArrayRef.h
Very minor test adjustment in c10/test/core/SymInt_test.cpp . Plan to exercise this properly in next PR.
Companion XLA PR: https://github.com/pytorch/xla/pull/4882
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99157
Approved by: https://github.com/albanD
The big idea is to add `create_unbacked_symfloat` and `create_unbacked_symint` to ShapeEnv, allowing you to allocate symbolic floats/ints corresponding to data you don't know about at compile time. Then, instead of immediately erroring out when you try to call local_scalar_dense on a FakeTensor, we instead create a fresh symint/symfloat and return that.
There a bunch of odds and ends that need to be handled:
* A number of `numel` calls converted to `sym_numel`
* When we finally return from item(), we need to ensure we actually produce a SymInt/SymFloat when appropriate. The previous binding code assumed that you would have to get a normal Python item. I add a pybind11 binding for Scalar (to PyObject only) and refactor the code to use that. There is some trickiness where you are NOT allowed to go through c10::SymInt if there isn't actually any SymInt involved. See comment.
* One of our unit tests tripped an implicit data dependent access which occurs when you pass a Tensor as an argument to a sizes parameter. This is also converted to support symbolic shapes
* We now support tracking bare SymInt/SymFloat returns in proxy tensor mode (this was already in symbolic-shapes branch)
* Whenever we allocate an unbacked symint, we record the stack trace it was allocated at. These get printed when you attempt data dependent access on the symint (e.g., you try to guard on it)
* Subtlety: unbacked symints are not necessarily > 1. I added a test for this.
These unbacked symints are not very useful right now as you will almost always immediately raise an error later when you try to guard on them. The next logical step is adding an assertion refinement system that lets ShapeEnv learn facts about unbacked symints so it can do a better job eliding guards that are unnecessary.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90624
Approved by: https://github.com/Skylion007, https://github.com/voznesenskym
