[scan] support gen_schema for scan #158864
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This was referenced Jul 22, 2025
🔗 Helpful Links🧪 See artifacts and rendered test results at hud.pytorch.org/pr/158864
Note: Links to docs will display an error until the docs builds have been completed. ✅ No FailuresAs of commit a9f4e34 with merge base 96bd33b ( This comment was automatically generated by Dr. CI and updates every 15 minutes. |
This was referenced Jul 22, 2025
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[ghstack-poisoned]
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example: ```python def combine_fn(init, x): ``` If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn. If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet. [ghstack-poisoned]
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example: ```python def combine_fn(init, x): ``` If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn. If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet. [ghstack-poisoned]
This was referenced Jul 24, 2025
zou3519
approved these changes
Jul 31, 2025
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example: ```python def combine_fn(init, x): ``` If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn. If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet. [ghstack-poisoned]
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example: ```python def combine_fn(init, x): ``` If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn. If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet. [ghstack-poisoned]
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example: ```python def combine_fn(init, x): ``` If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn. If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet. [ghstack-poisoned]
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Starting merge as part of PR stack under #158883 |
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Starting merge as part of PR stack under #158883 |
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Starting merge as part of PR stack under #158883 |
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Starting merge as part of PR stack under #158883 |
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example: ```python def combine_fn(init, x): ``` If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn. If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet. [ghstack-poisoned]
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Starting merge as part of PR stack under #158883 |
can-gaa-hou
pushed a commit
to can-gaa-hou/pytorch
that referenced
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Aug 22, 2025
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example: ```python def combine_fn(init, x): ``` If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn. If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet. Pull Request resolved: pytorch#158864 Approved by: https://github.com/zou3519 ghstack dependencies: pytorch#154193, pytorch#158965, pytorch#158863
can-gaa-hou
pushed a commit
to can-gaa-hou/pytorch
that referenced
this pull request
Aug 22, 2025
…58883) In-place mutation may create inter-loop dependency that breaks the parallelism we have for associative_scan so we ban input mutations. Pull Request resolved: pytorch#158883 Approved by: https://github.com/zou3519 ghstack dependencies: pytorch#154193, pytorch#158965, pytorch#158863, pytorch#158864
markc-614
pushed a commit
to markc-614/pytorch
that referenced
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Sep 17, 2025
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example: ```python def combine_fn(init, x): ``` If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn. If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet. Pull Request resolved: pytorch#158864 Approved by: https://github.com/zou3519 ghstack dependencies: pytorch#154193, pytorch#158965, pytorch#158863
markc-614
pushed a commit
to markc-614/pytorch
that referenced
this pull request
Sep 17, 2025
…58883) In-place mutation may create inter-loop dependency that breaks the parallelism we have for associative_scan so we ban input mutations. Pull Request resolved: pytorch#158883 Approved by: https://github.com/zou3519 ghstack dependencies: pytorch#154193, pytorch#158965, pytorch#158863, pytorch#158864
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Stack from ghstack (oldest at bottom):
We don't want to allow scan's combine_fn to mutate its inputs. The semantic of the mutation can be confusing. For example:
If combine_fn mutates init, only first iteration mutates init, the rest of the iterations mutates the previous carry, which is an intermediate result. This is kind of a weird semantic because the only observable mutation is for init, which can be done outside of the combine_fn.
If combine_fn mutates x, where x is a slice of scanned inputs (i.e. xs), this pattern is more meaningful but we've not seen any use case yet.