[Fix] Scope deferred_runtime_asserts per piecewise sub-graph to prevent NameError#27
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cennn merged 1 commit intoApr 27, 2026
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…nt NameError After piecewise splitting, sub-graphs share the same ShapeEnv whose deferred_runtime_asserts may reference backed SymInts (e.g. s90) that only exist as placeholders in another sub-graph. Inductor blindly emits these as Python runtime assertions, causing NameError at runtime. Add _scope_deferred_runtime_asserts context manager that temporarily narrows deferred_runtime_asserts to only reachable backed symbols before each standalone_compile call, then restores the original dict afterwards. Includes pytest that reproduces the bug (patch fix away → NameError) and verifies the fix (with fix → passes).
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🗂️ PR Category
Problem
After piecewise splitting, each sub-graph is compiled via
standalone_compileindependently but shares the sameShapeEnv. When unbacked SymInts (frommark_unbacked) createEqconstraints linking multiple backed SymInts(e.g.
Eq(u0+u1+u2, s77)andEq(u0+u1+u2, s90)), Inductor'sGraphLoweringblindly copies the entiredeferred_runtime_assertsdict and emits each entry as a Python runtime assertion. A sub-graph that only hass90in its placeholders still inheritsEq(u0+u1+u2, s77), generatingif not (u0+u1+u2 == s77):wheres77is undefined →NameError.Fix
Add
_scope_deferred_runtime_assertscontext manager inpiecewise_compiler.py.Before each
standalone_compilecall, it:example_inputsdeferred_runtime_assertsto only those whose backed symbols are all reachableOnly applied when
dynamic_shapes="from_tracing_context"(Inductor-specific).Test
test_piecewise_deferred_assert_scope.py:test_without_fix_raises_nameerror: patches fix away → confirmsNameErrortest_with_fix_passes: runs with fix → passes with two different shapes