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Fix LLONG_MIN errors in torch.jit.script #153793

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Fix LLONG_MIN errors in torch.jit.script #153793

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xuantengh
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Convert ast.UnaryOp to a ast.Constant node if the operand is a numeric ast.Constant.

Fixes #153722

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pytorch-bot bot commented May 18, 2025 •
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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/153793

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@pytorchbot label "topic: not user facing"

@pytorch-bot pytorch-bot bot added the topic: not user facing topic category label May 18, 2025
@HDCharles HDCharles requested a review from huydhn May 20, 2025 17:50
@HDCharles HDCharles added the triaged This issue has been looked at a team member, and triaged and prioritized into an appropriate module label May 20, 2025
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@ezyang @malfet
Could you help get this PR reviewed?

@ezyang ezyang self-requested a review June 6, 2025 01:47
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ezyang commented Jun 6, 2025

I am a little reluctant to merge this because TS is in maintenance mode, and I cannot tell that this is obviously safe. Here is what O3 thinks, and I think the added suggested tests are enough due diligence:

Below is a “safety audit” style review of the UnaryOpCombiner pass and the new test. I’ve focused on semantic-level corner cases rather than style/nit comments.

1. What the patch actually changes

  • Before: -9223372036854775808 is parsed as

    UnaryOp(op=USub, operand=Constant(value=9223372036854775808)).

    When TorchScript later tried to down-cast that positive literal to int64, it overflowed.

  • After: The new UnaryOpCombiner folds the unary operator into the literal early, producing a single Constant(value=-9223372036854775808).

    That value now fits in signed 64 bits, so the cast succeeds and the new test passes.

2. Edge-case behaviours worth checking

Family of cases Why it matters Expected outcome after patch
Nested unary ops (--1, ~~~0) Visit order & idempotency Should fully fold, e.g. --1 → 1
Positive no-op (+1, +True) UAdd path must exist; idempotent Stays same value
not on constants (not 0, not True) Changes type (int → bool) Produces literal True/False
bool vs int64 (-True, ~True) bool is a subclass of int; JIT tensor type inference may differ Should still infer int64, but verify
Float −0.0 (-0.0) Sign-bit preservation Constant(value=-0.0) (print may show -0.0)
Complex literals (-(1+2j)) Operator in UNARY_OPS supports complex Should fold to (-1-2j)
Values outside 64-bit (-(2**100)) We now create negative huge int; casting still fails → consistent error? Should raise same overflow error as positive huge int
Future Python AST nodes New unary op class ⇒ KeyError Guard with if type(node.op) not in UNARY_OPS

5. Overall risk assessment

  • 📈 Value: Fixes a real int64 down-cast overflow with minimal code.

  • ⚠️ Main risk: Silent type changes from not or ~ on constants.  These are legal Python semantics, but TorchScript users sometimes rely on bool→int autoconversion.

  • 🛡 Mitigation:

    • Add the corner-case test matrix above.

    • Guard the UNARY_OPS lookup.

    • Document in UnaryOpCombiner’s docstring that it pre-evaluates unary ops on literals and may change the AST shape accordingly.


With those guards in place, the pass looks safe to merge.

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github-actions bot commented Aug 5, 2025

Looks like this PR hasn't been updated in a while so we're going to go ahead and mark this as Stale.
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@huydhn huydhn Awaiting requested review from huydhn

@ezyang ezyang Awaiting requested review from ezyang

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JIT Script doesn't handle LLONG_MIN correctly
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@xuantengh @BartlomiejStemborowski @ezyang @pytorchbot @HDCharles