jinhongyii opened a new pull request, #19669:
URL: https://github.com/apache/tvm/pull/19669
## Summary
`CanonicalSimplifier::Impl::VisitExpr_(LTNode)` Case 2 rewrites
S + xn < 0 ⇔ S/d + xn // d < 0 where d = gcd(scales)
The Case 1 derivation only works when `xn ≥ 0`. With `scale = -1` the
equivalence becomes `≤` rather than `<`, and the rewrite silently strengthens
the predicate by dropping the boundary `S/d == xn // d`.
After CSE/inlining, a comparison such as `2*(tx%4) < 16*warp + (tx%32)//4`
(where `row` and `col` are independent projections of the same lane id) reaches
canonical_simplify with the divided projection on the LHS (scale = -1), and
Case 2 folds it to a plain `0 < warp_id` — zeroing every thread that should
have written `val` in warp 0. The same path also folds other configurations
(e.g. `0 < (tx%32) - 8*warp`) all the way to `False`.
The fix gates Case 2 with `extra->args[0]->scale == 1`. The original target
shape (`yn % m` with positive scale and `lower_factor=1`, plus the `scale = +1
/ lower_factor > 1` generalization) is unchanged; truly-always-true comparisons
still fold to `True`.
## Test plan
- New regression test `test_simplify_le_negative_scale_extra` in
`tests/python/arith/test_arith_canonical_simplify.py` — asserts on simplified
`PrimExpr`, no GPU required; pre-fix fails, post-fix passes. It also pins the
buggy `scale = -1` shapes to their unsimplified form, confirms the `scale = +1`
Case 2 path still optimizes, and re-asserts the truly-always-true variant still
folds to `True`.
- Existing `test_simplify_le` (the original Case 2 target with `scale = +1`)
still passes.
- `tests/python/arith/test_arith_canonical_simplify.py` — 16 passed.
- Full `tests/python/arith/` — 932 passed (1 pre-existing flaky random-seed
failure in `test_arith_solve_linear_equations.py` unrelated to this change,
passes on rerun).
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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