fix[venom]: make truthy or rule wrap-aware

[banteg]

What I did

Fixes #5072.

The algebraic optimizer's truthy-position or rule treated an unwrapped literal equal to 2**256 — which is zero as an EVM word — as nonzero, folding or 2**256, %x in an assert position to constant 1 instead of depending on %x.

How I did it

One-line fix in _rule_or: the raw check ops[0].value != 0 becomes wrap-aware not lit_eq(ops[0], 0), consistent with the x | 0 -> x rule directly below it which already uses lit_eq. Audited the rest of the file for the same raw-.value truthiness pattern; this was the only instance.

How to verify it

test_or_truthy_unwrapped_zero_literal parses the issue reproducer, runs AlgebraicOptimizationPass, and asserts the or reduces to %x rather than constant 1. Fails on master.

Commit message

the truthy-position `or` rule checked raw literal truthiness
(`ops[0].value != 0`), so an unwrapped literal equal to 2**256 --
which wraps to zero as an EVM word -- was treated as nonzero and the
expression was folded to constant 1, even though it is equivalent to
`or 0, %x` and must depend on %x.

make the check wrap-aware via the existing `lit_eq` helper, consistent
with the `x | 0 -> x` rule below it.

Description for the changelog

Fix: Venom algebraic optimizer no longer folds or with an unwrapped zero literal (e.g. 2**256) to constant true in truthy positions.

Cute Animal Picture

[charles-cooper]

are there other bugs of this class in algebraic opts?

[banteg]

Audited the rest of algebraic_optimization.py for the same raw-literal vs wrapped-EVM-word class.

Found one adjacent issue in signextend: the byte index operand is also an EVM word, so 2**256 must be treated as byte index 0, not as >= 31. I pushed follow-up commit 49cf212b4 to make the direct signextend(n, x) no-op rule and the nested signextend(n, signextend(m, x)) rule use wrapped literal values, with regressions for both cases.

The remaining raw .value uses in the pass are either immediately normalized with wrap256/lit_eq, or are in the power-of-two strength reduction path after wrapped-zero/one cases have already been handled.

Checked with:

uv run --python 3.12 -m pytest tests/unit/compiler/venom/test_algebraic_binopt.py tests/unit/compiler/venom/test_algebraic_optimizer.py
uv run --python 3.12 ruff check vyper/venom/passes/algebraic_optimization.py tests/unit/compiler/venom/test_algebraic_binopt.py

[banteg]

I did a quick sweep of the rest of AlgebraicOptimizationPass for the same raw-literal/wrap class. I do not see another confirmed correctness bug.

The remaining direct literal reads are in the power-of-two strength-reduction probe for mul/div/mod. The wrap-zero aliases are already caught by the preceding lit_eq(..., 0) rule; non-canonical aliases like a literal that wraps to 2 but is not syntactically a power of two would just miss the strength reduction rather than produce a wrong rewrite. The comparator and signextend paths now go through wrap256/lit_word_value where the literal value affects correctness.

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.84%. Comparing base (242a4fa) to head (49cf212).
⚠️ Report is 15 commits behind head on master.

Files with missing lines	Patch %	Lines
vyper/venom/passes/algebraic_optimization.py	90.90%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5082      +/-   ##
==========================================
- Coverage   92.93%   92.84%   -0.10%     
==========================================
  Files         188      191       +3     
  Lines       27840    29385    +1545     
  Branches     4831     5151     +320     
==========================================
+ Hits        25874    27282    +1408     
- Misses       1315     1411      +96     
- Partials      651      692      +41     

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[github-actions]

Gas Changes

No changes detected.

Summary

• Total tests measured: 815
• Changed: 0
• Regressions (gas up): 0
• Improvements (gas down): 0
• New tests: 0
• Deleted tests: 0
• Newly failing: 0
• Newly passing: 0

[github-actions]

📊 Bytecode Size Changes (venom)

No changes detected.

Full bytecode sizes

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