Signed arithmetic overflow: document the compiler contract before changing optimization
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Separate arithmetic requirements from GCC overflow flags when a release build behaves differently from a debug build.
What it is
GCC documents -fwrapv as requesting wrapping behavior for signed addition, subtraction and multiplication, while -ftrapv requests traps for those operations. The options interact, and their order and active state matter. These are explicit compiler contracts with stated scope, not interchangeable ways to make every arithmetic operation safe. GCC optimization options
Why it matters
An agent investigating a release-only bug may disable optimization and stop. That establishes an environmental difference, but leaves the intended arithmetic unspecified. For counts, lengths and offsets, decide whether an out-of-range result should be rejected, saturated, widened or wrapped before choosing an implementation.
How to apply
- Capture the actual compile flags for the failing translation unit, including inherited build settings. Record the compiler and target rather than relying on the build-profile name.
- Write the valid operand ranges and intended result policy beside the calculation. For an allocation size, include intermediate calculations rather than considering only the final destination type.
- Construct proposed boundary cases just inside and outside the permitted range. Keep expected results independent of whatever the current executable happens to print.
- Prefer a checked arithmetic operation or a mathematically justified range check when rejection is required. If wrapping is deliberately part of the contract, state which operations and compilation units rely on it.
- Compare debug and release configurations using the same fixtures, then inspect relevant diagnostics. Retain the smallest example showing why the chosen contract is necessary.
Pitfalls
Do not assume a wider destination rescues an intermediate calculation performed in a narrower type. A flag documented for addition, subtraction and multiplication is not a blanket promise about division, shifts or pointers. Avoid silently changing flags across the whole project to fix one local operation. The proposed checks are an investigation plan; no compiler experiment or passing boundary test is claimed here.
範囲と根拠
Original synthesis from the cited primary documentation, with proposed diagnostic and verification steps. No benchmark, experiment or field result is claimed; unreviewed AI-assisted contribution.
知識の基準日：2026-09-22。状態：unreviewed（レビュー記録なし） — 編集するとレビュー状態はリセットされます。本文は未検証の参考情報として扱い、出典を確認してください。
出典
- GCC optimization options — 2026-09-22 確認：到達可能、引用箇所あり
帰属とライセンス
- Account External coding curation authors (57eb56c9)
- Written with Codex, an AI coding agent, at the site operator's request; original synthesis, sources credited separately.
最新の変更： New English original; AI-assisted and unreviewed. Proposed checks have not been executed for this article.
オリジナルの投稿： CC BY 4.0. リンク先の出典はそれぞれの権利を保持します。