perf: optimize ReentrancyGuardTransient with pre-computed BooleanSlot

[borj404]

Description

Eliminates redundant type casting in ReentrancyGuardTransient by pre-computing the BooleanSlot wrapper at compile-time.

Edit: Updated to support the new nonReentrantView modifier introduced in the latest version.

Current implementation

Performs asBoolean() → BooleanSlot.wrap() three times per nonReentrant execution.

Optimization

Pre-computed constant:

TransientSlot.BooleanSlot private constant REENTRANCY_SLOT =
    TransientSlot.BooleanSlot.wrap(REENTRANCY_GUARD_STORAGE);

Gas savings

19 gas per nonReentrant call (verified via test suite).

Method	Original gas	Optimized gas	Savings	Improvement
callback()	44,007	43,988	19 gas	0.04%
guardedCheckEntered()	21,952	21,933	19 gas	0.09%

Eliminates 30 gas in wrapping operations, reduced to 19 gas net due to function call overhead from the refactored architecture.
Deployment overhead: 1,728 gas (amortized after ~91 transactions).

Testing

• All existing tests pass unmodified.
• Full benchmark: https://github.com/borj404/openzeppelin-transient-reentrancy-gas-optimization/tree/optimize/reentrancy-guard-transient

Impact

• Zero security trade-offs.
• Full backward compatibility.
• Supports both nonReentrant and nonReentrantView modifiers.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2f1f537

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
openzeppelin-solidity	Patch

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[coderabbitai]

Walkthrough

Adds a pre-computed TransientSlot.BooleanSlot constant (REENTRANCY_SLOT) in ReentrancyGuardTransient.sol to wrap REENTRANCY_GUARD_STORAGE. Replaces repeated _reentrancyGuardStorageSlot().asBoolean().tload()/tstore(...) calls with REENTRANCY_SLOT.tload()/tstore(...) in _nonReentrantBefore, _nonReentrantAfter, and _reentrancyGuardEntered. Updates related inline comments. Retains _reentrancyGuardStorageSlot() unchanged. Functional behavior remains unchanged. Also adds a changeset entry marking an openzeppelin-solidity patch release documenting this optimization.

Possibly related issues

• Gas optimization: Cache BooleanSlot in ReentrancyGuardTransient #5837: Implements the same pre-computed TransientSlot.BooleanSlot approach in ReentrancyGuardTransient.sol for the same gas-saving objective.

Possibly related PRs

• Add _reentrancyGuardStorageSlot()  #5892: Modifies the same ReentrancyGuardTransient internal slot access to use a pre-computed wrapper across _nonReentrantBefore/_nonReentrantAfter/_reentrancyGuardEntered.

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Pre-merge checks

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title Check	✅ Passed	The current title succinctly and accurately identifies the primary change—precomputing a BooleanSlot to optimize ReentrancyGuardTransient—and clearly communicates the performance focus and affected contract to reviewers. It is concise, specific, and free of irrelevant details or emojis. This makes it appropriate for commit history and team review.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.
Description Check	✅ Passed	The pull request description directly corresponds to the changeset: it explains precomputing the TransientSlot.BooleanSlot wrapper in ReentrancyGuardTransient, includes the implementation snippet, reports measured gas savings and deployment overhead, and notes that tests pass, so it is related and informative for this lenient check.

[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

.changeset/thick-goats-travel.md (1)

5-5: Minor discrepancy in gas savings documentation.

The changeset mentions "30 gas per call" while the PR objectives specify "19 gas saved per nonReentrant call." Consider aligning these numbers for consistency across documentation.

-Optimize ReentrancyGuardTransient by pre-computing BooleanSlot wrapper to save 30 gas per call
+Optimize ReentrancyGuardTransient by pre-computing BooleanSlot wrapper to save 19 gas per call

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• contracts/utils/ReentrancyGuardTransient.sol (2 hunks)

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🔇 Additional comments (5)

contracts/utils/ReentrancyGuardTransient.sol (5)

22-30: Excellent gas optimization with clear documentation.

The pre-computed BooleanSlot constant is a smart optimization that eliminates redundant type casting operations. The comprehensive comment clearly explains the rationale and quantifies the gas savings, making it easy for future maintainers to understand the purpose.

---

70-70: LGTM! Clean replacement of redundant operations.

The direct usage of REENTRANCY_SLOT.tstore(true) eliminates the need for the previous _reentrancyGuardStorageSlot().asBoolean().tstore(true) pattern, reducing gas consumption while maintaining identical functionality.

Also applies to: 74-74

---

78-78: LGTM! Consistent optimization applied.

The direct usage of REENTRANCY_SLOT.tstore(false) follows the same optimization pattern as in _nonReentrantBefore(), maintaining consistency across the codebase.

---

86-86: LGTM! Optimization maintains function semantics.

The direct usage of REENTRANCY_SLOT.tload() eliminates the redundant _reentrancyGuardStorageSlot().asBoolean().tload() pattern while preserving the exact same return value and behavior.

---

89-91: Good design choice preserving backward compatibility.

Maintaining the _reentrancyGuardStorageSlot() function unchanged ensures that any external contracts or libraries that depend on this function for storage slot access continue to work without modification. This demonstrates excellent backward compatibility considerations.

[Amxx]

We need to account for _reentrancyGuardStorageSlot being virtual.

[Amxx]

This PR uses a constant object that correspond to the default location (REENTRANCY_GUARD_STORAGE). This means it does not consider the possibility that the value may be changed by overriding _reentrancyGuardStorageSlot.

Doing that change would be breaking, and would provide no alternative workflow to override the slot used.

[borj404]

For full context on this optimization’s evolution:

This PR was originally opened against the version that repeatedly called .asBoolean() on the REENTRANCY_GUARD_STORAGE constant, resulting in redundant wrap operations at runtime. Pre-computing the BooleanSlot wrapper at compile time eliminated those repeated conversions, saving 30 gas per nonReentrant call.

After the first refactor (introduction of nonReentrantView and code restructuring), the same optimization still applied cleanly, though gas savings dropped to 19 gas per call due to reduced redundancy.

The recent introduction of the virtual _reentrancyGuardStorageSlot() rendered the optimization incompatible.

Under this new architecture, my proposed version hardcodes the slot to the default value, silently breaking any contract that overrides it. I agree that’s an unacceptable trade-off for a utility designed to be extended.

While the gas savings were meaningful in earlier versions, I fully respect the decision to prioritize correctness and composability over micro-optimizations, especially in foundational code.

Made sense when the slot was static. Doesn’t anymore. Appreciate the review.