Launching the Debugger

1. In Remix, deploy a contract or execute a transaction.

2. Go to the transaction list (in the Deploy & Run tab) and click the “bug” icon next to the transaction you’re interested in. This will launch the Debugger.

Using the Debugger

Once you’re inside the debugger:

1. Navigation: Use the step controls to navigate through each operation of your transaction. You can step over, into, or out of functions and jump to a particular step.

2. Details Panel: This panel will show opcode details, the current execution step, and other relevant details.

3. Solidity Locals: Displays the local Solidity variables and their current values.

4. State: Shows the contract’s state changes. It’s a great place to identify unexpected changes, which may cause higher gas fees.

5. Call Stack: Illustrates the current function call stack. Useful for understanding the current execution context.

6. Storage Changes: Highlights changes to storage during execution. Useful for identifying potential areas of gas optimization.

Profiling with Debugger for Gas Insights

The debugger isn’t just for fixing bugs; it’s also an excellent tool for profiling your contract’s gas usage. Here’s how you can get the most out of it:

1. Identify High Gas Steps: As you step through your code, monitor the gas usage at each step. High gas steps could be optimization targets.

2. Monitor Storage Actions: Excessive storage changes, especially ones that don’t delete, could be gas guzzlers.

3. Function Calls: External function calls, especially to other contracts, can be expensive. Ensure they’re necessary.

Practice Example

Let’s use the Remix Debugger with a simple contract:

Solidity
pragma solidity ^0.8.9;

contract GasProfiler {
    uint256 public count;

    function setCount(uint256 _count) public {
        for (uint256 i = 0; i < _count; i++) {
            count += i;
        }
    }
}

1. Deploy and interact with the contract in Remix.

2. Use the debugger on the setCount function and identify the gas-intensive operations. Here, the loop operation will consume more gas as _count increases.

Conclusion

Understanding and making the most out of Remix Debugger is a skill that will not only aid in diagnosing issues but also in refining your contract to be gas-efficient. By stepping through your code, you can spot inefficiencies that might not be apparent at a higher level.