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@IllIllI000
Last active June 24, 2023 13:48
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STACK VARIABLES DO NOT SAVE GAS BY SKIPPING INITIALIZATION TO ZERO

If you've found this page via one of my old gas reports, please see this link

SetVsDefault_s.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.13; // optimize 200

/**
 * @title SetVsDefault
 * @author IllIllI
 */
contract SetVsDefault {
    function test(uint256 x) external pure returns(uint256) {
        for (uint256 i = 0; i < 10; ++i) {
	    x += 2;
	}
	return x;
    }
}

SetVsDefault_d.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.13; // optimize 200

/**
 * @title SetVsDefault
 * @author IllIllI
 */
contract SetVsDefault {
    function test(uint256 x) external pure returns(uint256) {
        for (uint256 i; i < 10; ++i) {
	    x += 2;
	}
	return x;
    }
}

Diff

diff --git a/SetVsDefault_s.sol b/SetVsDefault_d.sol
index 7594b22..541d4cd 100644
--- a/SetVsDefault_s.sol
+++ b/SetVsDefault_d.sol
@@ -7,7 +7,7 @@ pragma solidity 0.8.13; // optimize 200
  */
 contract SetVsDefault {
     function test(uint256 x) external pure returns(uint256) {
-        for (uint256 i = 0; i < 10; ++i) {
+        for (uint256 i; i < 10; ++i) {
 	    x += 2;
 	}
 	return x;

Compiled binary

$ solc SetVsDefault_s.sol --bin --optimize --optimize-runs 200 | egrep "^60[0-9]+"
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

$ solc SetVsDefault_d.sol --bin --optimize --optimize-runs 200 | egrep "^60[0-9]+"
608060405234801561001057600080fd5b50610108806100206000396000f3fe6080604052348015600f57600080fd5b506004361060285760003560e01c806329e99f0714602d575b600080fd5b603c60383660046079565b604e565b60405190815260200160405180910390f35b6000805b600a811015607257606360028460a7565b9250606c8160bc565b90506052565b5090919050565b600060208284031215608a57600080fd5b5035919050565b634e487b7160e01b600052601160045260246000fd5b6000821982111560b75760b76091565b500190565b60006001820160cb5760cb6091565b506001019056fea2646970667358221220420fe424b02a4807f8f2f77e369fe5a3f85008d62b7cc05b8d3ee79b9e55334464736f6c634300080d0033

Opcodes

no bytecode differences

@0xean
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0xean commented Sep 22, 2022

Adding some more info here for the next person that takes a look. (make sure optimizer is enabled). I wanted to confirm this held for a non pure function. It does.

// SPDX-License-Identifier: MIT
pragma solidity 0.8.17; 


contract SetVsDefault1 {
    uint256 randomVar;
    

    function test(uint256 x) external returns(uint256) {
        for (uint256 i = 0; i < 10; ++i) {
	        x = x + 2;
	    }
        randomVar = x;
	    return x;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity 0.8.17; 


contract SetVsDefault2 {
    uint256 randomVar;
    

    function test(uint256 x) external returns(uint256) {
        for (uint256 i; i < 10; ++i) {
	        x = x + 2;
	    }
        randomVar = x;
	    return x;
    }
}

Screen Shot 2022-09-22 at 8 34 20 AM

@aviksaikat007
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noob question. How to get that beautiful output?

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