plus-equal-cost-more-for-state-variables

README.md

@@ -133,6 +133,7 @@ use-prefix-increment-not-postfix | The prefix increment expression is cheaper in
 use-short-revert-string | Shortening revert strings to fit in 32 bytes will decrease gas costs for deployment and gas costs when the revert condition has been met.
 non-payable-constructor | Consider making costructor payable to save gas.
 non-optimal-variables-swap | Consider swapping variables using `($VAR1, $VAR2) = ($VAR2, $VAR1)` to save gas.
+inefficient-state-variable-increment | <x> += <y> costs more gas than <x> = <x> + <y> for state variables.
 
 ## Best Practices Rules
 

solidity/performance/inefficient-state-variable-increment.sol

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.2;
+
+contract A {
+    uint256[10] public a;
+    uint256 public b;
+    function one() public {
+        a[0] = 4;
+        b = 5;
+        // ruleid: inefficient-state-variable-increment
+        a[0] += b;
+    }
+}
+
+
+contract B {
+    uint256 public a;
+    uint256 public b;
+    function one() public {
+        a = 4;
+        b = 5;
+        // ok: inefficient-state-variable-increment
+        a = a + b;
+    }
+}
+
+contract C {
+    uint256 public a = 4;
+    uint256 public b;
+    function one() public {
+        b = 5;
+        // ruleid: inefficient-state-variable-increment
+        a += b;
+    }
+}
+
+contract D {
+    function one() public {
+        a = 4;
+        b = 5;
+        // ok: inefficient-state-variable-increment
+        a += b;
+    }
+}
+
+contract E {
+    mapping (address => uint) public a;
+    function one() public {
+        // ok: inefficient-state-variable-increment
+        a[msg.sender] += 4;
+    }
+}

solidity/performance/inefficient-state-variable-increment.yaml

@@ -0,0 +1,37 @@
+rules:
+    -
+      id: inefficient-state-variable-increment
+      message: |
+        <x> += <y> costs more gas than <x> = <x> + <y> for state variables.
+      metadata:
+          references:
+          - https://gist.github.com/IllIllI000/cbbfb267425b898e5be734d4008d4fe8
+          category: performance
+          tags:
+          - plus-equal
+      patterns:
+        - pattern-either:
+          - pattern: |
+                $X += $Y
+          - pattern: |
+                $X[...] += $Y
+        - pattern-either:
+          - pattern-inside: |
+                contract $C {
+                  ...
+                  $TYPE $X;
+                  ...
+                }
+          - pattern-inside: |
+                contract $C {
+                  ...
+                  $TYPE $X = ...;
+                  ...
+                }
+        -  metavariable-regex:
+              metavariable: $TYPE
+              regex: uint
+      languages: 
+      - solidity
+      severity: INFO
+