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DeadCode: Add MISRA C 2012 Rule 2.2
Add support for Rule 2.2 by adoptiing the DeadCode shared query. A small modification has been made to ensure results which include macro expansions are reported, unless the macro fully generates the statement.
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‎c/common/test/rules/deadcode/DeadCode.expected‎

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| test.c:20:3:20:27 | declaration | This statement is dead code. |
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| test.c:21:3:21:12 | ExprStmt | This statement is dead code. |
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| test.c:22:3:22:12 | ExprStmt | This statement is dead code. |
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| test.c:24:3:26:3 | if (...) ... | This statement is dead code. |
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| test.c:36:3:37:3 | if (...) ... | This statement is dead code. |
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| test.c:39:3:39:4 | { ... } | This statement is dead code. |
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| test.c:40:3:42:3 | { ... } | This statement is dead code. |
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| test.c:56:6:57:3 | { ... } | This statement is dead code. |
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| test.c:67:46:68:3 | { ... } | This statement is dead code. |
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| test.c:71:3:71:8 | ExprStmt | This statement is dead code. |
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| test.c:73:3:73:21 | ExprStmt | This statement is dead code. |

‎c/common/test/rules/deadcode/DeadCode.ql‎

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// GENERATED FILE - DO NOT MODIFY
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import codingstandards.cpp.rules.deadcode.DeadCode

‎c/common/test/rules/deadcode/test.c‎

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// NOTICE: THE TEST CASES BELOW ARE ALSO INCLUDED IN THE C++ TEST CASE AND CHANGES
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// SHOULD BE REFLECTED THERE AS WELL.
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// Define true/false for compatibility with C++ test cases
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#define false 0
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#define true 1
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int may_have_side_effects();
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int no_side_effects(int x) { return 1 + 2; }
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int no_side_effects_nondeterministic();
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int test_dead_code(int x) {
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int live1 = may_have_side_effects(),
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live2 = may_have_side_effects(); // COMPLIANT
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int live3 = 0,
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live4 = may_have_side_effects(); // COMPLIANT
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int live5 = 0, live6 = 0; // COMPLIANT
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live5 = 1; // COMPLIANT
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live6 = 2; // COMPLIANT
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int dead1 = 0, dead2 = 0; // NON_COMPLIANT
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dead1 = 1; // NON_COMPLIANT - useless assignment
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dead2 = 1; // NON_COMPLIANT - useless assignment
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if (false) { // NON_COMPLIANT
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dead2 = 10; // Only used in dead or unreachable code
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}
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if (true) { // COMPLIANT
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may_have_side_effects();
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}
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if (may_have_side_effects()) { // COMPLIANT
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may_have_side_effects();
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}
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if (true) { // NON_COMPLIANT
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}
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{} // NON_COMPLIANT
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{ // NON_COMPLIANT
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1 + 2;
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}
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{ // COMPLIANT
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may_have_side_effects();
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}
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do { // COMPLIANT
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may_have_side_effects();
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} while (may_have_side_effects());
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do { // COMPLIANT
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may_have_side_effects();
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} while (may_have_side_effects());
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do { // NON_COMPLIANT
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} while (no_side_effects_nondeterministic());
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while (may_have_side_effects()) { // COMPLIANT
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may_have_side_effects();
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}
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while (may_have_side_effects()) { // COMPLIANT
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may_have_side_effects();
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}
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while (no_side_effects_nondeterministic()) { // NON_COMPLIANT
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}
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may_have_side_effects(); // COMPLIANT
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1 + 2; // NON_COMPLIANT
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no_side_effects(x); // NON_COMPLIANT
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return live5 + live6; // COMPLIANT
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}

‎c/misra/src/rules/RULE-2-2/DeadCode.ql‎

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/**
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* @id c/misra/dead-code
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* @name RULE-2-2: There shall be no dead code
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* @description Dead code complicates the program and can indicate a possible mistake on the part of
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* the programmer.
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* @kind problem
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* @precision very-high
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* @problem.severity warning
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* @tags external/misra/id/rule-2-2
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* readability
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* maintainability
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* external/misra/obligation/required
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*/
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import cpp
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import codingstandards.c.misra
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import codingstandards.cpp.rules.deadcode.DeadCode
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class MisraCDeadCodeQuery extends DeadCodeSharedQuery {
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MisraCDeadCodeQuery() { this = DeadCodePackage::deadCodeQuery() }
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}

‎c/misra/test/rules/RULE-2-2/DeadCode.testref‎

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c/common/test/rules/deadcode/DeadCode.ql

‎change_notes/2023-01-11-dead-code-macros.md‎

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- `M0-1-9`: This query previously excluded all results which were affected by a macro expansion. This is because a macro may be expanded multiple times with code that is dead in one expansion but live in another. This query has been modified to exclude results only where the entirety of a statement is generated by a macro. This reduces false negatives where the statements liveness is not affected by the macro expansion.

‎cpp/common/src/codingstandards/cpp/rules/deadcode/DeadCode.qll‎

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// MISRA defines dead code as an "_executed_ statement whose removal would not affect the program
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// output". We therefore exclude unreachable statements as they are, by definition, not executed.
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not s.getBasicBlock() = any(UnreachableBasicBlock ubb).getABasicBlock() and
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// Exclude code generated by macros, because the code may be "live" in other instantiations
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not s.isAffectedByMacro() and
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// Exclude code fully generated by macros, because the code may be "live" in other expansions
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not s.isInMacroExpansion() and
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// Exclude compiler generated statements
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not s.isCompilerGenerated()
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}

‎cpp/common/test/rules/deadcode/DeadCode.expected‎

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| test.cpp:14:3:14:27 | declaration | This statement is dead code. |
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| test.cpp:15:3:15:12 | ExprStmt | This statement is dead code. |
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| test.cpp:16:3:16:12 | ExprStmt | This statement is dead code. |
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| test.cpp:18:3:20:3 | if (...) ... | This statement is dead code. |
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| test.cpp:30:3:31:3 | if (...) ... | This statement is dead code. |
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| test.cpp:33:3:33:4 | { ... } | This statement is dead code. |
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| test.cpp:34:3:36:3 | { ... } | This statement is dead code. |
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| test.cpp:50:6:51:3 | { ... } | This statement is dead code. |
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| test.cpp:61:46:62:3 | { ... } | This statement is dead code. |
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| test.cpp:65:3:65:8 | ExprStmt | This statement is dead code. |
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| test.cpp:67:3:67:21 | ExprStmt | This statement is dead code. |
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| test.cpp:69:3:70:3 | try { ... } | This statement is dead code. |
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| test.cpp:70:17:71:3 | { ... } | This statement is dead code. |
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| test.cpp:76:17:77:3 | { ... } | This statement is dead code. |
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| test.cpp:17:3:17:27 | declaration | This statement is dead code. |
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| test.cpp:18:3:18:12 | ExprStmt | This statement is dead code. |
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| test.cpp:19:3:19:12 | ExprStmt | This statement is dead code. |
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| test.cpp:21:3:23:3 | if (...) ... | This statement is dead code. |
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| test.cpp:33:3:34:3 | if (...) ... | This statement is dead code. |
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| test.cpp:36:3:36:4 | { ... } | This statement is dead code. |
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| test.cpp:37:3:39:3 | { ... } | This statement is dead code. |
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| test.cpp:53:6:54:3 | { ... } | This statement is dead code. |
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| test.cpp:64:46:65:3 | { ... } | This statement is dead code. |
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| test.cpp:68:3:68:8 | ExprStmt | This statement is dead code. |
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| test.cpp:70:3:70:21 | ExprStmt | This statement is dead code. |
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| test.cpp:72:3:73:3 | try { ... } | This statement is dead code. |
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| test.cpp:73:17:74:3 | { ... } | This statement is dead code. |
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| test.cpp:79:17:80:3 | { ... } | This statement is dead code. |

‎cpp/common/test/rules/deadcode/test.cpp‎

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// NOTICE: THE TEST CASES BELOW ARE ALSO INCLUDED IN THE C TEST CASE AND CHANGES
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// SHOULD BE REFLECTED THERE AS WELL.
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int may_have_side_effects();
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int no_side_effects(int x) { return 1 + 2; }
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int no_side_effects_nondeterministic();

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