Merge pull request #7787 from Yonah125/main

C/C++ : Useless test

Author: MathiasVP

cpp/ql/src/experimental/Best Practices/UselessTest.cpp

@@ -0,0 +1,9 @@
+void test(){
+    int a = 8;
+    int b = 9;
+
+    //Useless NonEquals
+    if(a==8 && a != 7) {}
+
+    while(a==8 && a!=7){}
+}

cpp/ql/src/experimental/Best Practices/UselessTest.qhelp

@@ -0,0 +1,18 @@
+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+
+<overview>
+<p>Comparison operations like <code>a==8 &amp;&amp; a!=7</code> contain a useless part : the non-equal part. This rule finds tests of this kind within an <code>if</code> or a <code>while</code> statement</p>
+</overview>
+
+<recommendation>
+<p>Remove the useless comparisons</p>
+</recommendation>
+
+<example>
+<sample src="UselessTest.cpp" />
+</example>
+
+</qhelp>

cpp/ql/src/experimental/Best Practices/UselessTest.ql

@@ -0,0 +1,43 @@
+/**
+ * @name Useless Test
+ * @description A boolean condition that is guaranteed to never be evaluated should be deleted.
+ * @kind problem
+ * @problem.severity warning
+ * @id cpp/uselesstest
+ * @tags reliability
+ *       readability
+ */
+
+import cpp
+import semmle.code.cpp.valuenumbering.GlobalValueNumbering
+
+predicate sameExpr(Expr e1, Expr e2) { globalValueNumber(e1).getAnExpr() = e2 }
+
+Element nearestParent(Expr e) {
+  if
+    e.getParent().(Expr).getConversion*() instanceof ParenthesisExpr or
+    e.getParent() instanceof IfStmt or
+    e.getParent() instanceof WhileStmt
+  then result = e.getParent()
+  else result = nearestParent(e.getParent())
+}
+
+from LogicalAndExpr b, EQExpr eq, NEExpr ne
+where
+  (
+    b.getAChild*() = eq and
+    b.getAChild*() = ne and
+    eq.getParent() instanceof LogicalAndExpr and
+    ne.getParent() instanceof LogicalAndExpr
+  ) and
+  (
+    eq.getLeftOperand() instanceof VariableAccess and ne.getLeftOperand() instanceof VariableAccess
+    or
+    eq.getLeftOperand() instanceof PointerDereferenceExpr and
+    ne.getLeftOperand() instanceof PointerDereferenceExpr
+  ) and
+  eq.getRightOperand() instanceof Literal and
+  ne.getRightOperand() instanceof Literal and
+  nearestParent(eq) = nearestParent(ne) and
+  sameExpr(eq.getLeftOperand(), ne.getLeftOperand())
+select ne, "Useless Test"