C/C++: Fixing minor issues in Useless Test query

Author: Yonah78

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

@@ -4,8 +4,7 @@
 <qhelp>
 
 <overview>
-<p>Comparisons operation like <code>a==8 && a!=7</code> contains an useless part : the non-equal part. This rule finds any test of this kind within an if or a while statement
-This rule will only find useless comparisons with a right literal operand. </p>
+<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>

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

@@ -1,6 +1,6 @@
 /**
  * @name Useless Test
- * @description Find any useless test of kind a==8 && a!=7
+ * @description A boolean condition that is guaranteed to never be evaluated should be deleted.
  * @kind problem
  * @problem.severity warning
  * @id cpp/uselesstest
@@ -9,16 +9,9 @@
  */
 
 import cpp
+import semmle.code.cpp.valuenumbering.GlobalValueNumbering
 
-predicate sameStmt(Expr e1, Expr e2) {
-  e1.getNumChild() = e2.getNumChild() and
-  e1.toString() = e2.toString() and
-  (
-    e1.getNumChild() = 0
-    or
-    forall(int i | i in [0 .. e1.getNumChild() - 1] | sameStmt(e1.getChild(i), e2.getChild(i)))
-  )
-}
+predicate sameExpr(Expr e1, Expr e2) { globalValueNumber(e1).getAnExpr() = e2 }
 
 Element nearestParent(Expr e) {
   if
@@ -38,13 +31,13 @@ where
     ne.getParent() instanceof LogicalAndExpr
   ) and
   (
-    eq.getChild(0) instanceof VariableAccess and ne.getChild(0) instanceof VariableAccess
+    eq.getLeftOperand() instanceof VariableAccess and ne.getLeftOperand() instanceof VariableAccess
     or
-    eq.getChild(0) instanceof PointerDereferenceExpr and
-    ne.getChild(0) instanceof PointerDereferenceExpr
+    eq.getLeftOperand() instanceof PointerDereferenceExpr and
+    ne.getLeftOperand() instanceof PointerDereferenceExpr
   ) and
-  eq.getChild(1) instanceof Literal and
-  ne.getChild(1) instanceof Literal and
+  eq.getRightOperand() instanceof Literal and
+  ne.getRightOperand() instanceof Literal and
   nearestParent(eq) = nearestParent(ne) and
-  sameStmt(eq.getChild(0), ne.getChild(0))
-select "Useless test", ne
+  sameExpr(eq.getLeftOperand(), ne.getLeftOperand())
+select "Useless test", ne