Merge pull request #7395 from MathiasVP/fix-fp-in-pointless-self-comparison

C++: Fix FP in `cpp/comparison-of-identical-expressions`

Author: geoffw0

cpp/ql/src/Likely Bugs/Arithmetic/ComparisonWithCancelingSubExpr.ql

@@ -85,7 +85,8 @@ private predicate cancelingSubExprs(ComparisonOperation cmp, VariableAccess a1,
   exists(Variable v |
     exists(float m | m < 0 and cmpLinearSubVariable(cmp, v, a1, m)) and
     exists(float m | m > 0 and cmpLinearSubVariable(cmp, v, a2, m))
-  )
+  ) and
+  not any(ClassTemplateInstantiation inst).getATemplateArgument() = cmp.getParent*()
 }
 
 from ComparisonOperation cmp, VariableAccess a1, VariableAccess a2

cpp/ql/src/Likely Bugs/Arithmetic/PointlessSelfComparison.qll

@@ -29,7 +29,9 @@ predicate pointlessSelfComparison(ComparisonOperation cmp) {
     not exists(lhs.getQualifier()) and // Avoid structure fields
     not exists(rhs.getQualifier()) and // Avoid structure fields
     not convertedExprMightOverflow(lhs) and
-    not convertedExprMightOverflow(rhs)
+    not convertedExprMightOverflow(rhs) and
+    // Don't warn if the comparison is part of a template argument.
+    not any(ClassTemplateInstantiation inst).getATemplateArgument() = cmp.getParent*()
   )
 }
 

cpp/ql/test/query-tests/Likely Bugs/Arithmetic/BadAdditionOverflowCheck/templates.cpp

@@ -20,3 +20,22 @@ bool compareValues() {
 bool callCompareValues() {
   return compareValues<C1, C2> || compareValues<C1, C1>();
 }
+
+template <bool C, typename T = void>
+struct enable_if {};
+
+template <typename T>
+struct enable_if<true, T> { typedef T type; };
+
+template<typename T1, typename T2>
+typename enable_if<T1::value <= T2::value, bool>::type constant_comparison() {
+  return true;
+}
+
+struct Value0 {
+  const static int value = 0;
+};
+
+void instantiation_with_pointless_comparison() {
+  constant_comparison<Value0, Value0>(); // GOOD
+}