Fixed #5947 (valueFlowForward: forward conditions not handled properly)

lib/valueflow.cpp

@@ -128,6 +128,29 @@ static bool conditionIsFalse(const Token *condition, unsigned int varid, const V
     return !error && result == 0;
 }
 
+/**
+ * Is condition always true when variable has given value?
+ * \param condition   top ast token in condition
+ * \param varid       variable id for variable
+ * \param value       value of variable
+ */
+static bool conditionIsTrue(const Token *condition, unsigned int varid, const ValueFlow::Value &value)
+{
+    if (!condition)
+        return false;
+    if (condition->str() == "||") {
+        bool result1 = conditionIsTrue(condition->astOperand1(), varid, value);
+        bool result2 = result1 ? true : conditionIsTrue(condition->astOperand2(), varid, value);
+        return result2;
+    }
+    std::map<unsigned int, MathLib::bigint> programMemory;
+    programMemory[varid] = value.intvalue;
+    MathLib::bigint result = 0;
+    bool error = false;
+    execute(condition, &programMemory, &result, &error);
+    return !error && result == 1;
+}
+
 /**
  * Should value be skipped because it's hidden inside && || or ?: expression.
  * Example: ((x!=NULL) && (*x == 123))
@@ -558,6 +581,24 @@ static bool valueFlowForward(Token * const               startToken,
         if (Token::Match(tok2, "sizeof|typeof|typeid ("))
             tok2 = tok2->linkAt(1);
 
+        else if (Token::simpleMatch(tok2, "else {")) {
+            // Should scope be skipped because variable value is checked?
+            bool skipelse = false;
+            const Token *condition = tok2->linkAt(-1);
+            condition = condition ? condition->linkAt(-1) : nullptr;
+            condition = condition ? condition->astOperand2() : nullptr;
+            for (std::list<ValueFlow::Value>::iterator it = values.begin(); it != values.end(); ++it) {
+                if (conditionIsTrue(condition, varid, *it)) {
+                    skipelse = true;
+                    break;
+                }
+            }
+            if (skipelse) {
+                tok2 = tok2->linkAt(1);
+                continue;
+            }
+        }
+
         // conditional block of code that assigns variable..
         else if (Token::Match(tok2, "%var% (") && Token::simpleMatch(tok2->linkAt(1), ") {")) {
             // Should scope be skipped because variable value is checked?

test/testvalueflow.cpp

@@ -778,6 +778,17 @@ private:
                "}";
         ASSERT_EQUALS(true, testValueOfX(code, 3U, 3));
 
+        // conditional code after if/else/while
+        code = "void f(int x) {\n"
+               "  if (x == 2) {}\n"
+               "  if (x > 0)\n"
+               "    a = x;\n"
+               "  else\n"
+               "    b = x;\n"
+               "}";
+        ASSERT_EQUALS(true,  testValueOfX(code, 4U, 2));
+        ASSERT_EQUALS(false, testValueOfX(code, 6U, 2));
+
         // In condition, after && and ||
         code = "void f(int x) {\n"
                "  a = (x != 3 ||\n"