Fix 10289: ValueFlow; Wrong known value 'size_t - uint16_t > 0' (#3273)

lib/valueflow.cpp

@@ -431,6 +431,19 @@ static T calculate(const std::string& s, const T& x, const T& y)
 /** Set token value for cast */
 static void setTokenValueCast(Token *parent, const ValueType &valueType, const ValueFlow::Value &value, const Settings *settings);
 
+static bool isCompatibleValues(const ValueFlow::Value& value1, const ValueFlow::Value& value2)
+{
+    if (value1.isKnown() || value2.isKnown())
+        return true;
+    if (value1.isImpossible() || value2.isImpossible())
+        return false;
+    if (value1.varId == 0 || value2.varId == 0)
+        return true;
+    if (value1.varId == value2.varId && value1.varvalue == value2.varvalue && value1.isIntValue() && value2.isIntValue())
+        return true;
+    return false;
+}
+
 /** set ValueFlow value and perform calculations if possible */
 static void setTokenValue(Token* tok, const ValueFlow::Value &value, const Settings *settings)
 {
@@ -652,9 +665,8 @@ static void setTokenValue(Token* tok, const ValueFlow::Value &value, const Setti
                     continue;
                 if (value1.isIteratorValue() && value2.isIteratorValue())
                     continue;
-                if (value1.isKnown() || value2.isKnown() || value1.varId == 0 || value2.varId == 0 ||
+                if (!isCompatibleValues(value1, value2))
-                    (value1.varId == value2.varId && value1.varvalue == value2.varvalue && value1.isIntValue() &&
+                    continue;
-                     value2.isIntValue())) {
                 ValueFlow::Value result(0);
                 combineValueProperties(value1, value2, &result);
                 const double floatValue1 = value1.isIntValue() ? value1.intvalue : value1.floatValue;
@@ -705,7 +717,6 @@ static void setTokenValue(Token* tok, const ValueFlow::Value &value, const Setti
             }
         }
     }
-    }
 
     // !
     else if (parent->str() == "!") {

test/testvalueflow.cpp

@@ -5629,6 +5629,14 @@ private:
                "    return x;\n"
                "}\n";
         ASSERT_EQUALS(true, testValueOfXImpossible(code, 3U, -1));
+
+        code = "size_t g();\n"
+               "auto f(uint16_t j) {\n"
+               "    auto x = g() - j;\n"
+               "    return x;\n"
+               "}\n";
+        ASSERT_EQUALS(false, testValueOfXImpossible(code, 4U, 0));
+        ASSERT_EQUALS(true, testValueOfXImpossible(code, 4U, -1));
     }
 };