ValueFlow: Make known loop value possible

lib/valueflow.cpp

@@ -932,6 +932,23 @@ static bool valueFlowForward(Token * const               startToken,
                 return false;
             }
 
+            // if known variable is changed in loop body, change it to a possible value..
+            if (tok2->str() != "if") {
+                bool isChanged = false;
+                for (std::list<ValueFlow::Value>::iterator it = values.begin(); it != values.end(); ++it) {
+                    if (it->valueKind == ValueFlow::Value::Known) {
+                        if (!isChanged) {
+                            const Token *bodyStart = tok2->linkAt(1)->next();
+                            if (!isVariableChanged(bodyStart, bodyStart->link(), varid))
+                                break;
+                            isChanged = true;
+                        }
+
+                        it->valueKind = ValueFlow::Value::Possible;
+                    }
+                }
+            }
+
             // Set values in condition
             for (Token* tok3 = tok2->tokAt(2); tok3 != tok2->next()->link(); tok3 = tok3->next()) {
                 if (tok3->varId() == varid) {

test/testvalueflow.cpp

@@ -1566,6 +1566,16 @@ private:
         }
         ASSERT_EQUALS(true, possible);
 
+        code = "void f() {\n"
+               "  int x = 0;\n"
+               "  while (!x) {\n" // <- possible value
+               "    x = dostuff();\n"
+               "  }\n"
+               "}";
+        value = valueOfTok(code, "!");
+        ASSERT_EQUALS(1, value.intvalue);
+        ASSERT_EQUALS(ValueFlow::Value::ValueKind::Possible, value.valueKind);
+
         // after condition
         code = "int f(int x) {\n"
                "  if (x == 4) {}\n"