ValueFlow: Improve bailout for structs etc in loops

lib/astutils.cpp

@@ -1419,6 +1419,31 @@ bool reaches(const Token * start, const Token * dest, const Library& library, Er
     return true;
 }
 
+static bool isUnchanged(const Token *startToken, const Token *endToken, const std::set<int> &exprVarIds, bool local)
+{
+    for (const Token *tok = startToken; tok != endToken; tok = tok->next()) {
+        if (!local && Token::Match(tok, "%name% (") && !Token::simpleMatch(tok->linkAt(1), ") {"))
+            // TODO: this is a quick bailout
+            return false;
+        if (tok->varId() <= 0 || exprVarIds.find(tok->varId()) == exprVarIds.end())
+            continue;
+        const Token *parent = tok;
+        while (parent->astParent() && !parent->astParent()->isAssignmentOp() && parent->astParent()->tokType() != Token::Type::eIncDecOp) {
+            if (parent->str() == "," || parent->isUnaryOp("&"))
+                // TODO: This is a quick bailout
+                return false;
+            parent = parent->astParent();
+        }
+        if (parent->astParent()) {
+            if (parent->astParent()->tokType() == Token::Type::eIncDecOp)
+                return false;
+            else if (parent->astParent()->isAssignmentOp() && parent == parent->astParent()->astOperand1())
+                return false;
+        }
+    }
+    return true;
+}
+
 struct FwdAnalysis::Result FwdAnalysis::checkRecursive(const Token *expr, const Token *startToken, const Token *endToken, const std::set<int> &exprVarIds, bool local, bool inInnerClass)
 {
     // Parse the given tokens
@@ -1515,8 +1540,25 @@ struct FwdAnalysis::Result FwdAnalysis::checkRecursive(const Token *expr, const
             return Result(Result::Type::BAILOUT);
 
         if (mWhat == What::ValueFlow && (Token::Match(tok, "while|for (") || Token::simpleMatch(tok, "do {"))) {
-            // TODO: only bailout if expr is reassigned in loop
+            const Token *bodyStart = nullptr;
-            return Result(Result::Type::BAILOUT);
+            const Token *conditionStart = nullptr;
+            if (Token::simpleMatch(tok, "do {")) {
+                bodyStart = tok->next();
+                if (Token::simpleMatch(bodyStart->link(), "} while ("))
+                    conditionStart = bodyStart->link()->tokAt(2);
+            } else {
+                conditionStart = tok->next();
+                if (Token::simpleMatch(conditionStart->link(), ") {"))
+                    bodyStart = conditionStart->link()->next();
+            }
+
+            // Is expr changed in condition?
+            if (!isUnchanged(conditionStart, conditionStart->link(), exprVarIds, local))
+                return Result(Result::Type::BAILOUT);
+
+            // Is expr changed in loop body?
+            if (!isUnchanged(bodyStart, bodyStart->link(), exprVarIds, local))
+                return Result(Result::Type::BAILOUT);
         }
 
         if (!local && Token::Match(tok, "%name% (") && !Token::simpleMatch(tok->linkAt(1), ") {")) {
@@ -1527,7 +1569,6 @@ struct FwdAnalysis::Result FwdAnalysis::checkRecursive(const Token *expr, const
         if (expr->isName() && Token::Match(tok, "%name% (") && tok->str().find("<") != std::string::npos && tok->str().find(expr->str()) != std::string::npos)
             return Result(Result::Type::BAILOUT);
 
-
         if (exprVarIds.find(tok->varId()) != exprVarIds.end()) {
             const Token *parent = tok;
             bool other = false;

test/testvalueflow.cpp

@@ -2567,6 +2567,19 @@ private:
         values = tokenValues(code, "<");
         ASSERT_EQUALS(true, values.empty());
 
+        code = "void f() {\n"
+               "  S s;\n"
+               "  s.x = 37;\n"
+               "  int y = 10;\n"
+               "  while (s.x < y)\n" // s.x has a known value
+               "    y--;\n"
+               "}";
+        values = tokenValues(code, ". x <");
+        ASSERT(values.size() == 1 &&
+               values.front().isKnown() &&
+               values.front().isIntValue() &&
+               values.front().intvalue == 37);
+
         code = "void f() {\n"
                "  Hints hints;\n"
                "  hints.x = 1;\n"