Fixed #8186 (Inner condition always false inside for loop)

lib/astutils.cpp

@@ -275,6 +275,17 @@ bool isOppositeCond(bool isNot, bool cpp, const Token * const cond1, const Token
             comp2[0] = '>';
     }
 
+    if (!isNot && comp2.empty()) {
+        if (isSameExpression(cpp, true, cond1->astOperand1(), cond2->astOperand1(), library, pure) &&
+            cond1->astOperand2() && cond1->astOperand2()->hasKnownIntValue() &&
+            cond2->astOperand2() && cond2->astOperand2()->hasKnownIntValue()) {
+            const ValueFlow::Value &rhsValue1 = cond1->astOperand2()->values().front();
+            const ValueFlow::Value &rhsValue2 = cond2->astOperand2()->values().front();
+            if (comp1 == "<" && cond2->str() == "==")
+                return (rhsValue1.intvalue < rhsValue2.intvalue);
+        }
+    }
+
     // is condition opposite?
     return ((comp1 == "==" && comp2 == "!=") ||
             (comp1 == "!=" && comp2 == "==") ||

lib/checkcondition.cpp

@@ -452,15 +452,35 @@ void CheckCondition::oppositeInnerCondition()
     const SymbolDatabase *symbolDatabase = _tokenizer->getSymbolDatabase();
 
     for (std::list<Scope>::const_iterator scope = symbolDatabase->scopeList.begin(); scope != symbolDatabase->scopeList.end(); ++scope) {
-        if (scope->type != Scope::eIf)
+        const Token *condTok = nullptr;
+        if (scope->type == Scope::eIf || scope->type == Scope::eWhile)
+            condTok = scope->classDef->next()->astOperand2();
+        else if (scope->type == Scope::eFor) {
+            condTok = scope->classDef->next()->astOperand2();
+            if (!condTok || condTok->str() != ";")
+                continue;
+            condTok = condTok->astOperand2();
+            if (!condTok || condTok->str() != ";")
+                continue;
+            condTok = condTok->astOperand1();
+        }
+        if (!condTok)
             continue;
+        const Token * const cond1 = condTok;
 
         if (!Token::simpleMatch(scope->classDef->linkAt(1), ") {"))
             continue;
 
         bool nonlocal = false; // nonlocal variable used in condition
         std::set<unsigned int> vars; // variables used in condition
-        for (const Token *cond = scope->classDef->linkAt(1); cond != scope->classDef; cond = cond->previous()) {
+        std::stack<const Token *> tokens;
+        tokens.push(condTok);
+        while (!tokens.empty()) {
+            const Token *cond = tokens.top();
+            tokens.pop();
+            if (!cond)
+                continue;
+
             if (cond->varId()) {
                 vars.insert(cond->varId());
                 const Variable *var = cond->variable();
@@ -470,6 +490,9 @@ void CheckCondition::oppositeInnerCondition()
             } else if (!nonlocal && cond->isName()) {
                 // varid is 0. this is possibly a nonlocal variable..
                 nonlocal = Token::Match(cond->astParent(), "%cop%|(");
+            } else {
+                tokens.push(cond->astOperand1());
+                tokens.push(cond->astOperand2());
             }
         }
 
@@ -514,7 +537,6 @@ void CheckCondition::oppositeInnerCondition()
             continue;
 
         // Condition..
-        const Token *cond1 = scope->classDef->next()->astOperand2();
         const Token *cond2 = ifToken->next()->astOperand2();
 
         if (isOppositeCond(false, _tokenizer->isCPP(), cond1, cond2, _settings->library, true))

test/testcondition.cpp

@@ -1574,6 +1574,14 @@ private:
               "  }\n"
               "}");
         ASSERT_EQUALS("", errout.str());
+
+        // #8186
+        check("void f() {\n"
+              "  for (int i=0;i<4;i++) {\n"
+              "    if (i==5) {}\n"
+              "  }\n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:2] -> [test.cpp:3]: (warning) Opposite conditions in nested 'if' blocks lead to a dead code block.\n", errout.str());
     }
 
     // clarify conditions with = and comparison