Fixed #7006 (False positive Mismatching assignment and comparison (variable is changed in loop))

lib/astutils.cpp

@@ -271,3 +271,36 @@ bool isWithoutSideEffects(bool cpp, const Token* tok)
     return true;
 }
 
+bool isVariableChanged(const Token *start, const Token *end, const unsigned int varid)
+{
+    for (const Token *tok = start; tok != end; tok = tok->next()) {
+        if (tok->varId() == varid) {
+            if (Token::Match(tok, "%name% =|++|--"))
+                return true;
+
+            if (Token::Match(tok->previous(), "++|-- %name%"))
+                return true;
+
+            if (Token::Match(tok->tokAt(-2), "[(,] & %var% [,)]"))
+                return true; // TODO: check if function parameter is const
+
+            if (Token::Match(tok->previous(), "[(,] %var% [,)]")) {
+                const Token *parent = tok->astParent();
+                while (parent && parent->str() == ",")
+                    parent = parent->astParent();
+                if (parent && parent->str() == "(") {
+                    if (parent->astOperand1() && parent->astOperand1()->isName() && !parent->astOperand1()->function())
+                        return true;
+                    // TODO: check if function parameter is non-const reference etc..
+                }
+            }
+
+            const Token *parent = tok->astParent();
+            while (Token::Match(parent, ".|::"))
+                parent = parent->astParent();
+            if (parent && parent->tokType() == Token::eIncDecOp)
+                return true;
+        }
+    }
+    return false;
+}

lib/astutils.h

@@ -64,4 +64,7 @@ bool isConstExpression(const Token *tok, const std::set<std::string> &constFunct
 
 bool isWithoutSideEffects(bool cpp, const Token* tok);
 
+/** Is variable changed in block of code? */
+bool isVariableChanged(const Token *start, const Token *end, const unsigned int varid);
+
 #endif // astutilsH

lib/checkcondition.cpp

@@ -142,6 +142,13 @@ bool CheckCondition::assignIfParseScope(const Token * const assignTok,
         if (Token::Match(tok2, "if|while (")) {
             if (!islocal && tok2->str() == "while")
                 continue;
+            if (tok2->str() == "while") {
+                // is variable changed in loop?
+                const Token *bodyStart = tok2->linkAt(1)->next();
+                const Token *bodyEnd   = bodyStart ? bodyStart->link() : nullptr;
+                if (!bodyEnd || bodyEnd->str() != "}" || isVariableChanged(bodyStart, bodyEnd, varid))
+                    continue;
+            }
 
             // parse condition
             const Token * const end = tok2->next()->link();

lib/valueflow.cpp

@@ -17,6 +17,7 @@
  */
 
 #include "valueflow.h"
+#include "astutils.h"
 #include "errorlogger.h"
 #include "mathlib.h"
 #include "settings.h"
@@ -321,40 +322,6 @@ static bool isReturn(const Token *tok)
     return false;
 }
 
-static bool isVariableChanged(const Token *start, const Token *end, const unsigned int varid)
-{
-    for (const Token *tok = start; tok != end; tok = tok->next()) {
-        if (tok->varId() == varid) {
-            if (Token::Match(tok, "%name% =|++|--"))
-                return true;
-
-            if (Token::Match(tok->previous(), "++|-- %name%"))
-                return true;
-
-            if (Token::Match(tok->tokAt(-2), "[(,] & %var% [,)]"))
-                return true; // TODO: check if function parameter is const
-
-            if (Token::Match(tok->previous(), "[(,] %var% [,)]")) {
-                const Token *parent = tok->astParent();
-                while (parent && parent->str() == ",")
-                    parent = parent->astParent();
-                if (parent && parent->str() == "(") {
-                    if (parent->astOperand1() && parent->astOperand1()->isName() && !parent->astOperand1()->function())
-                        return true;
-                    // TODO: check if function parameter is non-const reference etc..
-                }
-            }
-
-            const Token *parent = tok->astParent();
-            while (Token::Match(parent, ".|::"))
-                parent = parent->astParent();
-            if (parent && parent->tokType() == Token::eIncDecOp)
-                return true;
-        }
-    }
-    return false;
-}
-
 /** Add token value. Return true if value is added. */
 static bool addValue(Token *tok, const ValueFlow::Value &value)
 {

test/testcondition.cpp

@@ -178,6 +178,15 @@ private:
               "}");
         ASSERT_EQUALS("", errout.str());
 
+        check("void f(int x) {\n"
+              "    int a = 100;\n"
+              "    while (x) {\n"
+              "        int y = 16 | a;\n"
+              "        while (y != 0) y--;\n"
+              "    }\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
         // calling function
         check("void f(int x) {\n"
               "    int y = x & 7;\n"