From 75f911177506659ec773954b3409d5650be1222b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Marjam=C3=A4ki?= <daniel.marjamaki@gmail.com>
Date: Sat, 11 Jan 2014 15:36:09 +0100
Subject: [PATCH] value flow: bailout when variable is used in assignment to
 itself

---
 lib/valueflow.cpp      | 25 +++++++++++++++++++++++++
 test/testvalueflow.cpp |  8 ++++++++
 2 files changed, 33 insertions(+)

diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index f5eac13a9..675258db6 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -82,6 +82,24 @@ static const Token * skipValueInConditionalExpression(const Token *tok)
     return tok;
 }
 
+static bool bailoutSelfAssignment(const Token * const tok)
+{
+    const Token *parent = tok;
+    while (parent) {
+        const Token *op = parent;
+        parent = parent->astParent();
+
+        // Assignment where lhs variable exists in rhs => return true
+        if (parent                       != NULL         &&
+            parent->astOperand2()        == op           &&
+            parent->astOperand1()        != NULL         &&
+            parent->str()                == "="          &&
+            parent->astOperand1()->str() == tok->str())
+            return true;
+    }
+    return false;
+}
+
 static void valueFlowBeforeCondition(TokenList *tokenlist, ErrorLogger *errorLogger, const Settings *settings)
 {
     for (Token *tok = tokenlist->front(); tok; tok = tok->next()) {
@@ -152,6 +170,13 @@ static void valueFlowBeforeCondition(TokenList *tokenlist, ErrorLogger *errorLog
                     break;
                 }
 
+                // bailout: variable is used in rhs in assignment to itself
+                if (bailoutSelfAssignment(tok2)) {
+                    if (settings->debugwarnings)
+                        bailout(tokenlist, errorLogger, tok2, "variable " + tok2->str() + " is used in rhs in assignment to itself");
+                    break;
+                }
+
                 // assigned by subfunction?
                 if (bailoutFunctionPar(tok2)) {
                     if (settings->debugwarnings)
diff --git a/test/testvalueflow.cpp b/test/testvalueflow.cpp
index e12c712ee..78324fb1f 100644
--- a/test/testvalueflow.cpp
+++ b/test/testvalueflow.cpp
@@ -104,6 +104,14 @@ private:
                "}";
         ASSERT_EQUALS(true, testValueOfX(code, 3U, 123));
 
+        // assignment
+        code = "void f(int x) {\n"
+               "   x = 2 + x;\n"
+               "   if (x == 65);\n"
+               "}";
+        ASSERT_EQUALS(false, testValueOfX(code, 2U, 65));
+
+
         // guarding by &&
         code = "void f(int x) {\n"
                "    if (!x || \n"  // <- x can be 0