Fix 11412: False positive: uninitvar (#4624)

* Dont remove modified variables from dead code

* Add test for 11412

* Format

Author: pfultz2

lib/forwardanalyzer.cpp

@@ -394,24 +394,24 @@ struct ForwardTraversal {
             return true;
         if (Token::simpleMatch(condTok, ":"))
             return true;
-        bool changed = false;
+        bool stepChangesCond = false;
         if (stepTok) {
             std::pair<const Token*, const Token*> exprToks = stepTok->findExpressionStartEndTokens();
             if (exprToks.first != nullptr && exprToks.second != nullptr)
-                changed |= isExpressionChanged(condTok, exprToks.first, exprToks.second->next(), settings, true);
+                stepChangesCond |= isExpressionChanged(condTok, exprToks.first, exprToks.second->next(), settings, true);
         }
-        changed |= isExpressionChanged(condTok, endBlock->link(), endBlock, settings, true);
+        const bool bodyChangesCond = isExpressionChanged(condTok, endBlock->link(), endBlock, settings, true);
         // Check for mutation in the condition
-        changed |= nullptr !=
-                   findAstNode(condTok, [&](const Token* tok) {
+        const bool condChanged =
+            nullptr != findAstNode(condTok, [&](const Token* tok) {
             return isVariableChanged(tok, 0, settings, true);
         });
+        const bool changed = stepChangesCond || bodyChangesCond || condChanged;
         if (!changed)
             return true;
         ForwardTraversal ft = fork(true);
-        ft.analyzer->assume(condTok, false, Analyzer::Assume::Absolute);
         ft.updateScope(endBlock);
-        return ft.isConditionTrue(condTok);
+        return ft.isConditionTrue(condTok) && bodyChangesCond;
     }
 
     Progress updateInnerLoop(Token* endBlock, Token* stepTok, Token* condTok) {

lib/programmemory.cpp

@@ -461,8 +461,12 @@ void ProgramMemoryState::assume(const Token* tok, bool b, bool isEmpty)
         programMemoryParseCondition(pm, tok, nullptr, settings, b);
     const Token* origin = tok;
     const Token* top = tok->astTop();
-    if (top && Token::Match(top->previous(), "for|while ("))
-        origin = top->link();
+    if (top && Token::Match(top->previous(), "for|while|if (") && !Token::simpleMatch(tok->astParent(), "?")) {
+        origin = top->link()->next();
+        if (!b && origin->link()) {
+            origin = origin->link();
+        }
+    }
     replace(pm, origin);
 }
 

lib/valueflow.cpp

@@ -2790,11 +2790,13 @@ struct ValueFlowAnalyzer : Analyzer {
             if (Token::simpleMatch(startBlock, ";") && Token::simpleMatch(parent->tokAt(-2), "} while ("))
                 startBlock = parent->linkAt(-2);
             const Token* endBlock = startBlock->link();
-            pms.removeModifiedVars(endBlock);
-            if (state)
+            if (state) {
+                pms.removeModifiedVars(endBlock);
                 pms.addState(endBlock->previous(), getProgramState());
-            else if (Token::simpleMatch(endBlock, "} else {"))
-                pms.addState(endBlock->linkAt(2)->previous(), getProgramState());
+            } else {
+                if (Token::simpleMatch(endBlock, "} else {"))
+                    pms.addState(endBlock->linkAt(2)->previous(), getProgramState());
+            }
         }
 
         if (!(flags & Assume::Quiet)) {

test/testuninitvar.cpp

@@ -5396,6 +5396,17 @@ class TestUninitVar : public TestFixture {
                         "    return n;\n"
                         "}\n");
         ASSERT_EQUALS("[test.cpp:4] -> [test.cpp:1]: (warning) Uninitialized variable: i\n", errout.str());
+
+        // #11412
+        valueFlowUninit("void f(int n) {\n"
+                        "	short* p;\n"
+                        "	if (n) {\n"
+                        "		p = g(n);\n"
+                        "	}\n"
+                        "	for (int i = 0; i < n; i++)\n"
+                        "		(void)p[i];\n"
+                        "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void valueFlowUninitBreak() { // Do not show duplicate warnings about the same uninitialized value