diff --git a/lib/astutils.cpp b/lib/astutils.cpp
index 58f421bf1d4..5b66f61ffc6 100644
--- a/lib/astutils.cpp
+++ b/lib/astutils.cpp
@@ -2474,6 +2474,11 @@ bool isVariableChangedByFunctionCall(const Token *tok, int indirect, const Setti
         return true;
     }
 
+    if (const Variable* var = tok->variable()) {
+        if (tok == var->nameToken() && (!var->isReference() || var->isConst()) && (var->isStlType() || !var->isClass())) // const ref or passed to (copy) ctor
+            return false;
+    }
+
     std::vector<const Variable*> args = getArgumentVars(tok, argnr);
     bool conclusive = false;
     for (const Variable *arg:args) {
diff --git a/lib/checkother.cpp b/lib/checkother.cpp
index 8e23a0617d9..4c88092638b 100644
--- a/lib/checkother.cpp
+++ b/lib/checkother.cpp
@@ -1547,7 +1547,7 @@ void CheckOther::checkConstPointer()
             else if (Token::Match(gparent, "%assign%") && parent == gparent->astOperand2()) {
                 bool takingRef = false, nonConstPtrAssignment = false;
                 const Token *lhs = gparent->astOperand1();
-                if (lhs && lhs->variable() && lhs->variable()->isReference() && lhs->variable()->nameToken() == lhs)
+                if (lhs && lhs->variable() && lhs->variable()->isReference() && lhs->variable()->nameToken() == lhs && !lhs->variable()->isConst())
                     takingRef = true;
                 if (lhs && lhs->valueType() && lhs->valueType()->pointer && (lhs->valueType()->constness & 1) == 0 &&
                     parent->valueType() && parent->valueType()->pointer)
diff --git a/lib/symboldatabase.cpp b/lib/symboldatabase.cpp
index 277c2848133..bffafe3eaa3 100644
--- a/lib/symboldatabase.cpp
+++ b/lib/symboldatabase.cpp
@@ -2381,7 +2381,7 @@ void Variable::evaluate(const Settings* settings)
         std::string strtype = mTypeStartToken->str();
         for (const Token *typeToken = mTypeStartToken; Token::Match(typeToken, "%type% :: %type%"); typeToken = typeToken->tokAt(2))
             strtype += "::" + typeToken->strAt(2);
-        setFlag(fIsClass, !lib->podtype(strtype) && !mTypeStartToken->isStandardType() && !isEnumType() && !isPointer() && !isReference() && strtype != "...");
+        setFlag(fIsClass, !lib->podtype(strtype) && !mTypeStartToken->isStandardType() && !isEnumType() && !isPointer() && strtype != "...");
         setFlag(fIsStlType, Token::simpleMatch(mTypeStartToken, "std ::"));
         setFlag(fIsStlString, ::isStlStringType(mTypeStartToken));
         setFlag(fIsSmartPointer, mTypeStartToken->isCpp() && lib->isSmartPointer(mTypeStartToken));
diff --git a/test/testnullpointer.cpp b/test/testnullpointer.cpp
index d67cd8329d8..5f76195af10 100644
--- a/test/testnullpointer.cpp
+++ b/test/testnullpointer.cpp
@@ -3717,7 +3717,7 @@ class TestNullPointer : public TestFixture {
         ASSERT_EQUALS("[test.cpp:9]: (error) Null pointer dereference: p\n"
                       "[test.cpp:10]: (error) Null pointer dereference: p\n"
                       "[test.cpp:11]: (error) Null pointer dereference: p\n"
-                      "[test.cpp:12]: (warning, inconclusive) Possible null pointer dereference: p\n"
+                      "[test.cpp:12]: (error) Null pointer dereference: p\n"
                       "[test.cpp:3]: (error) Null pointer dereference\n"
                       "[test.cpp:5]: (error) Null pointer dereference\n"
                       "[test.cpp:7]: (error) Null pointer dereference\n"
diff --git a/test/testother.cpp b/test/testother.cpp
index 6bce0a87d2f..4f12bf4f622 100644
--- a/test/testother.cpp
+++ b/test/testother.cpp
@@ -3479,6 +3479,47 @@ class TestOther : public TestFixture {
         ASSERT_EQUALS("[test.cpp:1]: (style) Parameter 'v' can be declared as reference to const\n"
                       "[test.cpp:8]: (style) Parameter 'v' can be declared as reference to const\n",
                       errout.str());
+
+        check("void cb(const std::string&);\n" // #12349, #12350, #12351
+              "void f(std::string& s) {\n"
+              "    const std::string& str(s);\n"
+              "    cb(str);\n"
+              "}\n"
+              "void g(std::string& s) {\n"
+              "    const std::string& str{ s };\n"
+              "    cb(str);\n"
+              "}\n"
+              "void h(std::string* s) {\n"
+              "    const std::string& str(*s);\n"
+              "    cb(str);\n"
+              "}\n"
+              "void k(std::string* s) {\n"
+              "    const std::string& str = *s;\n"
+              "    cb(str);\n"
+              "}\n"
+              "void m(std::string& s) {\n"
+              "    const std::string str(s);\n"
+              "    cb(str);\n"
+              "}\n"
+              "void n(std::string* s) {\n"
+              "    const std::string& str(*s);\n"
+              "    cb(str);\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:2]: (style) Parameter 's' can be declared as reference to const\n"
+                      "[test.cpp:6]: (style) Parameter 's' can be declared as reference to const\n"
+                      "[test.cpp:18]: (style) Parameter 's' can be declared as reference to const\n"
+                      "[test.cpp:10]: (style) Parameter 's' can be declared as pointer to const\n"
+                      "[test.cpp:14]: (style) Parameter 's' can be declared as pointer to const\n"
+                      "[test.cpp:22]: (style) Parameter 's' can be declared as pointer to const\n",
+                      errout.str());
+
+        check("struct S {\n"
+              "    S(std::string& r);\n"
+              "};\n"
+              "void f(std::string& str) {\n"
+              "    const S& s(str);\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void constParameterCallback() {
diff --git a/test/teststl.cpp b/test/teststl.cpp
index fb87b1c0a3b..05d0b8f070d 100644
--- a/test/teststl.cpp
+++ b/test/teststl.cpp
@@ -925,7 +925,7 @@ class TestStl : public TestFixture {
                     "    std::string_view sv(s);\n"
                     "    return s[2];\n"
                     "}\n");
-        TODO_ASSERT_EQUALS("test.cpp:4:error:Out of bounds access in expression 's[2]' because 's' is empty.\n", "", errout.str());
+        ASSERT_EQUALS("test.cpp:4:error:Out of bounds access in expression 's[2]' because 's' is empty.\n", errout.str());
     }
 
     void outOfBoundsSymbolic()
diff --git a/test/testuninitvar.cpp b/test/testuninitvar.cpp
index a4c7a78c5a6..57209f0f9bf 100644
--- a/test/testuninitvar.cpp
+++ b/test/testuninitvar.cpp
@@ -5562,7 +5562,7 @@ class TestUninitVar : public TestFixture {
                         "        p = new S(io);\n"
                         "    p->Write();\n"
                         "}");
-        ASSERT_EQUALS("[test.cpp:8] -> [test.cpp:10]: (warning) Uninitialized variable: p.rIo\n", errout.str());
+        ASSERT_EQUALS("", errout.str());
 
         // Unknown types
         {