Warn when incrementing uninitialized value (#4042)

* Warn when incrementing uninitialized value

* Format

Author: pfultz2

lib/checkuninitvar.cpp

@@ -1579,7 +1579,7 @@ static ExprUsage getExprUsage(const Token* tok, int indirect, const Settings* se
         if (tok->astParent()->isCast())
             return ExprUsage::NotUsed;
     }
-    if (indirect == 0 && Token::Match(tok->astParent(), "%cop%|%assign%") && tok->astParent()->str() != "=")
+    if (indirect == 0 && Token::Match(tok->astParent(), "%cop%|%assign%|++|--") && tok->astParent()->str() != "=")
         return ExprUsage::Used;
     return getFunctionUsage(tok, indirect, settings);
 }

test/testuninitvar.cpp

@@ -5285,6 +5285,12 @@ class TestUninitVar : public TestFixture {
                         "    g(p->x);\n"
                         "}\n");
         ASSERT_EQUALS("[test.cpp:7] -> [test.cpp:8]: (error) Uninitialized variable: p->x\n", errout.str());
+
+        valueFlowUninit("void f() {\n"
+                        "    int a;\n"
+                        "    a++;\n"
+                        "}\n");
+        ASSERT_EQUALS("[test.cpp:3]: (error) Uninitialized variable: a\n", errout.str());
     }
 
     void valueFlowUninitBreak() { // Do not show duplicate warnings about the same uninitialized value