Fixed #7175 (False positive performance warning (buffer overwritten before its old content has been used))

lib/checkother.cpp

@@ -573,6 +573,19 @@ void CheckOther::checkRedundantAssignment()
                             if (it == memAssignments.end())
                                 memAssignments[param1->varId()] = tok;
                             else {
+                                bool read = false;
+                                for (const Token *tok2 = tok->linkAt(1); tok2 != writtenArgumentsEnd; tok2 = tok2->previous()) {
+                                    if (tok2->varId() == param1->varId()) {
+                                        // TODO: is this a read? maybe it's a write
+                                        read = true;
+                                        break;
+                                    }
+                                }
+                                if (read) {
+                                    memAssignments[param1->varId()] = tok;
+                                    continue;
+                                }
+
                                 if (printWarning && scope->type == Scope::eSwitch && Token::findmatch(it->second, "default|case", tok))
                                     redundantCopyInSwitchError(it->second, tok, param1->str());
                                 else if (printPerformance)

test/testother.cpp

@@ -5389,6 +5389,23 @@ private:
               "    return i;\n"
               "}");
         ASSERT_EQUALS("", errout.str());
+
+        // #7175 - read+write
+        check("void f() {\n"
+              "    char buf[100];\n"
+              "    strcpy(buf, x);\n"
+              "    strcpy(buf, dostuff(buf));\n" // <- read + write
+              "    strcpy(buf, x);\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        check("void f() {\n"
+              "    char buf[100];\n"
+              "    strcpy(buf, x);\n"
+              "    strcpy(buf, dostuff(buf));\n"
+              "    strcpy(buf, x);\n"
+              "}");
+        TODO_ASSERT_EQUALS("error", "", errout.str());
     }
 
     void varFuncNullUB() { // #4482