Improve the optimizer's check if a function is a prototype or not

Currently, a function is considered a prototype if the function is not
marked as final. However, a class marked as final or an anonymous class
also make it impossible for a function to be overridden. Therefore, we
know in these 2 cases too that the function is not a prototype.
This allows the type inference algorithm to determine some types more
precisely, and can allow for more optimizations of the instructions.
Additionally, place some computation of the flags in their respective
blocks as a micro-optimization.

Author: nielsdos

Zend/Optimizer/zend_optimizer.c

@@ -891,16 +891,20 @@ zend_function *zend_optimizer_get_called_func(
 					&op_array->scope->function_table, method_name);
 				if (fbc) {
 					bool is_private = (fbc->common.fn_flags & ZEND_ACC_PRIVATE) != 0;
-					bool is_final = (fbc->common.fn_flags & ZEND_ACC_FINAL) != 0;
-					bool same_scope = fbc->common.scope == op_array->scope;
 					if (is_private) {
 						/* Only use private method if in the same scope. We can't even use it
 						 * as a prototype, as it may be overridden with changed signature. */
+						bool same_scope = fbc->common.scope == op_array->scope;
 						return same_scope ? fbc : NULL;
 					}
-					/* If the method is non-final, it may be overridden,
-					 * but only with a compatible method signature. */
-					*is_prototype = !is_final;
+					/* Prototype methods are potentially overridden. fbc still contains useful type information.
+					 * Some optimizations may not be applied, like inlining or inferring the send-mode of superfluous args.
+					 * A method cannot be overridden if the class or method is final. */
+					bool can_be_overridden = (fbc->common.fn_flags & ZEND_ACC_FINAL) == 0 &&
+											 (fbc->common.scope->ce_flags & ZEND_ACC_FINAL) == 0;
+					if (can_be_overridden) {
+						*is_prototype = true;
+					}
 					return fbc;
 				}
 			}

ext/opcache/tests/opt/type_inference_final_class.phpt

@@ -0,0 +1,42 @@
+--TEST--
+Type inference test with final class
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.optimization_level=-1
+opcache.opt_debug_level=0x20000
+opcache.preload=
+--EXTENSIONS--
+opcache
+--FILE--
+<?php
+
+final class Test {
+    public function getInt(): int {
+        return 42;
+    }
+    public function getInt2(): int {
+        return $this->getInt();
+    }
+}
+
+?>
+--EXPECTF--
+$_main:
+     ; (lines=1, args=0, vars=0, tmps=0)
+     ; (after optimizer)
+     ; %s
+0000 RETURN int(1)
+
+Test::getInt:
+     ; (lines=1, args=0, vars=0, tmps=0)
+     ; (after optimizer)
+     ; %s
+0000 RETURN int(42)
+
+Test::getInt2:
+     ; (lines=2, args=0, vars=0, tmps=1)
+     ; (after optimizer)
+     ; %s
+0000 V0 = QM_ASSIGN int(42)
+0001 RETURN V0