Fixed type inference that may cause JIT failure

PHP allows to override a method that returns non-reference with a method
that returns a reference. This mean that we cannot use prototypes to
predict return types of a child functions.

Author: dstogov

Zend/Optimizer/zend_func_info.c

@@ -180,6 +180,10 @@ ZEND_API uint32_t zend_get_func_info(
 		if (!ret) {
 			ret = zend_get_return_info_from_signature_only(
 				callee_func, /* TODO: script */ NULL, ce, ce_is_instanceof, /* use_tentative_return_info */ !call_info->is_prototype);
+			/* It's allowed to override a method that return non-reference with a method that returns a reference */
+			if (call_info->is_prototype && (ret & ~MAY_BE_REF)) {
+				ret |= MAY_BE_REF;
+			}
 		}
 	}
 	return ret;

ext/opcache/tests/jit/ret_004.phpt

@@ -0,0 +1,28 @@
+--TEST--
+JIT RET: 004 Return a reference when it's not expected
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.file_update_protection=0
+opcache.jit_buffer_size=32M
+--FILE--
+<?php
+class A {
+	function foo() {
+	}
+	function bar() {
+		$x = $this->foo();
+		var_dump(str_repeat($x,5));
+	}
+}
+class B extends A {
+	public $prop = "x";
+	function &foo() {
+		return $this->prop;
+	}
+}
+$b = new B;
+$b->bar();
+?>
+--EXPECT--
+string(5) "xxxxx"