Merge branch 'PHP-7.4'

* PHP-7.4:
  Fixed bug #77345 (Stack Overflow caused by circular reference in garbage collection)
  Add support for MemorySanitizer

Author: dstogov

Zend/tests/bug77345_gc_1.phpt

@@ -0,0 +1,42 @@
+--TEST--
+Bug #77345 (Segmentation faults stack overflow in cyclic garbage collector) (Bug #77427)
+--INI--
+zend.enable_gc = 1
+--FILE--
+<?php
+
+class Node
+{
+    /** @var Node */
+    public $previous;
+    /** @var Node */
+    public $next;
+}
+
+var_dump(gc_enabled());
+var_dump('start');
+
+$firstNode = new Node();
+$firstNode->previous = $firstNode;
+$firstNode->next = $firstNode;
+
+$circularDoublyLinkedList = $firstNode;
+
+for ($i = 0; $i < 200000; $i++) {
+    $currentNode = $circularDoublyLinkedList;
+    $nextNode = $circularDoublyLinkedList->next;
+
+    $newNode = new Node();
+
+    $newNode->previous = $currentNode;
+    $currentNode->next = $newNode;
+    $newNode->next = $nextNode;
+    $nextNode->previous = $newNode;
+
+    $circularDoublyLinkedList = $nextNode;
+}
+var_dump('end');
+--EXPECT--
+bool(true)
+string(5) "start"
+string(3) "end"

Zend/tests/bug77345_gc_2.phpt

@@ -0,0 +1,48 @@
+--TEST--
+Bug #77345 (Segmentation faults stack overflow in cyclic garbage collector) (Bug #77427)
+--INI--
+zend.enable_gc = 1
+--FILE--
+<?php
+
+class Node
+{
+    /** @var Node */
+    public $previous;
+    /** @var Node */
+    public $next;
+}
+
+var_dump(gc_enabled());
+var_dump('start');
+
+function xxx() {
+    $firstNode = new Node();
+    $firstNode->previous = $firstNode;
+    $firstNode->next = $firstNode;
+
+    $circularDoublyLinkedList = $firstNode;
+
+    for ($i = 0; $i < 300000; $i++) {
+        $currentNode = $circularDoublyLinkedList;
+        $nextNode = $circularDoublyLinkedList->next;
+
+        $newNode = new Node();
+
+        $newNode->previous = $currentNode;
+        $currentNode->next = $newNode;
+        $newNode->next = $nextNode;
+        $nextNode->previous = $newNode;
+
+        $circularDoublyLinkedList = $nextNode;
+    }
+}
+
+xxx();
+gc_collect_cycles();
+
+var_dump('end');
+--EXPECT--
+bool(true)
+string(5) "start"
+string(3) "end"