Fixed incorrect DCE of a constructor call

Fixez oss-fuzz #42049

Author: dstogov

ext/opcache/Optimizer/dce.c

@@ -592,7 +592,10 @@ int dce_optimize_op_array(zend_op_array *op_array, zend_ssa *ssa, zend_bool reor
 		while ((i = zend_bitset_pop_first(ctx.instr_worklist, ctx.instr_worklist_len)) >= 0) {
 			zend_bitset_excl(ctx.instr_dead, i);
 			add_operands_to_worklists(&ctx, &op_array->opcodes[i], &ssa->ops[i], ssa, 1);
-			if (i < op_array->last && op_array->opcodes[i+1].opcode == ZEND_OP_DATA) {
+			if (i < op_array->last
+			 && (op_array->opcodes[i+1].opcode == ZEND_OP_DATA
+			  || (op_array->opcodes[i].opcode == ZEND_NEW
+			   && op_array->opcodes[i+1].opcode == ZEND_DO_FCALL))) {
 				zend_bitset_excl(ctx.instr_dead, i+1);
 				add_operands_to_worklists(&ctx, &op_array->opcodes[i+1], &ssa->ops[i+1], ssa, 1);
 			}

ext/opcache/tests/opt/dce_012.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Incorrect DCE of constructor DO_FCALL
+--FILE--
+<?php
+function test() {
+	$a = null;
+    for ($i = 0; $i < 10; $i++) {
+        $obj = $a = $a;
+        $obj = new stdClass;
+        $obj->orop1 = 'abc';
+    }
+
+    foreach (range(0, 6) as $levels) {
+        print "$levels level" . ($levels == C ? "" : "s") . "aaa";
+    }
+
+    $obj->prop1 = null;
+}
+test();
+?>
+--EXPECTF--
+Fatal error: Uncaught Error: Undefined constant "C" in %sdce_012.php:11
+Stack trace:
+#0 %sdce_012.php(16): test()
+#1 {main}
+  thrown in %sdce_012.php on line 11