Introduce new CHECK_VAR instruction to keep warnings about undefined variables.

Author: dstogov

Zend/zend_vm_def.h

@@ -8100,6 +8100,19 @@ ZEND_VM_HANDLER(186, ZEND_ISSET_ISEMPTY_THIS, UNUSED, UNUSED)
 	ZEND_VM_NEXT_OPCODE();
 }
 
+ZEND_VM_HANDLER(49, ZEND_CHECK_VAR, CV, UNUSED)
+{
+	USE_OPLINE
+	zval *op1 = EX_VAR(opline->op1.var);
+
+	if (UNEXPECTED(Z_TYPE_INFO_P(op1) == IS_UNDEF)) {
+		SAVE_OPLINE();
+		GET_OP1_UNDEF_CV(op1, BP_VAR_R);
+		ZEND_VM_NEXT_OPCODE_CHECK_EXCEPTION();
+	}
+	ZEND_VM_NEXT_OPCODE();
+}
+
 ZEND_VM_TYPE_SPEC_HANDLER(ZEND_ADD, (res_info == MAY_BE_LONG && op1_info == MAY_BE_LONG && op2_info == MAY_BE_LONG), ZEND_ADD_LONG_NO_OVERFLOW, CONST|TMPVARCV, CONST|TMPVARCV, SPEC(NO_CONST_CONST,COMMUTATIVE))
 {
 	USE_OPLINE