[github-flavored-markdown] github markdown colspan

There is no way to do so. Either use an HTML table, or put the same text on several cells.

like this:

| Can Reorder | 2nd operation |2nd operation |2nd operation |
| :---: | --- |
|1st operation|Normal Load <br/>Normal Store| Volatile Load <br/>MonitorEnter|Volatile Store<br/> MonitorExit|
|Normal Load <br/> Normal Store| | | No|
|Volatile Load <br/> MonitorEnter| No|No|No|
|Volatile store <br/> MonitorExit| | No|No|

which looks like

HTML table