[Bug tree-optimization/83022] malloc & memset -> calloc is not always an optimization

[i at maskray dot me via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83022

--- Comment #6 from Fangrui Song <i at maskray dot me> ---
The issue succeeded to waste some time of MySQL developers BTW: 
http://smalldatum.blogspot.com/2017/11/a-new-optimization-in-gcc-5x-and-mysql.html