[Bug target/81907] memset called when it does not need to be; -mtune=cortex-a9

[dongkyun.s at samsung dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81907

--- Comment #13 from dongkyun.s at samsung dot com ---
> Confirmed the call on 6.4.1 but GCC 7 and trunk don't generate the call for -mcpu=cortex-a9 .

I also verified memset call is not generated with GCC 7.1 + "-mcpu=cortex-a9 or
-mtune=cortex-a9" or lower.

It seems interesting that 
in GCC6,
- don't generate the memset call for -mcpu=cortex-a12 or higer(e.g, cortex-a15,
V7 big.LITTLE)
- always generate the memset call for -mcpu=cortex-a9 or lower(e.g, cortex-a7,
cotex-a5)

in GCC7.1
- always don't generate the memset call (even with V3 Architecture Processors.
e.g, -mcpu=arm7)