[Bug target/79964] Cortex A53 codegen still not optimal

[tulipawn at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79964

--- Comment #4 from PeteVine <tulipawn at gmail dot com> ---
> I'm not sure what you're trying to measure here - it's very confusing with multiple overlapping options (O3/Ofast/tree-vectorize), -mcpu/-march. Is it related to -fipa-pta or is that not relevant?

All the relevant flags have been kept constant (-Ofast -mcpu), so you should
only look at this result side by side with the previous one.

I'll summarise the findings for you:

To get the best c-ray performance out of gcc7 it's necessary to either use
-mcpu/mtune=cortex-a57 or -mcpu=cortex-a53 -frename-registers (depessimizing
with -mno-fix-cortex-a53-843419 if necessary)

However, in gcc8, neither produce the expected, best performance. No
combination does, a clear regression.