[Bug target/77468] [7 Regression] C-ray regression on Aarch64

[jgreenhalgh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77468

--- Comment #27 from James Greenhalgh <jgreenhalgh at gcc dot gnu.org> ---
(In reply to PeteVine from comment #25)
> The original issue never mentioned -Ofast or -ffast-math and I see no
> difference at -Ofast, indeed:
> 
> http://openbenchmarking.org/result/1702153-RI-CRAYFAST424
> 
> @jgreenhalgh Can you confirm there's no regression @ -O3 as well? Thanks.

I'm getting confused here by the number of bugs trying to multiplex on the same
report. Aldy's reproducer instructions are with -ffast-math, and that's what
I've used in my analysis. It seems you are more interested in a run without
-ffast-math, which is presumably a separate issue.

There is a useful lesson here for bug reporting. Upload a preprocessed file,
with an explicit set of flags, and the explicit configuration of the compiler
you are using. Having a solid description of the input you are concerned about
is more useful to me than annotated output - I can generate that myself! Don't
assume that because you have easy access to a file on the internet I also have
easy access to it, the best way to get code in front of me is with a
preprocessed file.

I'll take a look at what causes the performance difference between
-mcpu=cortex-a53 and -mcpu=thunderx. I'm now using the flags:

  -O3 -mcpu=cortex-a53 -lpthread -lm -fomit-frame-pointer -fipa-pta
-march=armv8-a+crc

and

  -O3 -mcpu=thunderx -lpthread -lm -fomit-frame-pointer -fipa-pta
-march=armv8-a+crc