[Bug tree-optimization/83651] [7/8 regression] 20% slowdown of linux kernel AES cipher

[arnd at linaro dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83651

--- Comment #6 from Arnd Bergmann <arnd at linaro dot org> ---
Created attachment 43177
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43177&action=edit
Single-file version of aes benchmark

I've managed to condense the 'openssl speed aes-256-cbc' test into a single
file now:

$ x86_64-linux-gcc-7.2.1 -Wall -O2 aes_test.c -o aes_test
$ time ./aes_test
real    0m4.499s
user    0m4.498s
sys     0m0.000s

$ x86_64-linux-gcc-7.2.1 -Wall -O2 aes_test.c -o aes_test -fno-code-hoisting
$ time ./aes_test
real    0m4.135s
user    0m4.134s
sys     0m0.000s

The test is hardcoded to do 100000 runs of of 8192 bytes, so on my 3.1GHz CPU
that translates cyles:
$ echo $[4999 * 310000000  / 819200000]
1891 # 18.91 cycles
$ echo $[4135 * 310000000  / 819200000]
1564 # 15.6 cycles

Similar results with gcc-8.0.0:

$ x86_64-linux-gcc-8.0.0 -Wall -O2 aes_test.c -o aes_test
$ time ./aes_test
real    0m4.471s
user    0m4.470s
sys     0m0.000s

$ x86_64-linux-gcc-8.0.0 -Wall -O2 aes_test.c -o aes_test -fno-code-hoisting
$ time ./aes_test
real    0m4.052s
user    0m4.052s
sys     0m0.000s

Hope that helps