[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 #13 from Arnd Bergmann <arnd at linaro dot org> ---
Created attachment 43185
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43185&action=edit
Linux kernel version of AES algorithm, ported to standalone executable

I've had another look at extracting a test case from the Linux kernel copy of
this code. This now also shows the gcc-7.2.1 specific problem:

$ x86_64-linux-gcc-7.1.1 -Wall -O2 -fsanitize=bounds -fsanitize=object-size
aes_generic.c -o aes_generic; time ./aes_generic
real    0m9.406s

$ x86_64-linux-gcc-7.1.1 -Wall -O2 -fsanitize=bounds -fsanitize=object-size
aes_generic.c -o aes_generic -fno-code-hoisting; time ./aes_generic
real    0m8.318s

$ x86_64-linux-gcc-7.2.1 -Wall -O2 -fsanitize=bounds -fsanitize=object-size
aes_generic.c -o aes_generic; time ./aes_generic
real    0m22.151s

$ x86_64-linux-gcc-7.2.1 -Wall -O2 -fsanitize=bounds -fsanitize=object-size
aes_generic.c -o aes_generic -fno-code-hoisting; time ./aes_generic
real    0m8.439s

$ x86_64-linux-gcc-7.1.1 -Wall -O2 aes_generic.c -o aes_generic ; time
./aes_generic
real    0m3.031s

$ x86_64-linux-gcc-7.1.1 -Wall -O2 aes_generic.c -o aes_generic
-fno-code-hoisting ; time ./aes_generic
real    0m2.894s

$ x86_64-linux-gcc-7.2.1 -Wall -O2 aes_generic.c -o aes_generic  ; time
./aes_generic
real    0m3.307s

$ x86_64-linux-gcc-7.2.1 -Wall -O2 aes_generic.c -o aes_generic
-fno-code-hoisting ; time ./aes_generic
real    0m2.875s