[Bug middle-end/82658] Suboptimal codegen on AVR when right-shifting 8-bit unsigned integers.

["mike.k at digitalcarbide dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82658

--- Comment #2 from mike.k at digitalcarbide dot com ---
I wanted to validate if this issue was presenting in the toolchains for other
architectures, so I tested a bit:

GCC 7.2.0 on x86-64 (-O3):

C:

movzx   eax, BYTE PTR [rsp-1]
shr     al
mov     BYTE PTR [rsp-1], al
ret

C++:

movzx   eax, BYTE PTR [rsp-1]
sar     eax
mov     BYTE PTR [rsp-1], al
ret

While not different in performance, it _is_ generating different code, and the
code difference seems to reflect what Richard already found.

I am not able to reproduce any difference on MIPS64, MIPS32, ARM, ARM64, PPC,
PPC64. This is probably due to backend differences not causing the sequences to
map differently.

I do see it going back to GCC 4.6.4 on AVR.