> Because most people agree that checking first and/or last
> byte/character is not a good idea (may be slower), here is a new patch
> removing code checking first/last byte or character in
> bytes_richcompare() and unicode_eq().

You misunderstood. Checking the first byte is ok, it's checking the last
byte which can misfire.

> It removes the usage of the "register" keyword, I read that modern
> compilers generate worse code when this keyword is used. Register
> allocators of modern compilers known better than you which variables
> should use a register.

I think you should open a separate issue to remove all instances of the
"register" keyword in the code base. It has become useless, any modern
compiler will allocate registers by itself, happily ignoring any
"register" hint.