[Bug c/70408] reusing the same call-preserved register would give smaller code in some cases

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70408

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|rtl-optimization            |c

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note teaching this trick requires a huge amount of work as you need to teach
GCC more about order of operands does not matter; this requires work in the
front-end and then in the gimple level and then maybe the middle-end.  

Is it worth it for the gain, most likely not, you are more likely just to get
better code by not depending on unspecified behavior in C.

># why lea instead of add rdi,2?

Because lea does not clobber the flags, so this might be faster, it depends on
the machine.

Also try -Os you might see a difference code.