[Bug tree-optimization/40748] simple switch/case, if/else and arithmetics result in different code

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40748

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |tree-optimization

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So we handle f1 and foo correctly since GCC 9 (well almost, f1 is handled
correctly on the trunk that is turn into MIN_EXPR which happens because PHI-OPT
uses match-and-simplify which was done in r12-1152).

f3 has always been handled.

f2 is the one which is not handled, GCC knows how to convert it to a switch
table but does not because of "cost".

Here is a similar function which messes up GCC and LLVM fully and never
recovers (for GCC it started in 11, for clang it started in clang 12):
unsigned f2(unsigned i)
{
        if (i == 0) return 0;
        if (i == 1) return 1;
        if (i == 2) return 2;
        if (i == 3) return 3;
        if (i == 4) return 4;
        if (i == 5) return 4;
        if (i == 6) return 4;
        return 4;
}