[Bug rtl-optimization/93565] [9/10 regression] Combine duplicates instructions

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93565

--- Comment #19 from Segher Boessenkool <segher at gcc dot gnu.org> ---
With that above patch, I get (T0 is original, T2 is with patch, these are
file sizes of a Linux build, mostly defconfig):

                    T0        T2
       alpha   6049096  100.020%
         arc   4019384  100.000%
         arm  14177962   99.999%
       arm64  12968466   99.938%
         c6x   2346077  100.000%
        csky   3332454  100.000%
       h8300   1165256   99.999%
        i386  11227764  100.001%
        ia64  18088488  100.003%
        m68k   3716871  100.000%
  microblaze   4935181  100.000%
        mips   8407681  100.000%
      mips64   6979344   99.987%
       nds32   4471023  100.000%
       nios2   3643253  100.000%
    openrisc   4182200  100.000%
      parisc   7710095  100.001%
    parisc64   8676725  100.003%
     powerpc  10603859  100.000%
   powerpc64  17552718  100.007%
 powerpc64le  17552718  100.007%
     riscv32   1546172  100.000%
     riscv64   6623170  100.010%
        s390  13103095   99.995%
          sh   3216555   99.999%
     shnommu   1611176   99.999%
       sparc   4363333  100.000%
     sparc64   6751939  100.000%
      x86_64  19681173  100.000%
      xtensa         0         0

I think I'll commit this, but let's look at the original problem first as well.