[Bug target/114224] popcount RTL cost seems wrong with cssc

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114224

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
This is a matter of rtl costs.
.POPCOUNT expansion in expand_POPCOUNT expands the sequence both ways and asks
the backend what is cheaper:
  /* If .POPCOUNT call has 2 arguments, match_single_bit_test marked it
     because the result is only used in an equality comparison against 1.
     Use rtx costs in that case to determine if .POPCOUNT (arg) == 1
     or (arg ^ (arg - 1)) > arg - 1 is cheaper.
     If .POPCOUNT second argument is 0, we additionally know that arg
     is non-zero, so use arg & (arg - 1) == 0 instead.  */