[DF] Replace various bitmaps with HARD_REG_SETs

[Paolo Bonzini]

On Sat, Jul 30, 2011 at 19:08, Jakub Jelinek <jakub@redhat.com> wrote:
> And for bigger HARD_REG_SET, making it a struct would mean that all
> functions that use HARD_REG_SET in a read-only way and thus are passed
> a HARD_REG_SET argument rather than HARD_REG_SET * suddenly copy the whole
> bitset

The fix could be to add an IPA pass that changes pass-by-value to
pass-by-reference when possible.

Paolo