Re: [PATCH, LRA] Remove REG_DEAD and REG_UNUSED notes.

[Eric Botcazou]

> > The description is too terse.  In the RTL middle-end, you shouldn't have
> > to manually deal with the REG_DEAD and REG_UNUSED notes (unlike
> > REG_EQUAL and REG_EQUIV notes), as the DF framework is supposed to do
> > it for you.
>
> Unfortunately LRA uses its own DF framework.

In fact reload does just the same:

  /* Make a pass over all the insns and delete all USEs which we inserted
     only to tag a REG_EQUAL note on them.  Remove all REG_DEAD and REG_UNUSED
     notes.  Delete all CLOBBER insns, except those that refer to the return
     value and the special mem:BLK CLOBBERs added to prevent the scheduler
     from misarranging variable-array code, and simplify (subreg (reg))
     operands.  Strip and regenerate REG_INC notes that may have been moved
     around.  */

[...]

        pnote = &REG_NOTES (insn);
        while (*pnote != 0)
          {
            if (REG_NOTE_KIND (*pnote) == REG_DEAD
                || REG_NOTE_KIND (*pnote) == REG_UNUSED
                || REG_NOTE_KIND (*pnote) == REG_INC)
              *pnote = XEXP (*pnote, 1);
            else
              pnote = &XEXP (*pnote, 1);
          }

so I guess LRA is entitled to do it as well.  But the proper fix to this is to 
recompute the REG_DEAD/REG_UNUSED notes at the beginning of postreload.

-- 
Eric Botcazou