Re: RFC: peephole vs RTX_FRAME_RELATED_P

[Ian Lance Taylor <ian at airs dot com>]

Andrew Haley <aph@redhat.com> writes:

> The problem that is bugging me is if there is more than one
> instruction in the repleacement sequence, which one do you copy the
> REG_FRAME_RELATED_EXPR to?

I think an algorithm which should work fairly reliably in the general
case is:

  1) Are there any old insns with RTX_FRAME_RELATED_P set?
     If no, stop.
  2) For each old insn with RTX_FRAME_RELATED_P set:
     a) if insn has a REG_FRAME_RELATED_EXPR note, add it to the list;
     b) otherwise, insn should be a PARALLEL or SEQUENCE or SET;
        add the insn to the list.
  3) Set RTX_FRAME_RELATED_P on last new insn.
  4) If there is more than one entry on list, turn it into a PARALLEL
     (see dwarf2out_frame_debug_expr).  Otherwise take first insn on
     list.
  5) Put the result of 4 in a REG_FRAME_RELATED_EXPR note on last new
     insn.

Ian