RFC: peephole vs RTX_FRAME_RELATED_P

Mon Dec 19 22:11:00 GMT 2005

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