[Bug bootstrap/80887] gnat bootstrap fails at s-regpat.o: raised STORAGE_ERROR : stack overflow or erroneous memory access

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80887

--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> ---
Seems to me that it is FRE valueization doing something strange. We have (not
in a loop)

  _26 = CHAIN.23_25(D)->parse_pos;
  _28 = _26 + 1;
  CHAIN.23_25(D)->parse_pos = _28;
  _30 = CHAIN.23_25(D)->expression;
  _32 = _30->P_ARRAY;
  _33 = CHAIN.23_25(D)->parse_pos;
  parse_pos.11_2 = (sizetype) _33;
  _3 = parse_pos.11_2 + 4294967295;

and when, during the simplification of some later stmt that turns out to be
equivalent to _3, we call vn_nary_op_lookup_pieces on _26 (with a NOP to
sizetype), it returns _3, so obviously we loop.