[Bug ipa/78644] [7 Regression] ICE: SIGSEGV in is_gimple_reg_type with -Og -fipa-cp

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78644

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, before ccp4 we have:
  _7 = x3_1 + x2_3;
  _8 = {_7, _7, _7, _7};
  x4.1_9 = x4;
  _15 = {_7, _7, _7, _7};
  _16 = BIT_FIELD_REF <_15, 128, 0>;
  _17 = BIT_FIELD_REF <x4.1_9, 128, 0>;
  _18 = _16 + _17;
  _19 = {_7, _7, _7, _7};
  _20 = BIT_FIELD_REF <_19, 128, 128>;
  _21 = BIT_FIELD_REF <x4.1_9, 128, 128>;
  _22 = _20 + _21;
  _23 = {_7, _7, _7, _7};
  _24 = BIT_FIELD_REF <_23, 128, 256>;
  _25 = BIT_FIELD_REF <x4.1_9, 128, 256>;
  _26 = _24 + _25;
  _27 = {_7, _7, _7, _7};
  _28 = BIT_FIELD_REF <_27, 128, 384>;
  _29 = BIT_FIELD_REF <x4.1_9, 128, 384>;
  _30 = _28 + _29;
  _10 = {_18, _22, _26, _30};
  <retval> = _10;

ccp4 sees those uses:
_7 : -->20 uses.
_27 = {_7, _7, _7, _7};
_27 = {_7, _7, _7, _7};
_27 = {_7, _7, _7, _7};
_27 = {_7, _7, _7, _7};
_23 = {_7, _7, _7, _7};
_23 = {_7, _7, _7, _7};
_23 = {_7, _7, _7, _7};
_23 = {_7, _7, _7, _7};
_19 = {_7, _7, _7, _7};
_19 = {_7, _7, _7, _7};
_19 = {_7, _7, _7, _7};
_19 = {_7, _7, _7, _7};
_15 = {_7, _7, _7, _7};
_15 = {_7, _7, _7, _7};
_15 = {_7, _7, _7, _7};
_15 = {_7, _7, _7, _7};
_8 = {_7, _7, _7, _7};
_8 = {_7, _7, _7, _7};
_8 = {_7, _7, _7, _7};
_8 = {_7, _7, _7, _7};
...
Visiting statement:
_7 = x3_1 + x2_3;
which is likely CONSTANT
Match-and-simplified x3_1 + x2_3 to 0
Lattice value changed to CONSTANT 0.  Adding SSA edges to worklist.

and replaces all those ctors with {x2_3, x2_3, x2_3, x2_3}.
But folding also happens while this is ongoing:
Folding statement: _17 = BIT_FIELD_REF <x4.1_9, 128, 0>;
Not folded
Folding statement: _18 = _16 + _17;
Folded into: _18 = _7 + _17;
and thus a new _7 reference appears, and we don't fold that into _18 = x2_3 +
_17, but remove the _7 setter, because we assume all uses are replaced:

Removing dead stmt _7 = x3_1 + x2_3;

Richi, I think this is your area of expertise.