Problem cropping up in Value Range Propogation

[Gary Oblock via Gcc]

I'm trying to debug a problem cropping up in value range propagation.
Ironically I probably own an original copy 1995 copy of the paper it's
based on but that's not going to be much help since I'm lost in the
weeds.  It's running on some optimization (my structure reorg
optimization) generated GIMPLE statements.

Here's the GIMPLE dump:

Function max_of_y (max_of_y, funcdef_no=1, decl_uid=4391, cgraph_uid=2, 
symbol_order=20) (executed once)

max_of_y (unsigned long data, size_t len)
{
  double value;
  double result;
  size_t i;

  <bb 2> [local count: 118111600]:
  field_arry_addr_14 = _reorg_base_var_type_t.y;
  index_15 = (sizetype) data_27(D);
  offset_16 = index_15 * 8;
  field_addr_17 = field_arry_addr_14 + offset_16;
  field_val_temp_13 = MEM <double> [(void *)field_addr_17];
  result_8 = field_val_temp_13;
  goto <bb 6>; [100.00%]

  <bb 3> [local count: 955630225]:
  _1 = i_3 * 16;
  PPI_rhs1_cast_18 = (unsigned long) data_27(D);
  PPI_rhs2_cast_19 = (unsigned long) _1;
  PtrPlusInt_Adj_20 = PPI_rhs2_cast_19 / 16;
  PtrPlusInt_21 = PPI_rhs1_cast_18 + PtrPlusInt_Adj_20;
  dedangled_27 = (unsigned long) PtrPlusInt_21;
  field_arry_addr_23 = _reorg_base_var_type_t.y;
  index_24 = (sizetype) dedangled_27;
  offset_25 = index_24 * 8;
  field_addr_26 = field_arry_addr_23 + offset_25;
  field_val_temp_22 = MEM <double> [(void *)field_addr_26];
  value_11 = field_val_temp_22;
  if (result_5 < value_11)
    goto <bb 4>; [50.00%]
  else
    goto <bb 5>; [50.00%]

  <bb 4> [local count: 477815112]:

  <bb 5> [local count: 955630225]:
  # result_4 = PHI <result_5(3), value_11(4)>
  i_12 = i_3 + 1;

  <bb 6> [local count: 1073741824]:
  # i_3 = PHI <1(2), i_12(5)>
  # result_5 = PHI <result_8(2), result_4(5)>
  if (i_3 < len_9(D))
    goto <bb 3>; [89.00%]
  else
    goto <bb 7>; [11.00%]

  <bb 7> [local count: 118111600]:
  # result_10 = PHI <result_5(6)>
  return result_10;
}

The failure in VRP is occurring on

offset_16 = data_27(D) * 8;

which is the from two adjacent statements above

  index_15 = (sizetype) data_27(D);
  offset_16 = index_15 * 8;

being merged together.

Note, the types of index_15/16 are sizetype and data_27 is unsigned
long.
The error message is:

internal compiler error: tree check: expected class ‘type’, have ‘exceptional’ 
(error_mark) in to_wide,

Things only start to look broken in value_range::lower_bound in
value-range.cc when

return wi::to_wide (t);

is passed error_mark_node in t. It's getting it from m_min just above.
My observation is that m_min is not always error_mark_node. In fact, I
seem to think you need to use set_varying to get this to even happen.

Note, the ssa_propagation_engine processed the statement "offset_16 =
data..."  multiple times before failing on it. What oh what is
happening and how in the heck did I cause it???

Please, somebody throw me a life preserver on this.

Thanks,

Gary


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