On Tue, Aug 11, 2020 at 6:15 AM Gary Oblock via Gcc <gcc@gcc.gnu.org> wrote:
>
> 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,
This means the SSA name looked at is released and should no longer be
refered from in the IL.
> 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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