Re: [RFC] Bug lto/78140

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Jan 30, 2017 at 12:23 AM, kugan
<kugan.vivekanandarajah@linaro.org> wrote:
> Hi All,
>
> As suggested by Richard in the PR, I tried to implement variable size
> structures for VR as shown in attached patch. That is, I changed ipa-prop.h
> to:
>
> diff --git a/gcc/ipa-prop.h b/gcc/ipa-prop.h
> index 93a2390c..acab2aa 100644
> --- a/gcc/ipa-prop.h
> +++ b/gcc/ipa-prop.h
> @@ -157,13 +157,15 @@ struct GTY(()) ipa_bits
>  };
>
>  /* Info about value ranges.  */
> -struct GTY(()) ipa_vr
> +struct GTY ((variable_size)) ipa_vr
>  {
>    /* The data fields below are valid only if known is true.  */
>    bool known;
>    enum value_range_type type;
> -  wide_int min;
> -  wide_int max;
> +  /* Minimum and maximum.  */
> +  TRAILING_WIDE_INT_ACCESSOR (min, ints, 0)
> +  TRAILING_WIDE_INT_ACCESSOR (max, ints, 1)
> +  trailing_wide_ints <2> ints;
>  };
>
>  /* A jump function for a callsite represents the values passed as actual
> @@ -525,7 +527,7 @@ struct GTY(()) ipcp_transformation_summary
>    /* Known bits information.  */
>    vec<ipa_bits, va_gc> *bits;
>    /* Value range information.  */
> -  vec<ipa_vr, va_gc> *m_vr;
> +  vec<ipa_vr *, va_gc> *m_vr;
>  };
>
>  void ipa_set_node_agg_value_chain (struct cgraph_node *node,
>
> However, I am running into error when I do LTO bootstrap that memory seems
> to have deallocated by the garbage collector. Since we have the reference to
> the memory allocated by ggc_internal_alloc in the vector (m_vr), I thought
> it will not be deallocated. But during the bootstrap, when in
> ipa_node_params_t::duplicate, it seems to have been deallocated as shown in
> the back trace. I dont understand internals of gc in gcc so any help is
> appreciated.
>
>
> lto1: internal compiler error: Segmentation fault
> 0xdedc4b crash_signal
>         ../../gcc/gcc/toplev.c:333
> 0xb46680 ipa_node_params_t::duplicate(cgraph_node*, cgraph_node*,
> ipa_node_params*, ipa_node_params*)
>         ../../gcc/gcc/ipa-prop.c:3819
> 0xb306a3
> function_summary<ipa_node_params*>::symtab_duplication(cgraph_node*,
> cgraph_node*, void*)
>         ../../gcc/gcc/symbol-summary.h:187
> 0x85aba7 symbol_table::call_cgraph_duplication_hooks(cgraph_node*,
> cgraph_node*)
>         ../../gcc/gcc/cgraph.c:488
> 0x8765bf cgraph_node::create_clone(tree_node*, long, int, bool,
> vec<cgraph_edge*, va_heap, vl_ptr>, bool, cgraph_node*, bitmap_head*, char
> const*)
>         ../../gcc/gcc/cgraphclones.c:522
> 0x166fb3b clone_inlined_nodes(cgraph_edge*, bool, bool, int*, int)
>         ../../gcc/gcc/ipa-inline-transform.c:227
> 0x166fbd7 clone_inlined_nodes(cgraph_edge*, bool, bool, int*, int)
>         ../../gcc/gcc/ipa-inline-transform.c:242
> 0x1670893 inline_call(cgraph_edge*, bool, vec<cgraph_edge*, va_heap,
> vl_ptr>*, int*, bool, bool*)
>         ../../gcc/gcc/ipa-inline-transform.c:449
> 0x1665bd3 inline_small_functions
>         ../../gcc/gcc/ipa-inline.c:2024
> 0x1667157 ipa_inline
>         ../../gcc/gcc/ipa-inline.c:2434
> 0x1667fa7 execute
>         ../../gcc/gcc/ipa-inline.c:2845
>
>
> I tried similar think without variable structure like:
> diff --git a/gcc/ipa-prop.h b/gcc/ipa-prop.h
> index 93a2390c..b0cc832 100644
> --- a/gcc/ipa-prop.h
> +++ b/gcc/ipa-prop.h
> @@ -525,7 +525,7 @@ struct GTY(()) ipcp_transformation_summary
>    /* Known bits information.  */
>    vec<ipa_bits, va_gc> *bits;
>    /* Value range information.  */
> -  vec<ipa_vr, va_gc> *m_vr;
> +  vec<ipa_vr *, va_gc> *m_vr;
>  };
>
> This also has the same issue so I don't think it has anything to do with
> variable structure.

You have to debug that detail yourself but I wonder why the transformation
summary has a different representation than the jump function (and I think
the jump function size is the issue).

The JF has

  /* Information about zero/non-zero bits.  */
  struct ipa_bits bits;

  /* Information about value range, containing valid data only when vr_known is
     true.  */
  value_range m_vr;
  bool vr_known;

with ipa_bits having two widest_ints and value_range having two trees
and an unused bitmap and ipa_vr having two wide_ints (widest_ints are
smaller!).

Richard.

>
> Thanks,
> Kugan