Re: [RFC][IPA-VRP] Add support for IPA VRP in ipa-cp/ipa-prop

[Jan Hubicka <hubicka@ucw.cz>]

> Maybe it is better to separate value range and alignment summary
> writing/reading to different functions. Here is another updated
> version which does this.

Makes sense to me. Note that the alignment summary propagation can be either
handled by doing bitwise constant propagation and/or extending our value ranges
by stride (as described in
http://www.lighterra.com/papers/valuerangeprop/Patterson1995-ValueRangeProp.pdf
I would like it to go eventually away in favour of more generic solution.

> -/* If DEST_PLATS already has aggregate items, check that aggs_by_ref matches
> +/* Propagate value range across jump function JFUNC that is associated with
> +   edge CS and update DEST_PLATS accordingly.  */
> +
> +static bool
> +propagate_vr_accross_jump_function (cgraph_edge *cs,
> +				    ipa_jump_func *jfunc,
> +				    struct ipcp_param_lattices *dest_plats)
> +{
> +  struct ipcp_param_lattices *src_lats;
> +  ipcp_vr_lattice *dest_lat = &dest_plats->m_value_range;
> +
> +  if (dest_lat->bottom_p ())
> +    return false;
> +
> +  if (jfunc->type == IPA_JF_PASS_THROUGH)
> +    {
> +      struct ipa_node_params *caller_info = IPA_NODE_REF (cs->caller);
> +      int src_idx = ipa_get_jf_pass_through_formal_id (jfunc);
> +      src_lats = ipa_get_parm_lattices (caller_info, src_idx);
> +
> +      if (ipa_get_jf_pass_through_operation (jfunc) == NOP_EXPR)
> +	return dest_lat->meet_with (src_lats->m_value_range);

Clearly we can propagate thorugh expressions here (PLUS_EXPR). I have run
into similar issue in loop code that builds simple generic expresisons
(like (int)ssa_name+10) and it would be nice to have easy way to deterine
their value range based on the knowledge of SSA_NAME's valur range.

Bit this is fine for initial implementaiotn for sure.
>  
> +/* Look up all VR information that we have discovered and copy it over
> +   to the transformation summary.  */
> +
> +static void
> +ipcp_store_vr_results (void)
> +{
> +  cgraph_node *node;
> +
> +  FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (node)
> +  {
> +    ipa_node_params *info = IPA_NODE_REF (node);
> +    bool found_useful_result = false;
> +
> +    if (!opt_for_fn (node->decl, flag_ipa_vrp))
> +      {
> +	if (dump_file)
> +	  fprintf (dump_file, "Not considering %s for VR discovery "
> +		   "and propagate; -fipa-ipa-vrp: disabled.\n",
> +		   node->name ());
> +	continue;

I belive you need to also prevent propagation through functions copmiled with
-fno-ipa-vrp, not only prevent any transformations.
> +/* Update value range of formal parameters as described in
> +   ipcp_transformation_summary.  */
> +
> +static void
> +ipcp_update_vr (struct cgraph_node *node)
> +{
> +  tree fndecl = node->decl;
> +  tree parm = DECL_ARGUMENTS (fndecl);
> +  tree next_parm = parm;
> +  ipcp_transformation_summary *ts = ipcp_get_transformation_summary (node);
> +  if (!ts || vec_safe_length (ts->m_vr) == 0)
> +    return;
> +  const vec<ipa_vr, va_gc> &vr = *ts->m_vr;
> +  unsigned count = vr.length ();
> +
> +  for (unsigned i = 0; i < count; ++i, parm = next_parm)
> +    {
> +      if (node->clone.combined_args_to_skip
> +	  && bitmap_bit_p (node->clone.combined_args_to_skip, i))
> +	continue;
> +      gcc_checking_assert (parm);
> +      next_parm = DECL_CHAIN (parm);
> +      tree ddef = ssa_default_def (DECL_STRUCT_FUNCTION (node->decl), parm);
> +
> +      if (!ddef || !is_gimple_reg (parm))
> +	continue;
> +
> +      if (cgraph_local_p (node)
The test of cgraph_local_p seems redundant here. The analysis phase should not determine
anything if function is reachable non-locally.
> +/* Info about value ranges.  */
> +
> +struct GTY(()) ipa_vr
> +{
> +  /* The data fields below are valid only if known is true.  */
> +  bool known;
> +  enum value_range_type type;
> +  tree min;
> +  tree max;
What is the point of representing range as trees rather than wide ints. Can they
be non-constant integer?

The patch looks good to me otherwise!
Honza