On Tue, May 30, 2023 at 4:21 PM Jan Hubicka <[email protected]> wrote:
>
> > On Mon, May 29, 2023 at 6:20 PM Martin Jambor <[email protected]> wrote:
> > >
> > > Hi,
> > >
> > > there have been concerns that linear searches through DECL_ARGUMENTS
> > > that are often necessary to compute the index of a particular
> > > PARM_DECL which is the key to results of IPA-CP can happen often
> > > enough to be a compile time issue, especially if we plug the results
> > > into value numbering, as I intend to do with a follow-up patch.
> > >
> > > This patch creates a hash map to do the look-up for all functions
> > > which have some information discovered by IPA-CP and which have 32
> > > parameters or more. 32 is a hard-wired magical constant here to
> > > capture the trade-off between the memory allocation overhead and
> > > length of the linear search. I do not think it is worth making it a
> > > --param but if people think it appropriate, I can turn it into one.
> >
> > Since ipcp_transformation is short-lived (is it?) is it worth the trouble?
> > Comments below ...
>
> It lives from ipa-cp time to WPA stream-out or IPA transform stage,
> so memory consumption is a concern with -flto.
> > > + m_tree_to_idx = hash_map<const_tree, unsigned>::create_ggc (c);
> > > + unsigned index = 0;
> > > + for (tree p = DECL_ARGUMENTS (fndecl); p; p = DECL_CHAIN (p), index++)
> > > + m_tree_to_idx->put (p, index);
> >
> > I think allocating the hash-map with 'c' for some numbers (depending
> > on the "prime"
> > chosen) will necessarily cause re-allocation of the hash since we keep a
> > load
> > factor of at most 3/4 upon insertion.
> >
> > But - I wonder if a UID sorted array isn't a very much better data
> > structure for this?
> > That is, a vec<std::pair<int, unsigned> >?
>
> Yeah, I was thinking along this lines too.
> Having field directly in PARM_DECL node would be probably prettiest.
> In general this is probably not that important as wast amount of time we
> have few parameters and linear lookup is just fine.
There is 6 bits of DECL_OFFSET_ALIGN that could be re-purposed, but
64 parameters is a bit low. _Maybe_ PARM_DECL doesn't need any of
the tree_base bits so could use the full word for sth else as well ...
I also though it might be interesting to only record PARM_DECLs that
we have interesting info for and skip VARYING ones. So with an
indirection DECL_OFFSET_ALIGN -> index to non-varying param or
-1 the encoding space could shrink.
But still using a vec<> looks like a straight-forward improvement here.
Richard.
> Honza
> >
> > > +}
> > > diff --git a/gcc/ipa-prop.cc b/gcc/ipa-prop.cc
> > > index ab6de9f10da..f0976e363f7 100644
> > > --- a/gcc/ipa-prop.cc
> > > +++ b/gcc/ipa-prop.cc
> > > @@ -5776,16 +5776,9 @@ ipcp_get_parm_bits (tree parm, tree *value,
> > > widest_int *mask)
> > > if (!ts || vec_safe_length (ts->bits) == 0)
> > > return false;
> > >
> > > - int i = 0;
> > > - for (tree p = DECL_ARGUMENTS (current_function_decl);
> > > - p != parm; p = DECL_CHAIN (p))
> > > - {
> > > - i++;
> > > - /* Ignore static chain. */
> > > - if (!p)
> > > - return false;
> > > - }
> > > -
> > > + int i = ts->get_param_index (current_function_decl, parm);
> > > + if (i < 0)
> > > + return false;
> > > clone_info *cinfo = clone_info::get (cnode);
> > > if (cinfo && cinfo->param_adjustments)
> > > {
> > > @@ -5802,16 +5795,12 @@ ipcp_get_parm_bits (tree parm, tree *value,
> > > widest_int *mask)
> > > return true;
> > > }
> > >
> > > -
> > > -/* Update bits info of formal parameters as described in
> > > - ipcp_transformation. */
> > > +/* Update bits info of formal parameters of NODE as described in TS. */
> > >
> > > static void
> > > -ipcp_update_bits (struct cgraph_node *node)
> > > +ipcp_update_bits (struct cgraph_node *node, ipcp_transformation *ts)
> > > {
> > > - ipcp_transformation *ts = ipcp_get_transformation_summary (node);
> > > -
> > > - if (!ts || vec_safe_length (ts->bits) == 0)
> > > + if (vec_safe_is_empty (ts->bits))
> > > return;
> > > vec<ipa_bits *, va_gc> &bits = *ts->bits;
> > > unsigned count = bits.length ();
> > > @@ -5913,14 +5902,12 @@ ipcp_update_bits (struct cgraph_node *node)
> > > }
> > > }
> > >
> > > -/* Update value range of formal parameters as described in
> > > - ipcp_transformation. */
> > > +/* Update value range of formal parameters of NODE as described in TS.
> > > */
> > >
> > > static void
> > > -ipcp_update_vr (struct cgraph_node *node)
> > > +ipcp_update_vr (struct cgraph_node *node, ipcp_transformation *ts)
> > > {
> > > - ipcp_transformation *ts = ipcp_get_transformation_summary (node);
> > > - if (!ts || vec_safe_length (ts->m_vr) == 0)
> > > + if (vec_safe_is_empty (ts->m_vr))
> > > return;
> > > const vec<ipa_vr, va_gc> &vr = *ts->m_vr;
> > > unsigned count = vr.length ();
> > > @@ -5996,10 +5983,17 @@ ipcp_transform_function (struct cgraph_node *node)
> > > fprintf (dump_file, "Modification phase of node %s\n",
> > > node->dump_name ());
> > >
> > > - ipcp_update_bits (node);
> > > - ipcp_update_vr (node);
> > > ipcp_transformation *ts = ipcp_get_transformation_summary (node);
> > > - if (!ts || vec_safe_is_empty (ts->m_agg_values))
> > > + if (!ts
> > > + || (vec_safe_is_empty (ts->m_agg_values)
> > > + && vec_safe_is_empty (ts->bits)
> > > + && vec_safe_is_empty (ts->m_vr)))
> > > + return 0;
> > > +
> > > + ts->maybe_create_parm_idx_map (cfun->decl);
> > > + ipcp_update_bits (node, ts);
> > > + ipcp_update_vr (node, ts);
> > > + if (vec_safe_is_empty (ts->m_agg_values))
> > > return 0;
> > > param_count = count_formal_params (node->decl);
> > > if (param_count == 0)
> > > diff --git a/gcc/ipa-prop.h b/gcc/ipa-prop.h
> > > index f306f8a377e..211b12ff6b3 100644
> > > --- a/gcc/ipa-prop.h
> > > +++ b/gcc/ipa-prop.h
> > > @@ -925,16 +925,10 @@ ipa_is_param_used_by_polymorphic_call (class
> > > ipa_node_params *info, int i)
> > >
> > > struct GTY(()) ipcp_transformation
> > > {
> > > - /* Known aggregate values. */
> > > - vec<ipa_argagg_value, va_gc> *m_agg_values;
> > > - /* Known bits information. */
> > > - vec<ipa_bits *, va_gc> *bits;
> > > - /* Value range information. */
> > > - vec<ipa_vr, va_gc> *m_vr;
> > > -
> > > /* Default constructor. */
> > > ipcp_transformation ()
> > > - : m_agg_values (NULL), bits (NULL), m_vr (NULL)
> > > + : m_agg_values (nullptr), bits (nullptr), m_vr (nullptr),
> > > + m_tree_to_idx (nullptr)
> > > { }
> > >
> > > /* Default destructor. */
> > > @@ -944,6 +938,29 @@ struct GTY(()) ipcp_transformation
> > > vec_free (bits);
> > > vec_free (m_vr);
> > > }
> > > +
> > > + /* Given PARAM which must be a parameter of function FNDECL described
> > > by
> > > + THIS, return its index in the DECL_ARGUMENTS chain, using a
> > > pre-computed
> > > + hash map if avialable (which is pre-computed only if there are many
> > > + parameters). Can return -1 if param is static chain not
> > > represented among
> > > + DECL_ARGUMENTS. */
> > > + int get_param_index (const_tree fndecl, const_tree param) const;
> > > +
> > > + /* Assuming THIS describes FUNC and it has sufficiently many
> > > parameters to
> > > + justify the overhead, creat a has map from parameter trees to their
> > > + indices. */
> > > +
> > > + void maybe_create_parm_idx_map (tree fndecl);
> > > +
> > > + /* Known aggregate values. */
> > > + vec<ipa_argagg_value, va_gc> *m_agg_values;
> > > + /* Known bits information. */
> > > + vec<ipa_bits *, va_gc> *bits;
> > > + /* Value range information. */
> > > + vec<ipa_vr, va_gc> *m_vr;
> > > + /* If there are many parameters, a hash map to speed-up look-ups of
> > > their
> > > + indices. */
> > > + hash_map<const_tree, unsigned> *m_tree_to_idx;
> > > };
> > >
> > > inline
> > > --
> > > 2.40.1
> > >
