Hello,
On Wed, May 31 2023, Richard Biener wrote:
> On Tue, May 30, 2023 at 4:21 PM Jan Hubicka <hubi...@ucw.cz> wrote:
>>
>> > On Mon, May 29, 2023 at 6:20 PM Martin Jambor <mjam...@suse.cz> 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.
It lives longer, until the function is finished, it holds the
information we want to use during PRE, after all (and Honza also already
added queries to it to tree-ssa-ccp.cc though those probably could be
avoided).
The proposed mapping for long chains would only be created in the
transformation IPA-CP hook, so would only live in LTRANS and only
throughout the compilation of a single function. (But I am adding a
pointer to the transformation summary of all.)
>> > > + 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.
Oh, right.
>> >
>> > 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.
Yeah, 64 parameters seems too tight. I guess a testcase in which we
would record information for that many parameters would be quite
artificial, but I can imagine something like that in machine generated
code.
Below is the patch based on DECL_UIDs in a vector. The problem with
std::pair is that it is not GC-friendly and the transformation summary
unfortunately needs to live in GC. So I added a simple GTY marked
structure.
Bootstrapped, tested and (together with the subsequent patch) LTO
bootstrapped on an x86_64-linux, as is and with lower threshold to
create the mapping. OK for master now?
Thanks,
Martin
Subject: [PATCH 1/2] ipa-cp: Avoid long linear searches through DECL_ARGUMENTS
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 vector sorted according to PARM_DECLs 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.
gcc/ChangeLog:
2023-05-31 Martin Jambor <mjam...@suse.cz>
* ipa-prop.h (ipa_uid_to_idx_map_elt): New type.
(struct ipcp_transformation): Rearrange members according to
C++ class coding convention, add m_uid_to_idx,
get_param_index and maybe_create_parm_idx_map.
* ipa-cp.cc (ipcp_transformation::get_param_index): New function.
(compare_uids): Likewise.
(ipcp_transformation::maype_create_parm_idx_map): Likewise.
* ipa-prop.cc (ipcp_get_parm_bits): Use get_param_index.
(ipcp_update_bits): Accept TS as a parameter, assume it is not NULL.
(ipcp_update_vr): Likewise.
(ipcp_transform_function): Call, maybe_create_parm_idx_map of TS, bail
out quickly if empty, pass it to ipcp_update_bits and ipcp_update_vr.
---
gcc/ipa-cp.cc | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
gcc/ipa-prop.cc | 44 +++++++++++++---------------
gcc/ipa-prop.h | 44 ++++++++++++++++++++++------
3 files changed, 131 insertions(+), 33 deletions(-)
diff --git a/gcc/ipa-cp.cc b/gcc/ipa-cp.cc
index 0f37bb5e336..fb069bf2319 100644
--- a/gcc/ipa-cp.cc
+++ b/gcc/ipa-cp.cc
@@ -6761,3 +6761,79 @@ ipa_cp_cc_finalize (void)
orig_overall_size = 0;
ipcp_free_transformation_sum ();
}
+
+/* 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
+ DECL_UID-sorted vector if available (which is pre-computed only if there are
+ many parameters). Can return -1 if param is static chain not represented
+ among DECL_ARGUMENTS. */
+
+int
+ipcp_transformation::get_param_index (const_tree fndecl, const_tree param)
const
+{
+ gcc_assert (TREE_CODE (param) == PARM_DECL);
+ if (m_uid_to_idx)
+ {
+ unsigned puid = DECL_UID (param);
+ const ipa_uid_to_idx_map_elt *res
+ = std::lower_bound (m_uid_to_idx->begin(), m_uid_to_idx->end (), puid,
+ [] (const ipa_uid_to_idx_map_elt &elt, unsigned uid)
+ {
+ return elt.uid < uid;
+ });
+ if (res == m_uid_to_idx->end ()
+ || res->uid != puid)
+ {
+ gcc_assert (DECL_STATIC_CHAIN (fndecl));
+ return -1;
+ }
+ return res->index;
+ }
+
+ unsigned index = 0;
+ for (tree p = DECL_ARGUMENTS (fndecl); p; p = DECL_CHAIN (p), index++)
+ if (p == param)
+ return (int) index;
+
+ gcc_assert (DECL_STATIC_CHAIN (fndecl));
+ return -1;
+}
+
+/* Helper function to qsort a vector of ipa_uid_to_idx_map_elt elements
+ according to the uid. */
+
+static int
+compare_uids (const void *a, const void *b)
+{
+ const ipa_uid_to_idx_map_elt *e1 = (const ipa_uid_to_idx_map_elt *) a;
+ const ipa_uid_to_idx_map_elt *e2 = (const ipa_uid_to_idx_map_elt *) b;
+ if (e1->uid < e2->uid)
+ return -1;
+ if (e1->uid > e2->uid)
+ return 1;
+ gcc_unreachable ();
+}
+
+/* Assuming THIS describes FNDECL and it has sufficiently many parameters to
+ justify the overhead, create a DECL_UID-sorted vector to speed up mapping
+ from parameters to their indices in DECL_ARGUMENTS chain. */
+
+void
+ipcp_transformation::maybe_create_parm_idx_map (tree fndecl)
+{
+ int c = count_formal_params (fndecl);
+ if (c < 32)
+ return;
+
+ m_uid_to_idx = NULL;
+ vec_safe_reserve (m_uid_to_idx, c, true);
+ unsigned index = 0;
+ for (tree p = DECL_ARGUMENTS (fndecl); p; p = DECL_CHAIN (p), index++)
+ {
+ ipa_uid_to_idx_map_elt elt;
+ elt.uid = DECL_UID (p);
+ elt.index = index;
+ m_uid_to_idx->quick_push (elt);
+ }
+ m_uid_to_idx->qsort (compare_uids);
+}
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..c570e8ec25a 100644
--- a/gcc/ipa-prop.h
+++ b/gcc/ipa-prop.h
@@ -921,20 +921,24 @@ ipa_is_param_used_by_polymorphic_call (class
ipa_node_params *info, int i)
return (*info->descriptors)[i].used_by_polymorphic_call;
}
+/* GTY-marked structure used to map DECL_UIDs of APRAMs to their indices in
+ their DECL_ARGUMENTs chain. */
+struct GTY(()) ipa_uid_to_idx_map_elt
+{
+ /* DECL_UID of the PARAM. */
+ unsigned uid;
+ /* Its index in the DECL_ARGUMETs chain. */
+ unsigned index;
+};
+
/* Structure holding information for the transformation phase of IPA-CP. */
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_uid_to_idx (nullptr)
{ }
/* Default destructor. */
@@ -944,6 +948,30 @@ 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
+ DECL_UID-sorted vector if available (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 FNDECL and it has sufficiently many parameters to
+ justify the overhead, create a DECL_UID-sorted vector to speed up mapping
+ from parameters to their indices in DECL_ARGUMENTS chain. */
+
+ 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, this is a vector sorted by their DECL_UIDs
+ to map them to their indices in the DECL_ARGUMENT chain. */
+ vec<ipa_uid_to_idx_map_elt, va_gc> *m_uid_to_idx;
};
inline
--
2.40.1
