Re: [PATCH 2/2] ipa-cp: Feed results of IPA-CP into value numbering

[Martin Jambor <mjambor@suse.cz>]

Hello Richi,

it took me quite time to get back to this but it might have actually
helped because it forced me to re-read the code around and in turn
simplify the patch.

On Mon, Jun 12 2023, Richard Biener wrote:
> On Fri, 9 Jun 2023, Martin Jambor wrote:
>

[...]

>> @@ -2327,7 +2330,7 @@ vn_walk_cb_data::push_partial_def (pd_data pd,
>>     with the current VUSE and performs the expression lookup.  */
>>  
>>  static void *
>> -vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse, void *data_)
>> +vn_reference_lookup_2 (ao_ref *op, tree vuse, void *data_)
>>  {
>>    vn_walk_cb_data *data = (vn_walk_cb_data *)data_;
>>    vn_reference_t vr = data->vr;
>> @@ -2361,6 +2364,38 @@ vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse, void *data_)
>>        return *slot;
>>      }
>>  
>> +  if (SSA_NAME_IS_DEFAULT_DEF (vuse)
>          && data->partial_defs.is_empty ())
>
> ^^ do this check early

The check is actually done right at the beginning of the function
already so I simply removed it.

>
>> +    {
>> +      HOST_WIDE_INT offset, size;
>> +      tree v = NULL_TREE;
>          tree base = ao_ref_base (op);
>          if ((TREE_CODE (base) == PARM_DECL
>               || TREE_CODE (base) == MEM_REF)
>
> handle both kind of bases with ...
>
>> +	  && op->offset.is_constant (&offset)
>> +	  && op->size.is_constant (&size)
>> +	  && op->max_size_known_p ()
>> +	  && known_eq (op->size, op->max_size))
>
> ^^^ this preconditions (would have been missing in the MEM_REF branch
> before)

I missed that call to ao_ref_base fills in these fields - and in the
pointer case that they are not filled in without it.  I hope the patch
below is the simplified version you wanted.

The patch passed bootstrap and testing and also LTO bootstrap on
x86_64-linux.

Thanks,

Martin



PRs 68930 and 92497 show that when IPA-CP figures out constants in
aggregate parameters or when passed by reference but the loads happen
in an inlined function the information is lost.  This happens even
when the inlined function itself was known to have - or even cloned to
have - such constants in incoming parameters because the transform
phase of IPA passes is not run on them.  See discussion in the bugs
for reasons why.

Honza suggested that we can plug the results of IPA-CP analysis into
value numbering, so that FRE can figure out that some loads fetch
known constants.  This is what this patch attempts to do.  The patch
does not attempt to populate partial_defs with information from
IPA-CP, this can be hopefully added as a follow-up.

gcc/ChangeLog:

2023-08-11  Martin Jambor  <mjambor@suse.cz>

	PR ipa/68930
	PR ipa/92497
	* ipa-prop.h (ipcp_get_aggregate_const): Declare.
	* ipa-prop.cc (ipcp_get_aggregate_const): New function.
	(ipcp_transform_function): Do not deallocate transformation info.
	* tree-ssa-sccvn.cc: Include alloc-pool.h, symbol-summary.h and
	ipa-prop.h.
	(vn_reference_lookup_2): When hitting default-def vuse, query
	IPA-CP transformation info for any known constants.

gcc/testsuite/ChangeLog:

2023-06-07  Martin Jambor  <mjambor@suse.cz>

	PR ipa/68930
	PR ipa/92497
	* gcc.dg/ipa/pr92497-1.c: New test.
	* gcc.dg/ipa/pr92497-2.c: Likewise.
---
 gcc/ipa-prop.cc                      | 33 +++++++++++++++++++++++----
 gcc/ipa-prop.h                       |  3 +++
 gcc/testsuite/gcc.dg/ipa/pr92497-1.c | 26 +++++++++++++++++++++
 gcc/testsuite/gcc.dg/ipa/pr92497-2.c | 26 +++++++++++++++++++++
 gcc/tree-ssa-sccvn.cc                | 34 +++++++++++++++++++++++++++-
 5 files changed, 116 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/ipa/pr92497-1.c
 create mode 100644 gcc/testsuite/gcc.dg/ipa/pr92497-2.c

diff --git a/gcc/ipa-prop.cc b/gcc/ipa-prop.cc
index 4f6ed7b89bd..9efaa5cb848 100644
--- a/gcc/ipa-prop.cc
+++ b/gcc/ipa-prop.cc
@@ -5760,6 +5760,34 @@ ipcp_modif_dom_walker::before_dom_children (basic_block bb)
   return NULL;
 }
 
+/* If IPA-CP discovered a constant in parameter PARM at OFFSET of a given SIZE
+   - whether passed by reference or not is given by BY_REF - return that
+   constant.  Otherwise return NULL_TREE.  */
+
+tree
+ipcp_get_aggregate_const (struct function *func, tree parm, bool by_ref,
+			  HOST_WIDE_INT bit_offset, HOST_WIDE_INT bit_size)
+{
+  cgraph_node *node = cgraph_node::get (func->decl);
+  ipcp_transformation *ts = ipcp_get_transformation_summary (node);
+
+  if (!ts || !ts->m_agg_values)
+    return NULL_TREE;
+
+  int index = ts->get_param_index (func->decl, parm);
+  if (index < 0)
+    return NULL_TREE;
+
+  ipa_argagg_value_list avl (ts);
+  unsigned unit_offset = bit_offset / BITS_PER_UNIT;
+  tree v = avl.get_value (index, unit_offset, by_ref);
+  if (!v
+      || maybe_ne (tree_to_poly_int64 (TYPE_SIZE (TREE_TYPE (v))), bit_size))
+    return NULL_TREE;
+
+  return v;
+}
+
 /* Return true if we have recorded VALUE and MASK about PARM.
    Set VALUE and MASk accordingly.  */
 
@@ -6031,11 +6059,6 @@ ipcp_transform_function (struct cgraph_node *node)
     free_ipa_bb_info (bi);
   fbi.bb_infos.release ();
 
-  ipcp_transformation *s = ipcp_transformation_sum->get (node);
-  s->m_agg_values = NULL;
-  s->bits = NULL;
-  s->m_vr = NULL;
-
   vec_free (descriptors);
   if (cfg_changed)
     delete_unreachable_blocks_update_callgraph (node, false);
diff --git a/gcc/ipa-prop.h b/gcc/ipa-prop.h
index 410c951a256..7e033d2a7b8 100644
--- a/gcc/ipa-prop.h
+++ b/gcc/ipa-prop.h
@@ -1235,6 +1235,9 @@ void ipa_dump_param (FILE *, class ipa_node_params *info, int i);
 void ipa_release_body_info (struct ipa_func_body_info *);
 tree ipa_get_callee_param_type (struct cgraph_edge *e, int i);
 bool ipcp_get_parm_bits (tree, tree *, widest_int *);
+tree ipcp_get_aggregate_const (struct function *func, tree parm, bool by_ref,
+			       HOST_WIDE_INT bit_offset,
+			       HOST_WIDE_INT bit_size);
 bool unadjusted_ptr_and_unit_offset (tree op, tree *ret,
 				     poly_int64 *offset_ret);
 
diff --git a/gcc/testsuite/gcc.dg/ipa/pr92497-1.c b/gcc/testsuite/gcc.dg/ipa/pr92497-1.c
new file mode 100644
index 00000000000..dcece15963c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/pr92497-1.c
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fno-early-inlining"  } */
+
+struct a {int a;};
+static int
+foo (struct a a)
+{
+  if (!__builtin_constant_p (a.a))
+    __builtin_abort ();
+  return a.a;
+}
+
+static int __attribute__ ((noinline))
+bar (struct a a)
+{
+  return foo(a);
+}
+
+volatile int r;
+
+int main()
+{
+  struct a a={1};
+  r = bar (a);
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/ipa/pr92497-2.c b/gcc/testsuite/gcc.dg/ipa/pr92497-2.c
new file mode 100644
index 00000000000..c64090d1a7a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/pr92497-2.c
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fno-early-inlining -fno-ipa-sra"  } */
+
+struct a {int a;};
+static int
+foo (struct a *a)
+{
+  if (!__builtin_constant_p (a->a))
+    __builtin_abort ();
+  return a->a;
+}
+
+static int __attribute__ ((noinline))
+bar (struct a *a)
+{
+  return foo(a);
+}
+
+volatile int r;
+
+int main()
+{
+  struct a a={1};
+  r = bar (&a);
+  return 0;
+}
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index 32e06fae3b9..b1678911671 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -74,6 +74,9 @@ along with GCC; see the file COPYING3.  If not see
 #include "ipa-modref-tree.h"
 #include "ipa-modref.h"
 #include "tree-ssa-sccvn.h"
+#include "alloc-pool.h"
+#include "symbol-summary.h"
+#include "ipa-prop.h"
 
 /* This algorithm is based on the SCC algorithm presented by Keith
    Cooper and L. Taylor Simpson in "SCC-Based Value numbering"
@@ -2327,7 +2330,7 @@ vn_walk_cb_data::push_partial_def (pd_data pd,
    with the current VUSE and performs the expression lookup.  */
 
 static void *
-vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse, void *data_)
+vn_reference_lookup_2 (ao_ref *op, tree vuse, void *data_)
 {
   vn_walk_cb_data *data = (vn_walk_cb_data *)data_;
   vn_reference_t vr = data->vr;
@@ -2361,6 +2364,35 @@ vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse, void *data_)
       return *slot;
     }
 
+  if (SSA_NAME_IS_DEFAULT_DEF (vuse))
+    {
+      HOST_WIDE_INT op_offset, op_size;
+      tree v = NULL_TREE;
+      tree base = ao_ref_base (op);
+
+      if (base
+	  && op->offset.is_constant (&op_offset)
+	  && op->size.is_constant (&op_size)
+	  && op->max_size_known_p ()
+	  && known_eq (op->size, op->max_size))
+	{
+	  if (TREE_CODE (base) == PARM_DECL)
+	    v = ipcp_get_aggregate_const (cfun, base, false, op_offset,
+					  op_size);
+	  else if (TREE_CODE (base) == MEM_REF
+		   && integer_zerop (TREE_OPERAND (base, 1))
+		   && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME
+		   && SSA_NAME_IS_DEFAULT_DEF (TREE_OPERAND (base, 0))
+		   && (TREE_CODE (SSA_NAME_VAR (TREE_OPERAND (base, 0)))
+		       == PARM_DECL))
+	    v = ipcp_get_aggregate_const (cfun,
+					  SSA_NAME_VAR (TREE_OPERAND (base, 0)),
+					  true, op_offset, op_size);
+	}
+      if (v)
+	return data->finish (vr->set, vr->base_set, v);
+    }
+
   return NULL;
 }
 
-- 
2.41.0