Re: [PATCH] Fix for PR52009 - Another missed tail merging opportunity

[Tom de Vries <Tom_deVries at mentor dot com>]

On 31/01/12 22:07, Tom de Vries wrote:
> On 31/01/12 22:05, Tom de Vries wrote:
>> Richard,
>>
> 
> Sorry, with patch this time.
> 
>> this patch fixes PR52009.
>>
>> Consider this test-case:
>> ...
>> int z;
>>
>> void
>> foo (int y)
>> {
>>   if (y == 6)
>>     z = 5;
>>   else
>>     z = 5;
>> }
>> ...
>>
>> Currently, compiling with -O2 gives us this representation at pr51879-7.c.094t.pre:
>> ...
>>   # BLOCK 3 freq:1991
>>   # PRED: 2 [19.9%]  (true,exec)
>>   # .MEMD.1710_4 = VDEF <.MEMD.1710_3(D)>
>>   zD.1702 = 5;
>>   goto <bb 5>;
>>   # SUCC: 5 [100.0%]  (fallthru,exec)
>>
>>   # BLOCK 4 freq:8009
>>   # PRED: 2 [80.1%]  (false,exec)
>>   # .MEMD.1710_5 = VDEF <.MEMD.1710_3(D)>
>>   zD.1702 = 5;
>>   # SUCC: 5 [100.0%]  (fallthru,exec)
>>
>>   # BLOCK 5 freq:10000
>>   # PRED: 3 [100.0%]  (fallthru,exec) 4 [100.0%]  (fallthru,exec)
>>   # .MEMD.1710_2 = PHI <.MEMD.1710_4(3), .MEMD.1710_5(4)>
>>   # VUSE <.MEMD.1710_2>
>>   return;
>> ...
>>
>> Blocks 3 and 4 are not tail-merged.
>>
>> The patch allows the example to be tail-merged by:
>> - value numbering .MEMD.1710_4 and .MEMD.1710_5 equal
>> - comparing gimple_vdef value numbers for assignments during tail-merge
>>
>> Bootstrapped and reg-tested on x86_64.
>>
>> OK for stage1?
>>

Richard,

I did some trivial changes such that the patch is applicable again to trunk, and
added a test-case, which you suggested in
http://gcc.gnu.org/ml/gcc-patches/2012-05/msg00220.html.

The test-case handles the case of 2 identical calls assigning to different
deferenced pointers, where the pointers are value-numbered the same:
...
void bar (int c, int *p)
{
  int *q = p;

  if (c)
    *p = foo ();
  else
    *q = foo ();
}
...

The representation before pre looks like this:
...
  # BLOCK 3 freq:3900
  # PRED: 2 [39.0%]  (true,exec)
  # .MEMD.1724_8 = VDEF <.MEMD.1724_7(D)>
  # USE = nonlocal
  # CLB = nonlocal
  D.1721_4 = fooD.1712 ();
  # .MEMD.1724_9 = VDEF <.MEMD.1724_8>
  *pD.1714_1(D) = D.1721_4;
  goto <bb 5>;
  # SUCC: 5 [100.0%]  (fallthru,exec)

  # BLOCK 4 freq:6100
  # PRED: 2 [61.0%]  (false,exec)
  # .MEMD.1724_10 = VDEF <.MEMD.1724_7(D)>
  # USE = nonlocal
  # CLB = nonlocal
  D.1723_5 = fooD.1712 ();
  # .MEMD.1724_11 = VDEF <.MEMD.1724_10>
  *qD.1717_2 = D.1723_5;
  # SUCC: 5 [100.0%]  (fallthru,exec)
...

In pre, we're already value numbering the result and vdef of the calls the same,
and the pointers the same:
...
Value numbers:
q_2 = p_1(D)
D.1723_5 = D.1721_4
.MEM_10 = .MEM_8
...

But not the vdefs of the stores. This patch implements that, and allows the
blocks to be merged.

ok for trunk?

Thanks,
- Tom

2012-07-04  Tom de Vries  <tom@codesourcery.com>

	PR tree-optimization/52009
	* tree-ssa-tail-merge.c (gimple_equal_p): For GIMPLE_ASSIGN, compare
	value numbers of gimple_vdef.
	* tree-ssa-sccvn.h (vn_reference_insert): Add vdef parameter to
	prototype.
	* tree-ssa-sccvn.c (copy_reference_ops_from_ref): Handle MODIFY_EXPR.
	(vn_reference_insert): Add and handle vdef parameter.
	(visit_reference_op_load): Add argument to vn_reference_insert call.
	(visit_reference_op_store): Find value number of vdef of store.  Insert
	value number of vdef of store.

	* gcc.dg/pr51879-7.c: New test.
	* gcc.dg/pr51879-18.c: New test.

Index: gcc/tree-ssa-tail-merge.c
===================================================================
--- gcc/tree-ssa-tail-merge.c (revision 189007)
+++ gcc/tree-ssa-tail-merge.c (working copy)
@@ -1119,6 +1119,14 @@ gimple_equal_p (same_succ same_succ, gim
     case GIMPLE_ASSIGN:
       lhs1 = gimple_get_lhs (s1);
       lhs2 = gimple_get_lhs (s2);
+      if (gimple_vdef (s1))
+	{
+	  if (vn_valueize (gimple_vdef (s1)) != vn_valueize (gimple_vdef (s2)))
+	    return false;
+	  if (TREE_CODE (lhs1) != SSA_NAME
+	      && TREE_CODE (lhs2) != SSA_NAME)
+	    return true;
+	}
       return (TREE_CODE (lhs1) == SSA_NAME
 	      && TREE_CODE (lhs2) == SSA_NAME
 	      && vn_valueize (lhs1) == vn_valueize (lhs2));
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c (revision 189007)
+++ gcc/tree-ssa-sccvn.c (working copy)
@@ -628,6 +628,9 @@ copy_reference_ops_from_ref (tree ref, V
 
       switch (temp.opcode)
 	{
+	case MODIFY_EXPR:
+	  temp.op0 = TREE_OPERAND (ref, 1);
+	  break;
 	case WITH_SIZE_EXPR:
 	  temp.op0 = TREE_OPERAND (ref, 1);
 	  temp.off = 0;
@@ -748,6 +751,7 @@ copy_reference_ops_from_ref (tree ref, V
       VEC_safe_push (vn_reference_op_s, heap, *result, &temp);
 
       if (REFERENCE_CLASS_P (ref)
+	  || TREE_CODE (ref) == MODIFY_EXPR
 	  || TREE_CODE (ref) == WITH_SIZE_EXPR
 	  || (TREE_CODE (ref) == ADDR_EXPR
 	      && !is_gimple_min_invariant (ref)))
@@ -1941,7 +1945,7 @@ vn_reference_lookup (tree op, tree vuse,
    RESULT, and return the resulting reference structure we created.  */
 
 vn_reference_t
-vn_reference_insert (tree op, tree result, tree vuse)
+vn_reference_insert (tree op, tree result, tree vuse, tree vdef)
 {
   void **slot;
   vn_reference_t vr1;
@@ -1957,6 +1961,7 @@ vn_reference_insert (tree op, tree resul
   vr1->set = get_alias_set (op);
   vr1->hashcode = vn_reference_compute_hash (vr1);
   vr1->result = TREE_CODE (result) == SSA_NAME ? SSA_VAL (result) : result;
+  vr1->result_vdef = vdef;
 
   slot = htab_find_slot_with_hash (current_info->references, vr1, vr1->hashcode,
 				   INSERT);
@@ -2775,7 +2780,7 @@ visit_reference_op_load (tree lhs, tree
   else
     {
       changed = set_ssa_val_to (lhs, lhs);
-      vn_reference_insert (op, lhs, last_vuse);
+      vn_reference_insert (op, lhs, last_vuse, NULL_TREE);
     }
 
   return changed;
@@ -2789,8 +2794,11 @@ static bool
 visit_reference_op_store (tree lhs, tree op, gimple stmt)
 {
   bool changed = false;
-  tree result;
+  vn_reference_t vnresult = NULL;
+  tree result, assign;
   bool resultsame = false;
+  tree vuse = gimple_vuse (stmt);
+  tree vdef = gimple_vdef (stmt);
 
   /* First we want to lookup using the *vuses* from the store and see
      if there the last store to this location with the same address
@@ -2808,7 +2816,7 @@ visit_reference_op_store (tree lhs, tree
      Otherwise, the vdefs for the store are used when inserting into
      the table, since the store generates a new memory state.  */
 
-  result = vn_reference_lookup (lhs, gimple_vuse (stmt), VN_NOWALK, NULL);
+  result = vn_reference_lookup (lhs, vuse, VN_NOWALK, NULL);
 
   if (result)
     {
@@ -2821,8 +2829,17 @@ visit_reference_op_store (tree lhs, tree
 
   if (!result || !resultsame)
     {
-      tree vdef;
+      assign = build2 (MODIFY_EXPR, TREE_TYPE (lhs), lhs, op);
+      vn_reference_lookup (assign, vuse, VN_NOWALK, &vnresult);
+      if (vnresult)
+	{
+	  VN_INFO (vdef)->use_processed = true;
+	  return set_ssa_val_to (vdef, vnresult->result_vdef);
+	}
+    }
 
+  if (!result || !resultsame)
+    {
       if (dump_file && (dump_flags & TDF_DETAILS))
 	{
 	  fprintf (dump_file, "No store match\n");
@@ -2834,7 +2851,7 @@ visit_reference_op_store (tree lhs, tree
 	}
       /* Have to set value numbers before insert, since insert is
 	 going to valueize the references in-place.  */
-      if ((vdef = gimple_vdef (stmt)))
+      if (vdef)
 	{
 	  changed |= set_ssa_val_to (vdef, vdef);
 	}
@@ -2842,22 +2859,21 @@ visit_reference_op_store (tree lhs, tree
       /* Do not insert structure copies into the tables.  */
       if (is_gimple_min_invariant (op)
 	  || is_gimple_reg (op))
-        vn_reference_insert (lhs, op, vdef);
+        vn_reference_insert (lhs, op, vdef, NULL);
+
+      assign = build2 (MODIFY_EXPR, TREE_TYPE (lhs), lhs, op);
+      vn_reference_insert (assign, lhs, vuse, vdef);
     }
   else
     {
       /* We had a match, so value number the vdef to have the value
 	 number of the vuse it came from.  */
-      tree def, use;
 
       if (dump_file && (dump_flags & TDF_DETAILS))
 	fprintf (dump_file, "Store matched earlier value,"
 		 "value numbering store vdefs to matching vuses.\n");
 
-      def = gimple_vdef (stmt);
-      use = gimple_vuse (stmt);
-
-      changed |= set_ssa_val_to (def, SSA_VAL (use));
+      changed |= set_ssa_val_to (vdef, SSA_VAL (vuse));
     }
 
   return changed;
Index: gcc/tree-ssa-sccvn.h
===================================================================
--- gcc/tree-ssa-sccvn.h (revision 189007)
+++ gcc/tree-ssa-sccvn.h (working copy)
@@ -200,7 +200,7 @@ tree vn_reference_lookup_pieces (tree, a
 				 VEC (vn_reference_op_s, heap) *,
 				 vn_reference_t *, vn_lookup_kind);
 tree vn_reference_lookup (tree, tree, vn_lookup_kind, vn_reference_t *);
-vn_reference_t vn_reference_insert (tree, tree, tree);
+vn_reference_t vn_reference_insert (tree, tree, tree, tree);
 vn_reference_t vn_reference_insert_pieces (tree, alias_set_type, tree,
 					   VEC (vn_reference_op_s, heap) *,
 					   tree, unsigned int);
Index: gcc/testsuite/gcc.dg/pr51879-7.c
===================================================================
--- /dev/null (new file)
+++ gcc/testsuite/gcc.dg/pr51879-7.c (revision 0)
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-pre" } */
+
+int bar (int);
+
+int z;
+
+void
+foo (int y)
+{
+  if (y == 6)
+    z = 5;
+  else
+    z = 5;
+}
+
+/* { dg-final { scan-tree-dump-times "z = 5" 1 "pre"} } */
+/* { dg-final { cleanup-tree-dump "pre" } } */
Index: gcc/testsuite/gcc.dg/pr51879-18.c
===================================================================
--- /dev/null (new file)
+++ gcc/testsuite/gcc.dg/pr51879-18.c (revision 0)
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-pre -fno-tree-copy-prop -fno-tree-dominator-opts -fno-tree-copyrename" } */
+
+extern int foo (void);
+
+void bar (int c, int *p)
+{
+  int *q = p;
+
+  if (c)
+    *p = foo ();
+  else
+    *q = foo ();
+}
+
+/* { dg-final { scan-tree-dump-times "foo \\(" 1 "pre"} } */
+/* { dg-final { cleanup-tree-dump "pre" } } */