2009-06-30 Richard Guenther <rguenther@suse.de>

	* tree-ssa-dce.c (mark_all_reaching_defs_necessary_1): Always
	continue walking.
	(propagate_necessity): Do not mark reaching defs of stores
	as necessary.

	* gcc.dg/tree-ssa/ssa-dce-6.c: New testcase.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@149103 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4eb3f62..4cb0958 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2009-06-30  Richard Guenther  <rguenther@suse.de>
+
+       * tree-ssa-dce.c (mark_all_reaching_defs_necessary_1): Always
+       continue walking.
+       (propagate_necessity): Do not mark reaching defs of stores
+       as necessary.
+
 2009-06-30  Jan Hubicka  <jh@suse.cz>
 
        * cfgloopanal.c (check_irred): Move into ...

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 57c377d..a7548d5 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2009-06-30  Richard Guenther  <rguenther@suse.de>
+
+       * gcc.dg/tree-ssa/ssa-dce-6.c: New testcase.
+
 2009-06-30  Wei Guozhi  <carrot@google.com>
 
        * gcc.dg/tree-ssa/ssa-sink-5.c: Change the compiler option "-O2 -Os"

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dce-6.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dce-6.c
new file mode 100644 (file)
index 0000000..30a06a1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dce-6.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-cddce1" } */
+
+struct object { int field; };
+void o(struct object *);
+int globl;
+void t(int x)
+{
+  struct object a, b;
+  struct object *p;
+  o(&a);
+  if (x)
+    p = &a;
+  else
+    p = &b;
+  p->field = 1;
+  globl = 0;
+  return;
+}
+
+/* The global store should not prevent deleting the store to p->field.  */
+
+/* { dg-final { scan-tree-dump-not "p_.->field" "cddce1" } } */
+/* { dg-final { cleanup-tree-dump "cddce1" } } */

diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index 0cb8ac6..8522c5c 100644 (file)
--- a/gcc/tree-ssa-dce.c
+++ b/gcc/tree-ssa-dce.c
@@ -550,9 +550,9 @@ mark_all_reaching_defs_necessary_1 (ao_ref *ref ATTRIBUTE_UNUSED,
        return false;
     }
 
-  /* But can stop after the first necessary statement.  */
   mark_operand_necessary (vdef);
-  return true;
+
+  return false;
 }
 
 static void
@@ -671,18 +671,15 @@ propagate_necessity (struct edge_list *el)
             For 1) we mark all reaching may-defs as necessary, stopping
             at dominating kills.  For 2) we want to mark all dominating
             references necessary, but non-aliased ones which we handle
-            in 1).  Instead of doing so for each load we rely on the
-            worklist to eventually reach all dominating references and
-            instead just mark the immediately dominating references
-            as necessary (but skipping non-aliased ones).  */
+            in 1).  By keeping a global visited bitmap for references
+            we walk for 2) we avoid quadratic behavior for those.  */
 
          if (is_gimple_call (stmt))
            {
              unsigned i;
 
              /* Calls implicitly load from memory, their arguments
-                in addition may explicitly perform memory loads.
-                This also ensures propagation for case 2 for stores.  */
+                in addition may explicitly perform memory loads.  */
              mark_all_reaching_defs_necessary (stmt);
              for (i = 0; i < gimple_call_num_args (stmt); ++i)
                {
@@ -696,7 +693,7 @@ propagate_necessity (struct edge_list *el)
            }
          else if (gimple_assign_single_p (stmt))
            {
-             tree lhs, rhs;
+             tree rhs;
              bool rhs_aliased = false;
              /* If this is a load mark things necessary.  */
              rhs = gimple_assign_rhs1 (stmt);
@@ -708,12 +705,7 @@ propagate_necessity (struct edge_list *el)
                  else
                    rhs_aliased = true;
                }
-             /* If this is an aliased store, mark things necessary.
-                This is where we make sure to propagate for case 2.  */
-             lhs = gimple_assign_lhs (stmt);
-             if (rhs_aliased
-                 || (TREE_CODE (lhs) != SSA_NAME
-                     && ref_may_be_aliased (lhs)))
+             if (rhs_aliased)
                mark_all_reaching_defs_necessary (stmt);
            }
          else if (gimple_code (stmt) == GIMPLE_RETURN)