2009-07-01 Richard Guenther <rguenther@suse.de>

[pf3gnuchains/gcc-fork.git] / gcc / tree-ssa-dce.c

diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index 0cb8ac6..6be298e 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 +671,26 @@ 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))
            {
+             tree callee = gimple_call_fndecl (stmt);
              unsigned i;
 
+             /* Calls to functions that are merely acting as barriers
+                or that only store to memory do not make any previous
+                stores necessary.  */
+             if (callee != NULL_TREE
+                 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
+                 && (DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET
+                     || DECL_FUNCTION_CODE (callee) == BUILT_IN_MALLOC
+                     || DECL_FUNCTION_CODE (callee) == BUILT_IN_FREE))
+               continue;
+
              /* 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 +704,7 @@ 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 +716,7 @@ 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)