PR tree-opt/42215

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

diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index 8669cdf..cdb6432 100644 (file)
--- a/gcc/tree-ssa-dce.c
+++ b/gcc/tree-ssa-dce.c
@@ -489,6 +489,7 @@ ref_may_be_aliased (tree ref)
 static bitmap visited = NULL;
 static unsigned int longest_chain = 0;
 static unsigned int total_chain = 0;
+static unsigned int nr_walks = 0;
 static bool chain_ovfl = false;
 
 /* Worker for the walker that marks reaching definitions of REF,
@@ -557,6 +558,7 @@ mark_aliased_reaching_defs_necessary (gimple stmt, tree ref)
   if (chain > longest_chain)
     longest_chain = chain;
   total_chain += chain;
+  nr_walks++;
 }
 
 /* Worker for the walker that marks reaching definitions of REF, which
@@ -803,11 +805,16 @@ propagate_necessity (struct edge_list *el)
            gcc_unreachable ();
 
          /* If we over-used our alias oracle budget drop to simple
-            mode.  The cost metric allows quadratic behavior up to
-            a constant maximal chain and after that falls back to
+            mode.  The cost metric allows quadratic behavior
+            (number of uses times number of may-defs queries) up to
+            a constant maximal number of queries and after that falls back to
             super-linear complexity.  */
-         if (longest_chain > 256
-             && total_chain > 256 * longest_chain)
+         if (/* Constant but quadratic for small functions.  */
+             total_chain > 128 * 128
+             /* Linear in the number of may-defs.  */
+             && total_chain > 32 * longest_chain
+             /* Linear in the number of uses.  */
+             && total_chain > nr_walks * 32)
            {
              chain_ovfl = true;
              if (visited)
@@ -1376,7 +1383,9 @@ perform_tree_ssa_dce (bool aggressive)
 
   longest_chain = 0;
   total_chain = 0;
+  nr_walks = 0;
   chain_ovfl = false;
+  visited = BITMAP_ALLOC (NULL);
   propagate_necessity (el);
   BITMAP_FREE (visited);