2014-07-14 Richard Biener <rguenther@suse.de>

	PR tree-optimization/61757
	PR tree-optimization/61783
	PR tree-optimization/61787
	* tree-ssa-dom.c (record_equality): Revert canonicalization
	change and add comment.
	(propagate_rhs_into_lhs): Revert previous fix, removing
	loop depth restriction again.

	* gcc.dg/torture/pr61757.c: New testcase.
	* gcc.dg/torture/pr61787.c: Likewise.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@212513 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 32 insertions, 30 deletions

diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c
index 4c0c276a62d..c4ec4e5415c 100644
--- a/gcc/tree-ssa-dom.c
+++ b/gcc/tree-ssa-dom.c
@@ -1589,6 +1589,33 @@ record_const_or_copy (tree x, tree y)
   record_const_or_copy_1 (x, y, prev_x);
 }
 
+/* Return the loop depth of the basic block of the defining statement of X.
+   This number should not be treated as absolutely correct because the loop
+   information may not be completely up-to-date when dom runs.  However, it
+   will be relatively correct, and as more passes are taught to keep loop info
+   up to date, the result will become more and more accurate.  */
+
+static int
+loop_depth_of_name (tree x)
+{
+  gimple defstmt;
+  basic_block defbb;
+
+  /* If it's not an SSA_NAME, we have no clue where the definition is.  */
+  if (TREE_CODE (x) != SSA_NAME)
+    return 0;
+
+  /* Otherwise return the loop depth of the defining statement's bb.
+     Note that there may not actually be a bb for this statement, if the
+     ssa_name is live on entry.  */
+  defstmt = SSA_NAME_DEF_STMT (x);
+  defbb = gimple_bb (defstmt);
+  if (!defbb)
+    return 0;
+
+  return bb_loop_depth (defbb);
+}
+
 /* Similarly, but assume that X and Y are the two operands of an EQ_EXPR.
    This constrains the cases in which we may treat this as assignment.  */
 
@@ -1608,7 +1635,10 @@ record_equality (tree x, tree y)
      long as we canonicalize on one value.  */
   if (is_gimple_min_invariant (y))
     ;
-  else if (is_gimple_min_invariant (x))
+  else if (is_gimple_min_invariant (x)
+	   /* ???  When threading over backedges the following is important
+	      for correctness.  See PR61757.  */
+	   || (loop_depth_of_name (x) <= loop_depth_of_name (y)))
     prev_x = x, x = y, y = prev_x, prev_x = prev_y;
   else if (prev_x && is_gimple_min_invariant (prev_x))
     x = y, y = prev_x, prev_x = prev_y;
@@ -2638,33 +2668,6 @@ get_lhs_or_phi_result (gimple stmt)
     gcc_unreachable ();
 }
 
-/* Return the loop depth of the basic block of the defining statement of X.
-   This number should not be treated as absolutely correct because the loop
-   information may not be completely up-to-date when dom runs.  However, it
-   will be relatively correct, and as more passes are taught to keep loop info
-   up to date, the result will become more and more accurate.  */
-
-static int
-loop_depth_of_name (tree x)
-{
-  gimple defstmt;
-  basic_block defbb;
-
-  /* If it's not an SSA_NAME, we have no clue where the definition is.  */
-  if (TREE_CODE (x) != SSA_NAME)
-    return 0;
-
-  /* Otherwise return the loop depth of the defining statement's bb.
-     Note that there may not actually be a bb for this statement, if the
-     ssa_name is live on entry.  */
-  defstmt = SSA_NAME_DEF_STMT (x);
-  defbb = gimple_bb (defstmt);
-  if (!defbb)
-    return 0;
-
-  return bb_loop_depth (defbb);
-}
-
 /* Propagate RHS into all uses of LHS (when possible).
 
    RHS and LHS are derived from STMT, which is passed in solely so
@@ -2680,8 +2683,7 @@ static void
 propagate_rhs_into_lhs (gimple stmt, tree lhs, tree rhs, bitmap interesting_names)
 {
   /* First verify that propagation is valid.  */
-  if (may_propagate_copy (lhs, rhs)
-      && loop_depth_of_name (lhs) >= loop_depth_of_name (rhs))
+  if (may_propagate_copy (lhs, rhs))
     {
       use_operand_p use_p;
       imm_use_iterator iter;