Fix PR47271: only if-convert full writes.

2011-01-25  Sebastian Pop  <sebastian.pop@amd.com>
	    Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/47271
	* tree-if-conv.c (bb_postdominates_preds): New.
	(if_convertible_bb_p): Call bb_postdominates_preds.
	(if_convertible_loop_p_1): Compute CDI_POST_DOMINATORS.
	(predicate_scalar_phi): Call bb_postdominates_preds.

	* gcc.dg/tree-ssa/ifc-pr47271.c: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@169233 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 23 insertions, 0 deletions

diff --git a/gcc/tree-if-conv.c b/gcc/tree-if-conv.c
index 46b20c26c19..ca8f84a54cf 100644
--- a/gcc/tree-if-conv.c
+++ b/gcc/tree-if-conv.c
@@ -716,6 +716,20 @@ if_convertible_stmt_p (gimple stmt, VEC (data_reference_p, heap) *refs)
   return true;
 }
 
+/* Return true when BB post-dominates all its predecessors.  */
+
+static bool
+bb_postdominates_preds (basic_block bb)
+{
+  unsigned i;
+
+  for (i = 0; i < EDGE_COUNT (bb->preds); i++)
+    if (!dominated_by_p (CDI_POST_DOMINATORS, EDGE_PRED (bb, i)->src, bb))
+      return false;
+
+  return true;
+}
+
 /* Return true when BB is if-convertible.  This routine does not check
    basic block's statements and phis.
 
@@ -774,6 +788,11 @@ if_convertible_bb_p (struct loop *loop, basic_block bb, basic_block exit_bb)
 	return false;
       }
 
+  if (EDGE_COUNT (bb->preds) == 2
+      && bb != loop->header
+      && !bb_postdominates_preds (bb))
+    return false;
+
   return true;
 }
 
@@ -992,6 +1011,7 @@ if_convertible_loop_p_1 (struct loop *loop,
     return false;
 
   calculate_dominance_info (CDI_DOMINATORS);
+  calculate_dominance_info (CDI_POST_DOMINATORS);
 
   /* Allow statements that can be handled during if-conversion.  */
   ifc_bbs = get_loop_body_in_if_conv_order (loop);
@@ -1262,6 +1282,9 @@ predicate_scalar_phi (gimple phi, tree cond,
 	  arg_1 = gimple_phi_arg_def (phi, 1);
 	}
 
+      gcc_checking_assert (bb == bb->loop_father->header
+			   || bb_postdominates_preds (bb));
+
       /* Build new RHS using selected condition and arguments.  */
       rhs = build3 (COND_EXPR, TREE_TYPE (res),
 		    unshare_expr (cond), arg_0, arg_1);