tree-flow.h (loop_only_exit_p): Declare.

	* tree-flow.h (loop_only_exit_p): Declare.
	* tree-ssa-loop-niter.c (loop_only_exit_p): Make public.
	* tree-ssa-loop-ivopts.c (may_eliminate_iv): Reinstate direct check on
	the number of iterations if it is constant.  Otherwise, if this is the
	only possible exit of the loop, use the conservative estimate on the
	number of iterations of the entire loop if available.

From-SVN: r137437

1 files changed, 27 insertions, 14 deletions

diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 41c3794..ce5c05c 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -3745,13 +3745,12 @@ may_eliminate_iv (struct ivopts_data *data,
   tree nit, period;
   struct loop *loop = data->current_loop;
   aff_tree bnd;
-  double_int period_value, max_niter;
 
   if (TREE_CODE (cand->iv->step) != INTEGER_CST)
     return false;
 
-  /* For now works only for exits that dominate the loop latch.  TODO -- extend
-     for other conditions inside loop body.  */
+  /* For now works only for exits that dominate the loop latch.
+     TODO: extend to other conditions inside loop body.  */
   ex_bb = bb_for_stmt (use->stmt);
   if (use->stmt != last_stmt (ex_bb)
       || TREE_CODE (use->stmt) != COND_EXPR)
@@ -3769,19 +3768,33 @@ may_eliminate_iv (struct ivopts_data *data,
   if (!nit)
     return false;
 
-  /* Determine whether we may use the variable to test whether niter iterations
-     elapsed.  This is the case iff the period of the induction variable is
-     greater than the number of iterations.  */
+  /* Determine whether we can use the variable to test the exit condition.
+     This is the case iff the period of the induction variable is greater
+     than the number of iterations for which the exit condition is true.  */
   period = iv_period (cand->iv);
-  if (!period)
-    return false;
 
-  /* Compare the period with the estimate on the number of iterations of the
-     loop.  */
-  if (!estimated_loop_iterations (loop, true, &max_niter))
-    return false;
-  period_value = tree_to_double_int (period);
-  if (double_int_ucmp (period_value, max_niter) <= 0)
+  /* If the number of iterations is constant, compare against it directly.  */
+  if (TREE_CODE (nit) == INTEGER_CST)
+    {
+      if (!tree_int_cst_lt (nit, period))
+	return false;
+    }
+
+  /* If not, and if this is the only possible exit of the loop, see whether
+     we can get a conservative estimate on the number of iterations of the
+     entire loop and compare against that instead.  */
+  else if (loop_only_exit_p (loop, exit))
+    {
+      double_int period_value, max_niter;
+      if (!estimated_loop_iterations (loop, true, &max_niter))
+	return false;
+      period_value = tree_to_double_int (period);
+      if (double_int_ucmp (max_niter, period_value) >= 0)
+	return false;
+    }
+
+  /* Otherwise, punt.  */
+  else
     return false;
 
   cand_value_at (loop, cand, use->stmt, nit, &bnd);