* loop.c (check_dbra_loop): The loop ending comparison value

        must be an invariant or we can not reverse the loop.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@22045 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 9 insertions, 0 deletions

diff --git a/gcc/loop.c b/gcc/loop.c
index 3301f7d2f29..cd257be9c35 100644
--- a/gcc/loop.c
+++ b/gcc/loop.c
@@ -6904,6 +6904,15 @@ check_dbra_loop (loop_end, insn_count, loop_start)
 	      comparison_sign_mask
 		= (unsigned HOST_WIDE_INT)1 << (comparison_const_width - 1);
 
+	      /* If the comparison value is not a loop invariant, then we
+		 can not reverse this loop.
+
+		 ??? If the insns which initialize the comparison value as
+		 a whole compute an invariant result, then we could move
+		 them out of the loop and proceed with loop reversal.  */
+	      if (!invariant_p (comparison_val))
+		return 0;
+
 	      if (GET_CODE (comparison_value) == CONST_INT)
 		comparison_val = INTVAL (comparison_value);
 	      initial_value = bl->initial_value;