(check_dbra_loop): When reversing loop when

no_use_except_counting is false, there must be only one biv.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@9642 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/loop.c b/gcc/loop.c
index 5507e09..f6fc598 100644 (file)
--- a/gcc/loop.c
+++ b/gcc/loop.c
@@ -5724,6 +5724,11 @@ check_dbra_loop (loop_end, insn_count, loop_start)
         all memory references have non-overlapping addresses
         (obviously true if only one write)
         allow 2 insns for the compare/jump at the end of the loop.  */
+      /* Also, we must avoid any instructions which use both the reversed
+        biv and another biv.  Such instructions will fail if the loop is
+        reversed.  We meet this condition by requiring that either
+        no_use_except_counting is true, or else that there is only
+        one biv.  */
       int num_nonfixed_reads = 0;
       /* 1 if the iteration var is used only to count iterations.  */
       int no_use_except_counting = 0;
@@ -5788,8 +5793,9 @@ check_dbra_loop (loop_end, insn_count, loop_start)
          && !loop_has_volatile
          && reversible_mem_store
          && (no_use_except_counting
-             || (bl->giv_count + bl->biv_count + num_mem_sets
-                 + num_movables + 2 == insn_count)))
+             || ((bl->giv_count + bl->biv_count + num_mem_sets
+                  + num_movables + 2 == insn_count)
+                 && (bl == loop_iv_list && bl->next == 0))))
        {
          rtx tem;