* loop.c (first_loop_store_insn): New file-scope variable.

	(prescan_loop): Set it.
	(check_dbra_loop): Check if a store depends on a register
	that is set after the store.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@25034 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6c7fa58..e2edb46 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+Fri Feb  5 07:09:29 1999  J"orn Rennecke <amylaar@cygnus.co.uk>
+
+       * loop.c (first_loop_store_insn): New file-scope variable.
+       (prescan_loop): Set it.
+       (check_dbra_loop): Check if a store depends on a register
+       that is set after the store.
+
 Fri Feb  5 06:55:15 1999  J"orn Rennecke <amylaar@cygnus.co.uk>
 
        * unroll.c (entire file): Remove tabs / spaces at end of lines.

diff --git a/gcc/loop.c b/gcc/loop.c
index f762936..abf90ce 100644 (file)
--- a/gcc/loop.c
+++ b/gcc/loop.c
@@ -173,6 +173,9 @@ static char *moved_once;
 
 static rtx loop_store_mems;
 
+/* The insn where the first of these was found.  */
+static rtx first_loop_store_insn;
+
 typedef struct loop_mem_info {
   rtx mem;      /* The MEM itself.  */
   rtx reg;      /* Corresponding pseudo, if any.  */
@@ -2404,6 +2407,7 @@ prescan_loop (start, end)
   loop_has_volatile = 0;
   loop_has_tablejump = 0;
   loop_store_mems = NULL_RTX;
+  first_loop_store_insn = NULL_RTX;
   loop_mems_idx = 0;
 
   num_mem_sets = 0;
@@ -2456,6 +2460,8 @@ prescan_loop (start, end)
            loop_has_tablejump = 1;
          
          note_stores (PATTERN (insn), note_addr_stored);
+         if (! first_loop_store_insn && loop_store_mems)
+           first_loop_store_insn = insn;
 
          if (! loop_has_multiple_exit_targets
              && GET_CODE (insn) == JUMP_INSN
@@ -7682,9 +7688,26 @@ check_dbra_loop (loop_end, insn_count, loop_start, loop_info)
             case, the insn should have been moved out of the loop.  */
 
          if (num_mem_sets == 1)
-           reversible_mem_store
-             = (! unknown_address_altered
-                && ! invariant_p (XEXP (loop_store_mems, 0)));
+           {
+             struct induction *v;
+
+             reversible_mem_store
+               = (! unknown_address_altered
+                  && ! invariant_p (XEXP (loop_store_mems, 0)));
+
+             /* If the store depends on a register that is set after the
+                store, it depends on the initial value, and is thus not
+                reversible.  */
+             for (v = bl->giv; reversible_mem_store && v; v = v->next_iv)
+               {
+                 if (v->giv_type == DEST_REG
+                     && reg_mentioned_p (v->dest_reg,
+                                         XEXP (loop_store_mems, 0))
+                     && (INSN_LUID (v->insn)
+                         > INSN_LUID (first_loop_store_insn)))
+                   reversible_mem_store = 0;
+               }
+           }
        }
       else
        return 0;