re PR rtl-optimization/40924 (miscompiles with -O3 (seemingly related to attribute may_alias))

	PR rtl-optimization/40924
	* dse.c (canon_address): Before calling cselib_expand_value_rtx
	make sure canon_rtx (mem_address) isn't simpler than
	canon_rtx (expanded_mem_address).

	* g++.dg/torture/pr40924.C: New test.

From-SVN: r150483

1 files changed, 67 insertions, 49 deletions

diff --git a/gcc/dse.c b/gcc/dse.c
index 0fc2aa9..2338d32 100644
--- a/gcc/dse.c
+++ b/gcc/dse.c
@@ -1070,6 +1070,8 @@ canon_address (rtx mem,
 {
   rtx mem_address = XEXP (mem, 0);
   rtx expanded_address, address;
+  int expanded;
+
   /* Make sure that cselib is has initialized all of the operands of
      the address before asking it to do the subst.  */
 
@@ -1114,72 +1116,88 @@ canon_address (rtx mem,
       fprintf (dump_file, "\n");
     }
 
-  /* Use cselib to replace all of the reg references with the full
-     expression.  This will take care of the case where we have 
+  /* First see if just canon_rtx (mem_address) is const or frame,
+     if not, try cselib_expand_value_rtx and call canon_rtx on that.  */
+  address = NULL_RTX;
+  for (expanded = 0; expanded < 2; expanded++)
+    {
+      if (expanded)
+	{
+	  /* Use cselib to replace all of the reg references with the full
+	     expression.  This will take care of the case where we have 
 
-     r_x = base + offset;
-     val = *r_x;
+	     r_x = base + offset;
+	     val = *r_x;
    
-     by making it into 
-
-     val = *(base + offset);  
-  */
-
-  expanded_address = cselib_expand_value_rtx (mem_address, scratch, 5);
+	     by making it into 
 
-  /* If this fails, just go with the mem_address.  */
-  if (!expanded_address)
-    expanded_address = mem_address;
+	     val = *(base + offset);  */
 
-  /* Split the address into canonical BASE + OFFSET terms.  */
-  address = canon_rtx (expanded_address);
+	  expanded_address = cselib_expand_value_rtx (mem_address,
+						      scratch, 5);
 
-  *offset = 0;
+	  /* If this fails, just go with the address from first
+	     iteration.  */
+	  if (!expanded_address)
+	    break;
+	}
+      else
+	expanded_address = mem_address;
 
-  if (dump_file)
-    {
-      fprintf (dump_file, "\n   after cselib_expand address: ");
-      print_inline_rtx (dump_file, expanded_address, 0);
-      fprintf (dump_file, "\n");
+      /* Split the address into canonical BASE + OFFSET terms.  */
+      address = canon_rtx (expanded_address);
 
-      fprintf (dump_file, "\n   after canon_rtx address: ");
-      print_inline_rtx (dump_file, address, 0);
-      fprintf (dump_file, "\n");
-    }
+      *offset = 0;
 
-  if (GET_CODE (address) == CONST)
-    address = XEXP (address, 0);
+      if (dump_file)
+	{
+	  if (expanded)
+	    {
+	      fprintf (dump_file, "\n   after cselib_expand address: ");
+	      print_inline_rtx (dump_file, expanded_address, 0);
+	      fprintf (dump_file, "\n");
+	    }
 
-  if (GET_CODE (address) == PLUS && CONST_INT_P (XEXP (address, 1)))
-    {
-      *offset = INTVAL (XEXP (address, 1));
-      address = XEXP (address, 0);
-    }
+	  fprintf (dump_file, "\n   after canon_rtx address: ");
+	  print_inline_rtx (dump_file, address, 0);
+	  fprintf (dump_file, "\n");
+	}
 
-  if (const_or_frame_p (address))
-    {
-      group_info_t group = get_group_info (address);
+      if (GET_CODE (address) == CONST)
+	address = XEXP (address, 0);
 
-      if (dump_file)
-	fprintf (dump_file, "  gid=%d offset=%d \n", group->id, (int)*offset);
-      *base = NULL;
-      *group_id = group->id;
-    }
-  else
-    {
-      *base = cselib_lookup (address, Pmode, true);
-      *group_id = -1;
+      if (GET_CODE (address) == PLUS
+	  && CONST_INT_P (XEXP (address, 1)))
+	{
+	  *offset = INTVAL (XEXP (address, 1));
+	  address = XEXP (address, 0);
+	}
 
-      if (*base == NULL)
+      if (const_or_frame_p (address))
 	{
+	  group_info_t group = get_group_info (address);
+
 	  if (dump_file)
-	    fprintf (dump_file, " no cselib val - should be a wild read.\n");
-	  return false;
+	    fprintf (dump_file, "  gid=%d offset=%d \n",
+		     group->id, (int)*offset);
+	  *base = NULL;
+	  *group_id = group->id;
+	  return true;
 	}
+    }
+
+  *base = cselib_lookup (address, Pmode, true);
+  *group_id = -1;
+
+  if (*base == NULL)
+    {
       if (dump_file)
-	fprintf (dump_file, "  varying cselib base=%d offset = %d\n", 
-		 (*base)->value, (int)*offset);
+	fprintf (dump_file, " no cselib val - should be a wild read.\n");
+      return false;
     }
+  if (dump_file)
+    fprintf (dump_file, "  varying cselib base=%d offset = %d\n", 
+	     (*base)->value, (int)*offset);
   return true;
 }