* alias.c (true_dependence): Allow non-unchanging read to conflict

	with unchanging write.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@36476 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 8c48b71..cf76042 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -13,6 +13,9 @@ Sun Sep 17 18:48:32 2000  Denis Chertykov  <denisc@overta.ru>
 
 Sun Sep 17 10:46:17 2000  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>
 
+       * alias.c (true_dependence): Allow non-unchanging read to conflict
+       with unchanging write.
+
        * expr.c (store_constructor_field): Accept ALIAS_SET arg.
        (store_constructor): Pass alias_set to it.
 

diff --git a/gcc/alias.c b/gcc/alias.c
index be46281..65b053f 100644 (file)
--- a/gcc/alias.c
+++ b/gcc/alias.c
@@ -1600,10 +1600,13 @@ true_dependence (mem, mem_mode, x, varies)
      A non-unchanging read can conflict with a non-unchanging write.
      An unchanging read can conflict with an unchanging write since
      there may be a single store to this address to initialize it.
+     Note that an unchanging store can conflict with a non-unchanging read
+     since we have to make conservative assumptions when we have a
+     record with readonly fields and we are copying the whole thing.
      Just fall through to the code below to resolve potential conflicts.
      This won't handle all cases optimally, but the possible performance
      loss should be negligible.  */
-  if (RTX_UNCHANGING_P (x) != RTX_UNCHANGING_P (mem))
+  if (RTX_UNCHANGING_P (x) && ! RTX_UNCHANGING_P (mem))
     return 0;
 
   if (mem_mode == VOIDmode)