[PATCH, COMMITTED, PR 41282] Allow build_ref_for_offset to fail when propagating SRA accesses accross assignments

[Martin Jambor <mjambor at suse dot cz>]

Hi,

when unions are assigned to structures like in the testcase below, SRA
might try to ask build_ref_for_offset to carry out an impossible task
and ICEd on an assert if it failed.  The patch below changes SRA to
handle such cases gracefully.

Bootstrapped and regression tested on x86_64-linux.  Approved by Richi
in bugzilla.

Thanks,

Martin


2009-09-07  Martin Jambor  <mjambor@suse.cz>

	PR middle-end/41282
	* tree-sra.c (create_artificial_child_access): Return NULL if
	build_ref_for_offset fails.
	(propagate_subacesses_accross_link): Allow build_ref_for_offset
	and create_artificial_child_access to fail.

	* testsuite/gcc.c-torture/compile/pr41282.c: New test.


Index: mine/gcc/tree-sra.c
===================================================================
--- mine.orig/gcc/tree-sra.c
+++ mine/gcc/tree-sra.c
@@ -1518,9 +1518,9 @@ child_would_conflict_in_lacc (struct acc
 
 /* Create a new child access of PARENT, with all properties just like MODEL
    except for its offset and with its grp_write false and grp_read true.
-   Return the new access. Note that this access is created long after all
-   splicing and sorting, it's not located in any access vector and is
-   automatically a representative of its group.  */
+   Return the new access or NULL if it cannot be created.  Note that this access
+   is created long after all splicing and sorting, it's not located in any
+   access vector and is automatically a representative of its group.  */
 
 static struct access *
 create_artificial_child_access (struct access *parent, struct access *model,
@@ -1528,22 +1528,23 @@ create_artificial_child_access (struct a
 {
   struct access *access;
   struct access **child;
-  bool ok;
+  tree expr = parent->base;;
 
   gcc_assert (!model->grp_unscalarizable_region);
 
+  if (!build_ref_for_offset (&expr, TREE_TYPE (expr), new_offset,
+			     model->type, false))
+    return NULL;
+
   access = (struct access *) pool_alloc (access_pool);
   memset (access, 0, sizeof (struct access));
   access->base = parent->base;
+  access->expr = expr;
   access->offset = new_offset;
   access->size = model->size;
   access->type = model->type;
   access->grp_write = true;
   access->grp_read = false;
-  access->expr = access->base;
-  ok = build_ref_for_offset (&access->expr, TREE_TYPE (access->expr),
-			     new_offset, access->type, false);
-  gcc_assert (ok);
 
   child = &parent->first_child;
   while (*child && (*child)->offset < new_offset)
@@ -1558,7 +1559,7 @@ create_artificial_child_access (struct a
 
 /* Propagate all subaccesses of RACC across an assignment link to LACC. Return
    true if any new subaccess was created.  Additionally, if RACC is a scalar
-   access but LACC is not, change the type of the latter.  */
+   access but LACC is not, change the type of the latter, if possible.  */
 
 static bool
 propagate_subacesses_accross_link (struct access *lacc, struct access *racc)
@@ -1575,13 +1576,14 @@ propagate_subacesses_accross_link (struc
   if (!lacc->first_child && !racc->first_child
       && is_gimple_reg_type (racc->type))
     {
-      bool ok;
+      tree t = lacc->base;
 
-      lacc->expr = lacc->base;
-      ok = build_ref_for_offset (&lacc->expr, TREE_TYPE (lacc->expr),
-			     lacc->offset, racc->type, false);
-      gcc_assert (ok);
-      lacc->type = racc->type;
+      if (build_ref_for_offset (&t, TREE_TYPE (t), lacc->offset, racc->type,
+				false))
+	{
+	  lacc->expr = t;
+	  lacc->type = racc->type;
+	}
       return false;
     }
 
@@ -1615,10 +1617,12 @@ propagate_subacesses_accross_link (struc
 
       rchild->grp_hint = 1;
       new_acc = create_artificial_child_access (lacc, rchild, norm_offset);
-      if (racc->first_child)
-	propagate_subacesses_accross_link (new_acc, rchild);
-
-      ret = true;
+      if (new_acc)
+	{
+	  ret = true;
+	  if (racc->first_child)
+	    propagate_subacesses_accross_link (new_acc, rchild);
+	}
     }
 
   return ret;
Index: mine/gcc/testsuite/gcc.c-torture/compile/pr41282.c
===================================================================
--- /dev/null
+++ mine/gcc/testsuite/gcc.c-torture/compile/pr41282.c
@@ -0,0 +1,20 @@
+struct S
+{
+  unsigned int iu;
+};
+
+union U
+{
+  struct S s;
+  signed int is;
+};
+
+extern signed int bar ();
+
+struct S foo (void)
+{
+  union U u;
+
+  u.is = bar ();
+  return u.s;
+}