[Bug tree-optimization/46801] [4.6 Regression] FAIL: gnat.dg/pack9.adb scan-tree-dump-not optimized "gnat_rcheck"

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46801

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.6.0

--- Comment #11 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-30 14:36:37 UTC ---
SRA does

 Pack9.Copy (struct pack9__r2 * const x, struct pack9__r2 * const y)
 {
+  integer t$i2;
   const struct pack9__r2 t;
   integer D.2584;
   integer D.2583;

 <bb 2>:
   t = *y_1(D);
-  D.2583_2 = t.i2;
+  t$i2_9 = y_1(D)->i2;
+  D.2583_2 = t$i2_9;
   D.2584_3 = y_1(D)->i2;
   D.2584_4 = D.2584_3;
   if (D.2583_2 != D.2584_4)
@@ -206,6 +58,7 @@

 <bb 4>:
   *x_5(D) = t;
+  x_5(D)->i2 = t$i2_9;
   return;

 }

thus eliminates 't' and makes D.2583_2 and D.2584_3 redundant (and VN
figure that out and remove the if stmt).

Value-numbering does not see that in

<bb 2>:
  t = *y_1(D);

<bb 3>:
  D.2584_2 = t.i2;
  D.2585_3 = y_1(D)->i2;

the two loads are the same (because it enters (only) the non-rewritten ops
into the hashtable).  See PR52054.