re PR tree-optimization/19786 (Aliasing optimisation bug)

gcc/ChangeLog:
PR tree-optimization/19786
* tree-ssa-alias.c (compute_flow_insensitive_aliasing): Add one
tag to another's may-alias bitmap when adding to the other's list.
gcc/testsuite/ChangeLog:
PR tree-optimization/19786
* g++.dg/tree-ssa/pr19786.C: New.

From-SVN: r95377

gcc/ChangeLog

+2005-02-21  Alexandre Oliva  <aoliva@redhat.com>
+
+	PR tree-optimization/19786
+	* tree-ssa-alias.c (compute_flow_insensitive_aliasing): Add one
+	tag to another's may-alias bitmap when adding to the other's list.
+
 2005-02-21  DJ Delorie  <dj@redhat.com>
 
 	* tree-ssa-loop-ivopts.c (computation_cost): Start register

gcc/testsuite/ChangeLog

+2005-02-21  Alexandre Oliva  <aoliva@redhat.com>
+
+	PR tree-optimization/19786
+	* g++.dg/tree-ssa/pr19786.C: New.
+
 2005-02-21  Tobias Schl"uter  <tobias.schlueter@physik.uni-muenchen.de>
 
 	* lib/gfortran-dg.exp (gfortran-dg-test): Split long regexps.

gcc/testsuite/g++.dg/tree-ssa/pr19786.C

+// { dg-do run }
+/* { dg-options "-O2" } */
+
+// We used to get alias grouping wrong on this one, hoisting accesses
+// to the vector's end out of the loop.
+
+#include <vector>
+#include <cassert>
+
+struct A
+{
+  double unused;      // If I remove it => it works.
+  std::vector<int> v;
+
+  A() : v(1) {}
+};
+
+inline // If not inline => it works.
+A g()
+{
+  A r;
+  r.v.resize(2);
+  r.v[0] = 1;
+
+  while (!r.v.empty() && r.v.back() == 0)
+    r.v.pop_back();
+
+  return r;
+}
+
+A f(const A &a)
+{
+  if (a.v.empty())  return a;
+  if (a.v.empty())  return a;
+
+  // A z = g(); return z;  // If I return like this => it works.
+  return g();
+}
+
+int main()
+{
+  A a;
+  A b;
+  A r = f(a);
+  assert(r.v.size() != 0);
+
+  return 0;
+}

gcc/tree-ssa-alias.c

@@ -1116,6 +1116,7 @@ compute_flow_insensitive_aliasing (struct alias_info *ai)
 	      /* Since TAG2 does not have any aliases of its own, add
 		 TAG2 itself to the alias set of TAG1.  */
 	      add_may_alias (tag1, tag2);
+	      SET_BIT (may_aliases1, var_ann (tag2)->uid);
 	    }
 	}
     }