re PR tree-optimization/81365 (GCC miscompiles swap)

	PR tree-optimization/81365
	* tree-ssa-phiprop.c (propagate_with_phi): When considering hoisting
	aggregate moves onto bb predecessor edges, make sure there are no
	loads that could alias the lhs in between the start of bb and the
	loads from *phi.

	* g++.dg/torture/pr81365.C: New test.

From-SVN: r250261

gcc/ChangeLog

+2017-07-17  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/81365
+	* tree-ssa-phiprop.c (propagate_with_phi): When considering hoisting
+	aggregate moves onto bb predecessor edges, make sure there are no
+	loads that could alias the lhs in between the start of bb and the
+	loads from *phi.
+
 2017-07-17  Georg-Johann Lay  <avr@gjlay.de>
 
 	PR 80929

gcc/testsuite/ChangeLog

 2017-07-17  Jakub Jelinek  <jakub@redhat.com>
 
+	PR tree-optimization/81365
+	* g++.dg/torture/pr81365.C: New test.
+
 	PR tree-optimization/81396
 	* gcc.dg/tree-ssa/pr81396.c: New test.
 

gcc/testsuite/g++.dg/torture/pr81365.C

+// PR tree-optimization/81365
+// { dg-do run }
+
+struct A { unsigned a; };
+
+struct B {
+  B (const A *x)
+  {
+    __builtin_memcpy (b, x, 3 * sizeof (A));
+    __builtin_memcpy (c, x + 3, sizeof (A));
+    __builtin_memset (c + 1, 0, sizeof (A));
+  }
+  bool
+  foo (unsigned x)
+  {
+    A *it = c;
+    if (it->a == x || (++it)->a == x)
+      {
+	A t(b[0]);
+	b[0] = *it;
+	*it = t;
+	return true;
+      }
+    return false;
+  }
+  A b[3];
+  A c[2];
+};
+
+int
+main ()
+{
+  A x[] = { 4, 8, 12, 18 };
+  B y(x);
+  if (!y.foo (18))
+    __builtin_abort ();
+  if (!y.foo (4))
+    __builtin_abort ();
+}

gcc/tree-ssa-phiprop.c

@@ -327,7 +327,7 @@ propagate_with_phi (basic_block bb, gphi *phi, struct phiprop_d *phivn,
       if (!dominated_by_p (CDI_POST_DOMINATORS,
 			   bb, gimple_bb (use_stmt)))
 	continue;
-         
+
       /* Check whether this is a load of *ptr.  */
       if (!(is_gimple_assign (use_stmt)
 	    && gimple_assign_rhs_code (use_stmt) == MEM_REF
@@ -356,6 +356,9 @@ propagate_with_phi (basic_block bb, gphi *phi, struct phiprop_d *phivn,
          insert aggregate copies on the edges instead.  */
       if (!is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
 	{
+	  if (!gimple_vdef (use_stmt))
+	    goto next;
+
 	  /* As we replicate the lhs on each incoming edge all
 	     used SSA names have to be available there.  */
 	  if (! for_each_index (gimple_assign_lhs_ptr (use_stmt),
@@ -363,6 +366,28 @@ propagate_with_phi (basic_block bb, gphi *phi, struct phiprop_d *phivn,
 				get_immediate_dominator (CDI_DOMINATORS,
 							 gimple_bb (phi))))
 	    goto next;
+
+	  gimple *vuse_stmt;
+	  imm_use_iterator vui;
+	  use_operand_p vuse_p;
+	  /* In order to move the aggregate copies earlier, make sure
+	     there are no statements that could read from memory
+	     aliasing the lhs in between the start of bb and use_stmt.
+	     As we require use_stmt to have a VDEF above, loads after
+	     use_stmt will use a different virtual SSA_NAME.  */
+	  FOR_EACH_IMM_USE_FAST (vuse_p, vui, vuse)
+	    {
+	      vuse_stmt = USE_STMT (vuse_p);
+	      if (vuse_stmt == use_stmt)
+		continue;
+	      if (!dominated_by_p (CDI_DOMINATORS,
+				   gimple_bb (vuse_stmt), bb))
+		continue;
+	      if (ref_maybe_used_by_stmt_p (vuse_stmt,
+					    gimple_assign_lhs (use_stmt)))
+		goto next;
+	    }
+
 	  phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
 
 	  /* Remove old stmt.  The phi is taken care of by DCE.  */