re PR tree-optimization/65217 (__builtin_unreachable in if statement causes bad…

re PR tree-optimization/65217 (__builtin_unreachable in if statement causes bad assembly generation)

	PR tree-optimization/65217
	* tree-ssa-dom.c (record_equality): Given two SSA_NAMEs, if just one
	of them has a single use, make sure it is the LHS of the implied
	copy.

        PR tree-optimization/65217
	* gcc.target/i386/pr65217.c: Remove XFAIL.

From-SVN: r222499

gcc/ChangeLog

+2015-04-27  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/65217
+	* tree-ssa-dom.c (record_equality): Given two SSA_NAMEs, if just one
+	of them has a single use, make sure it is the LHS of the implied
+	copy.
+
 2015-04-28  Alan Modra  <amodra@gmail.com>
 
 	PR target/65810

gcc/testsuite/ChangeLog

+2015-04-27  Jeff Law <law@redhat.com>
+
+        PR tree-optimization/65217
+	* gcc.target/i386/pr65217.c: Remove XFAIL.
+
 2015-04-27  Andre Vehreschild  <vehre@gmx.de>
 
 	PR fortran/60322

gcc/testsuite/gcc.target/i386/pr65217.c

 /* { dg-do compile } */
 /* { dg-options "-O" } */
-/* { dg-final { scan-assembler-not "negl" { xfail *-*-* } } } */
-/* { dg-final { scan-assembler-not "andl" { xfail *-*-* } } } */
+/* { dg-final { scan-assembler-not "negl" } } */
+/* { dg-final { scan-assembler-not "andl" } } */
 
 int 
 test(int n)

gcc/tree-ssa-dom.c

@@ -1762,6 +1762,20 @@ record_equality (tree x, tree y)
   if (tree_swap_operands_p (x, y, false))
     std::swap (x, y);
 
+  /* Most of the time tree_swap_operands_p does what we want.  But there's
+     cases where we we know one operand is better for copy propagation than
+     the other.  Given no other code cares about ordering of equality
+     comparison operators for that purpose, we just handle the special cases
+     here.  */
+  if (TREE_CODE (x) == SSA_NAME && TREE_CODE (y) == SSA_NAME)
+    {
+      /* If one operand is a single use operand, then make it
+	 X.  This will preserve its single use properly and if this
+	 conditional is eliminated, the computation of X can be
+	 eliminated as well.  */
+      if (has_single_use (y) && ! has_single_use (x))
+	std::swap (x, y);
+    }
   if (TREE_CODE (x) == SSA_NAME)
     prev_x = SSA_NAME_VALUE (x);
   if (TREE_CODE (y) == SSA_NAME)