Fix create_expression_by_pieces (PR tree-optimization/56381)

--- gcc/tree-ssa-pre.c.jj	2013-01-15 09:04:49.000000000 +0100
+++ gcc/tree-ssa-pre.c	2013-02-18 20:24:59.334937995 +0100
@@ -2923,7 +2923,7 @@  create_expression_by_pieces (basic_block
 		break;
 	      case 3:
 		folded = fold_build3 (nary->opcode, nary->type,
-				      genop[0], genop[1], genop[3]);
+				      genop[0], genop[1], genop[2]);
 		break;
 	      default:
 		gcc_unreachable ();
--- gcc/testsuite/g++.dg/opt/pr56381.C.jj	2013-02-18 20:32:56.819214672 +0100
+++ gcc/testsuite/g++.dg/opt/pr56381.C	2013-02-18 20:32:34.000000000 +0100
@@ -0,0 +1,156 @@ 
+// PR tree-optimization/56381
+// { dg-do compile }
+// { dg-options "-std=c++11 -O2 -w" }
+
+template <class>
+class intrusive_ptr {};
+class BasicReferenceCounted
+{
+};
+template <class T>
+class ReferenceCountingPointer : intrusive_ptr <T>
+{
+};
+typedef BasicReferenceCounted ReferenceCountedInConditions;
+class PointTag;
+template <typename T, typename>
+struct PreciseFloatType
+{
+  typedef T Type;
+};
+template <typename T, int N>
+struct ExtVecTraits
+{
+  typedef T __attribute__ ((vector_size (N * sizeof (T)))) type;
+};
+template <typename T, int N>
+using ExtVec = typename ExtVecTraits <T, N>::type;
+template <typename T> using Vec4 = ExtVec <T, 4>;
+template <typename Vec>
+Vec cross3 (Vec x, Vec y)
+{
+  Vec x1200 = (Vec) { x[2], x[0] };
+  Vec y2010 { y[2], y[0], y[1], y[0] };
+  Vec x2010 = (Vec) { x[2], x[0], x[1], x[0] };
+  Vec y1200 = (Vec) { y[1], y[0] };
+  return x1200 * y2010 - x2010 * y1200;
+}
+template <typename T>
+struct Rot3
+{
+  typedef Vec4 <T> Vec;
+  Vec axis[3];
+};
+class Basic2DVector
+{
+};
+template <typename T>
+struct Basic3DVector
+{
+  typedef Vec4 <T> MathVector;
+  Basic3DVector (MathVector iv) : v { (iv[0]), (iv[1]), (iv[2]), (iv[3]) } {}
+  T mag2 () {}
+  Basic3DVector unit ()
+  {
+    T my_mag = mag2 ();
+    return (my_mag) ? (*this) * (T () / (my_mag)) : *this;
+  }
+  Basic3DVector
+  cross (Basic3DVector lh) { return cross3 (v, lh.v); }
+  Vec4 <T> v;
+};
+template <class T>
+Basic3DVector <T> operator * (Basic3DVector <T>, T);
+template <class T, class, class>
+struct PV3DBase
+{
+  typedef Basic3DVector <T> BasicVectorType;
+  template <class U>
+  PV3DBase (Basic3DVector <U> v) : theVector (v) {}
+  BasicVectorType basicVector () { return theVector; }
+  T x ();
+  T y ();
+  BasicVectorType theVector;
+};
+class VectorTag;
+template <class T, class FrameTag>
+struct Vector3DBase:public PV3DBase <T, VectorTag, FrameTag>
+{
+  typedef PV3DBase <T, VectorTag, FrameTag> BaseClass;
+  template <class U>
+  Vector3DBase (Basic3DVector <U> v) : BaseClass (v) {}
+  Vector3DBase unit () { return (this->basicVector ().unit ()); }
+  template <class U>
+  Vector3DBase <typename PreciseFloatType <T, U>::Type, FrameTag> cross (Vector3DBase <U, FrameTag> v)
+  {
+    return (this->theVector.cross (v.basicVector ()));
+  }
+};
+template <class T, class FrameTag>
+class Point3DBase : public PV3DBase <T, PointTag, FrameTag>
+{
+};
+template <typename T, typename U, class Frame>
+Vector3DBase <typename PreciseFloatType <T, U>::Type, Frame> operator - (Point3DBase <T, Frame>, Point3DBase <U, Frame>);
+class GlobalTag;
+template <class T>
+struct TkRotation
+{
+  typedef Vector3DBase <T, GlobalTag> GlobalVector;
+  TkRotation (GlobalVector aX, GlobalVector aY)
+  {
+    GlobalVector uX = aX.unit ();
+    GlobalVector uY = aY.unit ();
+    GlobalVector uZ (uX.cross (uY));
+    rot.axis[2] = uZ.basicVector ().v;
+  }
+  Basic3DVector <T> z ();
+  Rot3 <T> rot;
+};
+template <class T>
+struct GloballyPositioned
+{
+  typedef Point3DBase <T, GlobalTag> PositionType;
+  typedef TkRotation <T> RotationType;
+  typedef Point3DBase <T, GlobalTag> GlobalPoint;
+  typedef Vector3DBase <T, GlobalTag> GlobalVector;
+  T iniPhi () { return 999.9978; }
+  GloballyPositioned (PositionType pos, RotationType rot) : thePos (pos), theRot (rot) { resetCache (); }
+  PositionType position () const;
+  RotationType rotation () const;
+  PositionType thePos;
+  RotationType theRot;
+  void resetCache ()
+  {
+    if ((thePos.x () == 0.) && (thePos.y () == 0.))
+      thePhi = 0.;
+    else
+      thePhi = iniPhi ();
+  }
+  T thePhi;
+};
+class Plane;
+using TangentPlane = Plane;
+struct Surface : public GloballyPositioned <float>, ReferenceCountedInConditions
+{
+  typedef GloballyPositioned <float> Base;
+  Surface (PositionType pos, RotationType rot):
+  Base (pos, rot) {}
+};
+struct Plane : Surface
+{
+  template <typename ... Args>
+  Plane (Args ... args):
+  Surface ((args) ...) {}
+};
+class Cylinder : Surface
+{
+  void tangentPlane (const GlobalPoint &) const;
+};
+void
+Cylinder::tangentPlane (const GlobalPoint & aPoint) const
+{
+  GlobalVector yPlane (rotation ().z ());
+  GlobalVector xPlane (yPlane.cross (aPoint - position ()));
+  new TangentPlane (aPoint, RotationType (xPlane, yPlane));
+}