Add support for pointers to the language.

Pointers can be either uniform or varying, and behave correspondingly.
e.g.: "uniform float * varying" is a varying pointer to uniform float
data in memory, and "float * uniform" is a uniform pointer to varying
data in memory.  Like other types, pointers are varying by default.

Pointer-based expressions, & and *, sizeof, ->, pointer arithmetic,
and the array/pointer duality all bahave as in C.  Array arguments
to functions are converted to pointers, also like C.

There is a built-in NULL for a null pointer value; conversion from
compile-time constant 0 values to NULL still needs to be implemented.

Other changes:
- Syntax for references has been updated to be C++ style; a useful
  warning is now issued if the "reference" keyword is used.
- It is now illegal to pass a varying lvalue as a reference parameter
  to a function; references are essentially uniform pointers.
  This case had previously been handled via special case call by value
  return code.  That path has been removed, now that varying pointers
  are available to handle this use case (and much more).
- Some stdlib routines have been updated to take pointers as
  arguments where appropriate (e.g. prefetch and the atomics).
  A number of others still need attention.
- All of the examples have been updated
- Many new tests

TODO: documentation

examples/aobench/ao.ispc

@@ -75,7 +75,7 @@ static inline vec vcross(vec v0, vec v1) {
     return ret;
 }
 
-static inline void vnormalize(reference vec v) {
+static inline void vnormalize(vec &v) {
     float len2 = dot(v, v);
     float invlen = rsqrt(len2);
     v *= invlen;
@@ -83,8 +83,7 @@ static inline void vnormalize(reference vec v) {
 
 
 static inline void
-ray_plane_intersect(reference Isect isect, reference Ray ray, 
-                    reference Plane plane) {
+ray_plane_intersect(Isect &isect, Ray &ray, Plane &plane) {
     float d = -dot(plane.p, plane.n);
     float v = dot(ray.dir, plane.n);
 
@@ -104,8 +103,7 @@ ray_plane_intersect(reference Isect isect, reference Ray ray,
 
 
 static inline void
-ray_sphere_intersect(reference Isect isect, reference Ray ray, 
-                     reference Sphere sphere) {
+ray_sphere_intersect(Isect &isect, Ray &ray, Sphere &sphere) {
     vec rs = ray.org - sphere.center;
 
     float B = dot(rs, ray.dir);
@@ -127,7 +125,7 @@ ray_sphere_intersect(reference Isect isect, reference Ray ray,
 
 
 static inline void
-orthoBasis(reference vec basis[3], vec n) {
+orthoBasis(vec basis[3], vec n) {
     basis[2] = n;
     basis[1].x = 0.0; basis[1].y = 0.0; basis[1].z = 0.0;
 
@@ -150,8 +148,8 @@ orthoBasis(reference vec basis[3], vec n) {
 
 
 static inline float
-ambient_occlusion(reference Isect isect, reference Plane plane, 
-                  reference Sphere spheres[3], reference RNGState rngstate) {
+ambient_occlusion(Isect &isect, Plane &plane, Sphere spheres[3], 
+                  RNGState &rngstate) {
     float eps = 0.0001f;
     vec p, n;
     vec basis[3];
@@ -168,8 +166,8 @@ ambient_occlusion(reference Isect isect, reference Plane plane,
             Ray ray;
             Isect occIsect;
 
-            float theta = sqrt(frandom(rngstate));
-            float phi   = 2.0f * M_PI * frandom(rngstate);
+            float theta = sqrt(frandom(&rngstate));
+            float phi   = 2.0f * M_PI * frandom(&rngstate);
             float x = cos(phi) * theta;
             float y = sin(phi) * theta;
             float z = sqrt(1.0 - theta * theta);
@@ -205,7 +203,7 @@ ambient_occlusion(reference Isect isect, reference Plane plane,
  */
 static void ao_scanlines(uniform int y0, uniform int y1, uniform int w, 
                          uniform int h,  uniform int nsubsamples, 
-                         reference uniform float image[]) {
+                         uniform float image[]) {
     static Plane plane = { { 0.0f, -0.5f, 0.0f }, { 0.f, 1.f, 0.f } };
     static Sphere spheres[3] = {
         { { -2.0f, 0.0f, -3.5f }, 0.5f },
@@ -213,7 +211,7 @@ static void ao_scanlines(uniform int y0, uniform int y1, uniform int w,
         { { 1.0f, 0.0f, -2.2f }, 0.5f } };
     RNGState rngstate;
 
-    seed_rng(rngstate, y0);
+    seed_rng(&rngstate, y0);
 
     // Compute the mapping between the 'programCount'-wide program
     // instances running in parallel and samples in the image.