add collapse_view to the scheduler [pr] (#8440)

test/test_schedule.py

@@ -1981,6 +1981,39 @@ class TestView(unittest.TestCase):
     run_schedule(sched)
     np.testing.assert_allclose(b.numpy(), np.pad(a.numpy(), ((0, 5), (0, 0)))[5:])
 
+  # a*VIEW(x), where VIEW(x) = 0
+  # x collapses along with its children
+  def test_parent_view_collapses(self):
+    a = Tensor([1, 2])
+    b = Tensor.arange(3).contiguous()
+    bv = b.pad(((0, 2),))[-2:]
+    # this becomes a late a*0
+    late_mul = a*bv
+    check_schedule(late_mul, 0)
+    # the arange doesn't realize
+    self.assertIsNone(b.lazydata.base.realized)
+    # mul doesn't realize
+    self.assertIsNone(late_mul.lazydata.base.realized)
+    self.assertEqual(late_mul.tolist(), [0, 0])
+
+  # SINK has two branches:
+  # a*VIEW(x), where VIEW(x) = 0
+  # x+2
+  # as long as one child realizes, x does not collapse
+  def test_parent_multiple_children_no_collapse(self):
+    a = Tensor([1, 2])
+    b = Tensor.arange(3).contiguous()
+    bv = b.pad(((0, 2),))[-2:]
+    late_mul = a*bv
+    other_child = b+2
+    s = check_schedule([late_mul, other_child], 2)
+    # the arange realizes
+    self.assertIsNotNone(b.lazydata.base.realized)
+    # mul still collapses
+    self.assertIsNone(late_mul.lazydata.base.realized)
+    run_schedule(s)
+    self.assertEqual(other_child.tolist(), [2, 3, 4])
+
 def tensor_rewrite(t) -> UOp: return graph_rewrite(t.lazydata.base, remove_movement_ops+symbolic)
 class TestBigGraph(unittest.TestCase):
   def test_sink_childless_const(self):

tinygrad/engine/schedule.py

@@ -553,8 +553,13 @@ def append_uop(ctx:ScheduleContext, view:UOp, buf_uop:UOp) -> None:
   buf_uop.buffer.ref(1)
 create_ctx = PatternMatcher([(UPat(Ops.VIEW, name="view", src=(UPat(Ops.BUFFER, name="buf_uop"), UPat())), append_uop)])
 
+# **** movement ops
+
 remove_movement_ops = PatternMatcher([
   (UPat(GroupOp.Movement, name="x"), lambda x: x.base.view(unwrap(x.st))),
+  # some masked views can collapse to 0, VIEW(x) -> CONST(VIEW)
+  (UPat(Ops.VIEW, name="view"),
+   lambda view: view.const_like(0) if (vm:=view.st.views[-1].mask) is not None and any((x[1]-x[0]) == 0 for x in vm) else None),
   # merge one src (unrealized) views
   # NOTE: we can't merge realized buffer views here, because the buffer is realized before the view
   (UPat(Ops.VIEW, src=(UPat(Ops.VIEW, src=(UPat.var("x"),), name="v1")), name="v2"),

tinygrad/ops.py

@@ -487,7 +487,6 @@ class UOp(MathTrait, metaclass=UOpMetaClass):
     if self.st is None: return UOp(Ops.VIEW, self.dtype.base if not isinstance(self.dtype, ImageDType) else self.dtype, (self,), new_st)
     ret = UOp(Ops.VIEW, self.dtype, (self.base,), new_st)
     # instant folding rules
-    if self.st.size == 0 or (new_st.views[-1].mask is not None and any((x[1]-x[0]) == 0 for x in new_st.views[-1].mask)): return ret.const_like(0)
     if new_st.contiguous and self.base.shape == new_st.shape: return self.base
     return ret