Revert "Revert "Fix ShapeTracker mismatch in LazyBuffer.fromCPU (#1156)" (#1181)" + add test

This reverts commit a374b62bfe.

test/test_lazybuffer.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python
+import numpy as np
+import unittest
+from tinygrad.lazy import LazyBuffer
+
+class TestLazyBuffer(unittest.TestCase):
+  def test_fromcpu_buffer_sharing(self):
+    a = np.arange(8)
+    assert LazyBuffer.fromCPU(a).realized._buf is a
+
+  def test_fromcpu_shape_tracker(self):
+    def helper(a: np.ndarray):
+      print(a.shape, a.strides, a.flags.c_contiguous)
+      b = LazyBuffer.fromCPU(a).realize()
+      assert b.st.contiguous == a.flags.c_contiguous
+      assert b.st.shape == a.shape
+      np.testing.assert_equal(a, b.toCPU())
+
+    for ndims in range(1, 4):
+      a = np.random.randn(*(4,)*ndims).astype(np.float32)
+      for stride in [-2, 1, 2]:
+        for start in [0, 1]:
+          helper(a[(slice(start, None, stride),)*ndims])
+
+if __name__ == "__main__":
+  unittest.main()

tinygrad/lazy.py

@@ -8,7 +8,7 @@ import numpy as np
 from tinygrad.helpers import GRAPH, DEBUG, prod, getenv, DType, dtypes, flatten, ImageDType, LightWeakSet, LightWeakValueDictionary
 from tinygrad.runtime.ops_cpu import RawNumpyBuffer
 from tinygrad.runtime.ops_disk import RawDiskBuffer
-from tinygrad.shape.shapetracker import MovementOps, ShapeTracker, get_contraction
+from tinygrad.shape.shapetracker import MovementOps, ShapeTracker, View, get_contraction
 from tinygrad.ops import Compiled, Interpreted, UnaryOps, BinaryOps, ReduceOps, LoadOps, OpType, LazyOp
 from tinygrad.runtime.lib import RawBufferMapped, RawConst, RawBuffer
 
@@ -176,7 +176,7 @@ class LazyBuffer:
 
   @staticmethod
   def fromCPU(x: np.ndarray) -> LazyBuffer:
-    return LazyBuffer("CPU", ShapeTracker(x.shape), LoadOps, LazyOp(LoadOps.EMPTY, (), None), dtypes.from_np(x.dtype), RawNumpyBuffer.fromCPU(x))
+    return LazyBuffer("CPU", ShapeTracker(x.shape, [View(x.shape, tuple(st//x.itemsize for st in x.strides))]), LoadOps, LazyOp(LoadOps.EMPTY, (), None), dtypes.from_np(x.dtype), RawNumpyBuffer.fromCPU(x))
 
   # create a constant with the shape and dtype of self
   def const_like(self, val) -> LazyBuffer: