compiler: Properly implement NumPy array slicing

Strided slicing of one-dimensional arrays (i.e. with non-trivial
steps) might have previously been working, but would have had
different semantics, as all slices were copies rather than a view
into the original data.

Fixing this in the future will require adding support for an index
stride field/tuple to our array representation (and all the
associated indexing logic).

GitHub: Fixes #1627.
This commit is contained in:
David Nadlinger 2021-03-14 19:57:01 +00:00 committed by Sebastien Bourdeauducq
parent 8a892af244
commit 925014689e
5 changed files with 162 additions and 74 deletions

View File

@ -1116,7 +1116,11 @@ class ARTIQIRGenerator(algorithm.Visitor):
_readable_name(index))))
if self.current_assign is None:
return indexed
else: # Slice
else:
# This is a slice. The endpoint checking logic is the same for both lists
# and NumPy arrays, but the actual implementations differ while slices of
# built-in lists are always copies in Python, they are views sharing the
# same backing storage in NumPy.
length = self.iterable_len(value, node.slice.type)
if node.slice.lower is not None:
@ -1141,91 +1145,127 @@ class ARTIQIRGenerator(algorithm.Visitor):
mapped_stop_index = self._map_index(length, stop_index, one_past_the_end=True,
loc=node.begin_loc)
if node.slice.step is not None:
try:
old_assign, self.current_assign = self.current_assign, None
step = self.visit(node.slice.step)
finally:
self.current_assign = old_assign
if builtins.is_array(node.type):
# To implement strided slicing with the proper NumPy reference
# semantics, the pointer/length array representation will need to be
# extended by another field to hold a variable stride.
assert node.slice.step is None, (
"array slices with non-trivial step "
"should have been disallowed during type inference")
# One-dimensionally slicing an array only affects the outermost
# dimension.
shape = self.append(ir.GetAttr(value, "shape"))
lengths = [
self.append(ir.GetAttr(shape, i))
for i in range(len(shape.type.elts))
]
# Compute outermost length zero for "backwards" indices.
raw_len = self.append(
ir.Arith(ast.Sub(loc=None), mapped_stop_index, mapped_start_index))
is_neg_len = self.append(
ir.Compare(ast.Lt(loc=None), raw_len, ir.Constant(0, raw_len.type)))
outer_len = self.append(
ir.Select(is_neg_len, ir.Constant(0, raw_len.type), raw_len))
new_shape = self._make_array_shape([outer_len] + lengths[1:])
# Offset buffer pointer by start index (times stride for inner dims).
stride = reduce(
lambda l, r: self.append(ir.Arith(ast.Mult(loc=None), l, r)),
lengths[1:], ir.Constant(1, lengths[0].type))
offset = self.append(
ir.Arith(ast.Mult(loc=None), stride, mapped_start_index))
buffer = self.append(ir.GetAttr(value, "buffer"))
new_buffer = self.append(ir.Offset(buffer, offset))
return self.append(ir.Alloc([new_buffer, new_shape], node.type))
else:
if node.slice.step is not None:
try:
old_assign, self.current_assign = self.current_assign, None
step = self.visit(node.slice.step)
finally:
self.current_assign = old_assign
self._make_check(
self.append(ir.Compare(ast.NotEq(loc=None), step, ir.Constant(0, step.type))),
lambda: self.alloc_exn(builtins.TException("ValueError"),
ir.Constant("step cannot be zero", builtins.TStr())),
loc=node.slice.step.loc)
else:
step = ir.Constant(1, node.slice.type)
counting_up = self.append(ir.Compare(ast.Gt(loc=None), step,
ir.Constant(0, step.type)))
unstepped_size = self.append(ir.Arith(ast.Sub(loc=None),
mapped_stop_index, mapped_start_index))
slice_size_a = self.append(ir.Arith(ast.FloorDiv(loc=None), unstepped_size, step))
slice_size_b = self.append(ir.Arith(ast.Mod(loc=None), unstepped_size, step))
rem_not_empty = self.append(ir.Compare(ast.NotEq(loc=None), slice_size_b,
ir.Constant(0, slice_size_b.type)))
slice_size_c = self.append(ir.Arith(ast.Add(loc=None), slice_size_a,
ir.Constant(1, slice_size_a.type)))
slice_size = self.append(ir.Select(rem_not_empty,
slice_size_c, slice_size_a,
name="slice.size"))
self._make_check(
self.append(ir.Compare(ast.NotEq(loc=None), step, ir.Constant(0, step.type))),
lambda: self.alloc_exn(builtins.TException("ValueError"),
ir.Constant("step cannot be zero", builtins.TStr())),
loc=node.slice.step.loc)
else:
step = ir.Constant(1, node.slice.type)
counting_up = self.append(ir.Compare(ast.Gt(loc=None), step,
ir.Constant(0, step.type)))
self.append(ir.Compare(ast.LtE(loc=None), slice_size, length)),
lambda slice_size, length: self.alloc_exn(builtins.TException("ValueError"),
ir.Constant("slice size {0} is larger than iterable length {1}",
builtins.TStr()),
slice_size, length),
params=[slice_size, length],
loc=node.slice.loc)
unstepped_size = self.append(ir.Arith(ast.Sub(loc=None),
mapped_stop_index, mapped_start_index))
slice_size_a = self.append(ir.Arith(ast.FloorDiv(loc=None), unstepped_size, step))
slice_size_b = self.append(ir.Arith(ast.Mod(loc=None), unstepped_size, step))
rem_not_empty = self.append(ir.Compare(ast.NotEq(loc=None), slice_size_b,
ir.Constant(0, slice_size_b.type)))
slice_size_c = self.append(ir.Arith(ast.Add(loc=None), slice_size_a,
ir.Constant(1, slice_size_a.type)))
slice_size = self.append(ir.Select(rem_not_empty,
slice_size_c, slice_size_a,
name="slice.size"))
self._make_check(
self.append(ir.Compare(ast.LtE(loc=None), slice_size, length)),
lambda slice_size, length: self.alloc_exn(builtins.TException("ValueError"),
ir.Constant("slice size {0} is larger than iterable length {1}",
builtins.TStr()),
slice_size, length),
params=[slice_size, length],
loc=node.slice.loc)
if self.current_assign is None:
is_neg_size = self.append(ir.Compare(ast.Lt(loc=None),
slice_size, ir.Constant(0, slice_size.type)))
abs_slice_size = self.append(ir.Select(is_neg_size,
ir.Constant(0, slice_size.type), slice_size))
other_value = self.append(ir.Alloc([abs_slice_size], value.type,
name="slice.result"))
else:
other_value = self.current_assign
if self.current_assign is None:
is_neg_size = self.append(ir.Compare(ast.Lt(loc=None),
slice_size, ir.Constant(0, slice_size.type)))
abs_slice_size = self.append(ir.Select(is_neg_size,
ir.Constant(0, slice_size.type), slice_size))
other_value = self.append(ir.Alloc([abs_slice_size], value.type,
name="slice.result"))
else:
other_value = self.current_assign
prehead = self.current_block
prehead = self.current_block
head = self.current_block = self.add_block("slice.head")
prehead.append(ir.Branch(head))
head = self.current_block = self.add_block("slice.head")
prehead.append(ir.Branch(head))
index = self.append(ir.Phi(node.slice.type,
name="slice.index"))
index.add_incoming(mapped_start_index, prehead)
other_index = self.append(ir.Phi(node.slice.type,
name="slice.resindex"))
other_index.add_incoming(ir.Constant(0, node.slice.type), prehead)
index = self.append(ir.Phi(node.slice.type,
name="slice.index"))
index.add_incoming(mapped_start_index, prehead)
other_index = self.append(ir.Phi(node.slice.type,
name="slice.resindex"))
other_index.add_incoming(ir.Constant(0, node.slice.type), prehead)
# Still within bounds?
bounded_up = self.append(ir.Compare(ast.Lt(loc=None), index, mapped_stop_index))
bounded_down = self.append(ir.Compare(ast.Gt(loc=None), index, mapped_stop_index))
within_bounds = self.append(ir.Select(counting_up, bounded_up, bounded_down))
# Still within bounds?
bounded_up = self.append(ir.Compare(ast.Lt(loc=None), index, mapped_stop_index))
bounded_down = self.append(ir.Compare(ast.Gt(loc=None), index, mapped_stop_index))
within_bounds = self.append(ir.Select(counting_up, bounded_up, bounded_down))
body = self.current_block = self.add_block("slice.body")
body = self.current_block = self.add_block("slice.body")
if self.current_assign is None:
elem = self.iterable_get(value, index)
self.append(ir.SetElem(other_value, other_index, elem))
else:
elem = self.append(ir.GetElem(self.current_assign, other_index))
self.append(ir.SetElem(value, index, elem))
if self.current_assign is None:
elem = self.iterable_get(value, index)
self.append(ir.SetElem(other_value, other_index, elem))
else:
elem = self.append(ir.GetElem(self.current_assign, other_index))
self.append(ir.SetElem(value, index, elem))
next_index = self.append(ir.Arith(ast.Add(loc=None), index, step))
index.add_incoming(next_index, body)
next_other_index = self.append(ir.Arith(ast.Add(loc=None), other_index,
ir.Constant(1, node.slice.type)))
other_index.add_incoming(next_other_index, body)
self.append(ir.Branch(head))
next_index = self.append(ir.Arith(ast.Add(loc=None), index, step))
index.add_incoming(next_index, body)
next_other_index = self.append(ir.Arith(ast.Add(loc=None), other_index,
ir.Constant(1, node.slice.type)))
other_index.add_incoming(next_other_index, body)
self.append(ir.Branch(head))
tail = self.current_block = self.add_block("slice.tail")
head.append(ir.BranchIf(within_bounds, body, tail))
tail = self.current_block = self.add_block("slice.tail")
head.append(ir.BranchIf(within_bounds, body, tail))
if self.current_assign is None:
return other_value
if self.current_assign is None:
return other_value
def visit_TupleT(self, node):
if self.current_assign is None:

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@ -269,6 +269,14 @@ class Inferencer(algorithm.Visitor):
else:
self._unify_iterable(element=node, collection=node.value)
elif isinstance(node.slice, ast.Slice):
if builtins.is_array(node.value.type):
if node.slice.step is not None:
diag = diagnostic.Diagnostic(
"error",
"strided slicing not yet supported for NumPy arrays", {},
node.slice.step.loc, [])
self.engine.process(diag)
return
self._unify(node.type, node.value.type, node.loc, node.value.loc)
else: # ExtSlice
pass # error emitted above

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@ -9,5 +9,8 @@ b = array([1, 2, 3])
# CHECK-L: ${LINE:+1}: error: too many indices for array of dimension 1
b[1, 2]
# CHECK-L: ${LINE:+1}: error: strided slicing not yet supported for NumPy arrays
b[::-1]
# CHECK-L: ${LINE:+1}: error: array attributes cannot be assigned to
b.shape = (5, )

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@ -0,0 +1,24 @@
# RUN: %python -m artiq.compiler.testbench.jit %s
a = array([0, 1, 2, 3])
b = a[2:3]
assert b.shape == (1,)
assert b[0] == 2
b[0] = 5
assert a[2] == 5
b = a[3:2]
assert b.shape == (0,)
c = array([[0, 1], [2, 3]])
d = c[:1]
assert d.shape == (1, 2)
assert d[0, 0] == 0
assert d[0, 1] == 1
d[0, 0] = 5
assert c[0, 0] == 5
d = c[1:0]
assert d.shape == (0, 2)

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@ -0,0 +1,13 @@
# RUN: %python -m artiq.compiler.testbench.embedding %s
from artiq.language.core import *
from artiq.language.types import *
import numpy as np
n = 2
data = np.zeros((n, n))
@kernel
def entrypoint():
print(data[:n])