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api: materialise a strided view before assigning into it #3729

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api: materialise a strided view before assigning into it #3729

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5 changes: 5 additions & 0 deletions src/api/c/assign.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,11 @@ static void assign(Array<Tout>& out, const vector<af_seq> seqs,

out.eval();

// createSubArray copies a non-linear parent before slicing it, so a write
// through the slice would land in a temporary and be lost (#3534).
// Materialise the output as a linear array first.
if (!out.isLinear()) { out = copyArray(out); }

dim4 oDims = toDims(seqs, outDs);

bool isVec = true;
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24 changes: 24 additions & 0 deletions test/assign.cpp
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Expand Up @@ -1037,3 +1037,27 @@ TEST(Index, ISSUE_2533) {

ASSERT_VEC_ARRAY_EQ(gold, dim4(5, 10), a);
}

// Assigning into an array that is itself a strided view of a larger buffer
// (here the first four rows of a 5x5) silently did nothing, because the
// write went into a temporary copy of the view.
TEST(Assign, IntoStridedView_ISSUE_3534) {
array a = af::range(dim4(5, 5));
a = a.rows(0, 3);
a(0, 0) = 1234;
ASSERT_EQ(1234.f, a.scalar<float>());

array b = af::range(dim4(5, 5));
b = b.rows(1, 3);
b(span, 2) = constant(-1, 3, 1);
vector<float> h(b.elements());
b.host(h.data());
for (int i = 0; i < 3; i++) { ASSERT_EQ(-1.f, h[i + 2 * 3]) << "row " << i; }
ASSERT_EQ(1.f, h[0]);

array c = af::range(dim4(5, 5));
c = c.rows(0, 3);
array idx = af::seq(0, 1);
c(idx.as(s32), 0) = constant(7, 2, 1);
ASSERT_EQ(7.f, c.scalar<float>());
}
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