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[FFI] Make StructuralEqual functor compare tensor content #646

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[FFI] Make StructuralEqual functor compare tensor content #646

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[FFI] Make StructuralEqual functor compare tensor content
pisarev Jun 26, 2026
66b381b
[FFI] Add regression test for StructuralEqual tensor content
pisarev Jun 26, 2026
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2 changes: 1 addition & 1 deletion include/tvm/ffi/extra/structural_equal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,7 @@ class StructuralEqual {
* \return True if the two Any values are structurally equal, false otherwise.
*/
TVM_FFI_INLINE bool operator()(const Any& lhs, const Any& rhs) const {
return Equal(lhs, rhs, false, true);
return Equal(lhs, rhs, false, false);

@gemini-code-assist gemini-code-assist Bot Jun 26, 2026

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medium

Passing multiple consecutive boolean literals (often referred to as the "Boolean Trap") reduces code readability and increases the risk of parameter mismatch errors. Since both map_free_vars and skip_tensor_content default to false in the signature of Equal, we can simplify this call to Equal(lhs, rhs) to make the code cleaner and more maintainable.

    return Equal(lhs, rhs);

}
};

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40 changes: 40 additions & 0 deletions tests/cpp/extra/test_structural_equal_hash.cc
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Expand Up @@ -22,6 +22,7 @@
#include <tvm/ffi/container/dict.h>
#include <tvm/ffi/container/list.h>
#include <tvm/ffi/container/map.h>
#include <tvm/ffi/container/tensor.h>
#include <tvm/ffi/extra/structural_equal.h>
#include <tvm/ffi/extra/structural_hash.h>
#include <tvm/ffi/object.h>
Expand All @@ -36,6 +37,21 @@ using namespace tvm::ffi;
using namespace tvm::ffi::testing;
namespace refl = tvm::ffi::reflection;

// CPU allocator and a helper to build a 1-D float32 tensor filled with one
// value, like test_tensor.cc does.
struct CPUNDAlloc {
void AllocData(DLTensor* tensor) { tensor->data = malloc(GetDataSize(*tensor)); }
void FreeData(DLTensor* tensor) { free(tensor->data); }
};

Tensor MakeFilledTensor(const Shape& shape, float value) {
Tensor t = Tensor::FromNDAlloc(CPUNDAlloc(), shape, DLDataType({kDLFloat, 32, 1}),
DLDevice({kDLCPU, 0}));
float* dst = reinterpret_cast<float*>(t.data_ptr());
for (int64_t i = 0; i < t.numel(); ++i) dst[i] = value;
return t;
}

TEST(StructuralEqualHash, Array) {
Array<int> a = {1, 2, 3};
Array<int> b = {1, 2, 3};
Expand Down Expand Up @@ -333,4 +349,28 @@ TEST(StructuralEqualHash, ArraySelfInsertProducesSnapshot) {
EXPECT_EQ(StructuralHash()(arr), StructuralHash()(arr));
}

// Regression test for #645. StructuralHash hashes tensor content, so the
// StructuralEqual functor has to compare content too. Otherwise two distinct
// same-shape constants hash differently but compare equal, which breaks the
// constant de-dup map invariant and can silently merge different weights on a
// bucket collision.
TEST(StructuralEqualHash, TensorContent) {
Tensor zeros = MakeFilledTensor({4}, 0.0f);
Tensor ones = MakeFilledTensor({4}, 1.0f);
Tensor zeros_copy = MakeFilledTensor({4}, 0.0f);

// Different content, same shape and dtype: not equal, and the hash differs.
EXPECT_FALSE(StructuralEqual()(zeros, ones));
EXPECT_NE(StructuralHash()(zeros), StructuralHash()(ones));

// Identical content still compares equal and hashes equal, so real duplicates
// still get merged.
EXPECT_TRUE(StructuralEqual()(zeros, zeros_copy));
EXPECT_EQ(StructuralHash()(zeros), StructuralHash()(zeros_copy));

// Skipping content is still available as an explicit opt-in.
EXPECT_TRUE(StructuralEqual::Equal(zeros, ones, /*map_free_vars=*/false,
/*skip_tensor_content=*/true));
}

} // namespace
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