TensorExt

’tensor_ext’ Dialect

The tensor_ext dialect contains operations on plaintext tensors that correspond to the computation model of certain FHE schemes, but are unlikely to be upstreamed to MLIR due to their specificity to FHE.

TensorExt attributes

SIMDPackingAttr

An attribute describing the SIMD packing of a tensor.

Syntax:

#tensor_ext.simd_packing<
  ::mlir::DenseI64ArrayAttr,   # in
  ::mlir::DenseI64ArrayAttr,   # padding
  ::mlir::DenseI64ArrayAttr,   # out
  int64_t   # padding_value
>

This attribute is used as the encoding attribute on a tensor. It describes the transformations that were applied to an input tensor to pack it into the given tensor.

The in attribute describes the shape of the original tensor. The following transformations are applied to the input tensor.

1. Padding is applied first. The padding attribute is an array with the same size as the input tensor shape. Padding is applied at the end of the array using the padding_value attribute (default zero). The result after zero padding should be a power of two.

2. The padded result is replicated or split to fill the output tensor shape.

For example,

#packing = #tensor_ext.simd_packing<
  in = [7],
  padding = [1],
  padding_value = 0,
  out = [16],
>

may be used on a tensor type like

tensor<1x16xi32, #packing>

If the original tensor had values [1, 2, 3, 4, 5, 6, 7] then a tensor with this attribute contains the data [1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 0].

Parameters:

TensorExt ops

tensor_ext.convert_layout (heir::tensor_ext::ConvertLayoutOp)

Convert from one layout to another.

Syntax:

operation ::= `tensor_ext.convert_layout` operands attr-dict `:` type($output)

This op represents the conversion of a tensor from one packed layout to another. This is implemented via a “shift network” of ciphertext rotations, plaintext masks (ciphertext-plaintext multiplications), and additions.

This op is inserted by layout selection passes.

Traits: AlwaysSpeculatableImplTrait

Interfaces: ConditionallySpeculatable, InferTypeOpInterface, NoMemoryEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Attributes:

Operands:

Results:

tensor_ext.rotate (heir::tensor_ext::RotateOp)

Rotate a tensor some number of indices left.

Syntax:

operation ::= `tensor_ext.rotate` operands attr-dict `:` qualified(type($tensor)) `,` type($shift)

This op represents a left-rotation of a tensor by given number of indices. Negative shift values are interpreted as right-rotations.

This corresponds to the rotate operation in arithmetic FHE schemes like BGV.

This operation’s current behavior allows rotating multi-dimensional tensors by rotating along the tensor’s only non-unit dimension. This assumes the tensor is packed along the non-unit dimension.

// In the future, the op will be adjusted to support rotations of general // multi-dimensional tensors with a vector of rotation indices for each // dimension. The lowering will implement the correct operations to rotate // the tensor along the indices given its packing.

Examples:

%0 = ... : tensor<16xi32>
%c7 = arith.constant 7 : i32
%1 = tensor_ext.rotate %0, %c7 : tensor<16xi32>, i32

Traits: AlwaysSpeculatableImplTrait

Interfaces: ConditionallySpeculatable, InferTypeOpInterface, NoMemoryEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Results: