MLIR Hello Dialect

This is the minimal example to look into the way to implement the hello-world kind of program with MLIR. The basic code structure is borrowed from standalone and Toy language in LLVM project.

From Third-Party Dev Packages Prequisites

Building

You'll need miniconda on your device for this to work

conda env create -f enviornment.yml && conda activate mlir-conda
mkdir build && cd build
cmake -G 'CodeBlocks - Ninja' -DCMAKE_EXPORT_COMPILE_COMMANDS=ON .. 

cmake --build . --target hello-opt

That's it.

To run the test, check-hello target will be usable. See section below on Lit for this.

To build the documentation from the TableGen description of the dialect operations, run:

cmake --build . --target mlir-doc

OQC Specifics

$ ./build/bin/hello-opt ../test/Hello/oqc.mlir

Converts OQC Dialect into LLVM.

The following shows intermediate IR through all the passes

$ ./bin/hello-opt ../test/Hello/oqc.mlir --mlir-print-ir-after-all

Execution

hello-opt will lower the MLIR into the bytecode of LLVM.

# Lower MLIR to LLVM IR
$ ./build/bin/hello-opt ./test/Hello/print.mlir > /path/to/print.ll

# Execute the code with LLVM interpreter
$ lli /path/to/print.ll 

1.000000 2.000000 3.000000
4.000000 5.000000 6.000000

Lit Checks

The conda layout is not exactly what the testing framework expects. A number of utilities need to be symbolically linked

ln -sf $CONDA_PREFIX/libexec/llvm/not $CONDA_PREFIX/bin
ln -sf $CONDA_PREFIX/libexec/llvm/count $CONDA_PREFIX/bin
ln -sf $CONDA_PREFIX/libexec/llvm/FileCheck $CONDA_PREFIX/bin

Then to run the tests

ninja check-hello

Operations

hello.constant (::hello::ConstantOp)

constant

Constant operation turns a literal into an SSA value. The data is attached to the operation as an attribute. For example:

  %0 = "hello.constant"()
  { value = dense<[[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]]> : tensor<2x3xf64> }
  : () -> tensor<2x3xf64>

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Attributes:

Attribute	MLIR Type	Description
value	::mlir::DenseElementsAttr	64-bit float elements attribute

Results:

Result	Description
«unnamed»	tensor of 64-bit float values

hello.print (::hello::PrintOp)

print operation

Syntax:

operation ::= `hello.print` $input attr-dict `:` type($input)

The "print" builtin operation prints a given input tensor, and produces no results.

Interfaces: NoSideEffect (MemoryEffectOpInterface)

Effects: MemoryEffects::Effect{}

Operands:

Operand	Description
input	tensor of 64-bit float values or memref of 64-bit float values