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IREE / MLIR / Linalg tutorial


This tutorial is simultaneously about IREE, MLIR, and specifically the MLIR Linalg dialect.

What is MLIR?

MLIR is a programming language, but MLIR in itself is almost just an empty shell. What it really provides is a framework allowing to define MLIR dialects which are where the features come from.

The "IR" part of the MLIR name stands for "intermediate representation". It means that MLIR is meant to be primarily for compiler-internal representations of code. But MLIR is actually fairly nice for humans to work with, and it's not hard to hand-author some MLIR programs from scratch. That is exactly the topic of this tutorial.

Exploring CPU microkernels on a matmul example

Basic setup, command lines

Source file: matmul.mlir:

func.func @matmul_dynamic(%lhs: tensor<?x?xf32>, %rhs: tensor<?x?xf32>, %acc: tensor<?x?xf32>) -> tensor<?x?xf32> {
  %result = linalg.matmul ins(%lhs, %rhs: tensor<?x?xf32>, tensor<?x?xf32>) outs(%acc: tensor<?x?xf32>) -> tensor<?x?xf32>
  return %result: tensor<?x?xf32>

Basic compilation command line:

$ iree-compile matmul.mlir -o /tmp/matmul.vmfb \
  --iree-hal-target-backends=llvm-cpu \
  --iree-llvmcpu-target-cpu=znver4 \

This creates a IREE bytecode module:

$ ls -l /tmp/matmul.vmfb

-rw-rw-r-- 1 2884 Jan 22 10:37 /tmp/matmul.vmfb