MLIR Passes

This document describes the available MLIR passes and their contracts.

Affine control lowering (-lower-affine)

Convert instructions related to affine control into a graph of blocks using operations from the standard dialect.

Loop statements are converted to a subgraph of blocks (initialization, condition checking, subgraph of body blocks) with loop induction variable being passed as the block argument of the condition checking block. Conditional statements are converted to a subgraph of blocks (chain of condition checking with short-circuit logic, subgraphs of ‘then’ and ‘else’ body blocks). affine_apply operations are converted into sequences of primitive arithmetic operations that have the same effect, using operands of the index type. Consequently, named maps and sets may be removed from the module.

For example, %r = affine_apply (d0, d1)[s0] -> (d0 + 2*d1 + s0)(%d0, %d1)[%s0] can be converted into:

%d0 = <...>
%d1 = <...>
%s0 = <...>
%0 = constant 2 : index
%1 = muli %0, %d1
%2 = addi %d0, %1
%r = addi %2, %s0

Input invariant

  • no Tensor types;

These restrictions may be lifted in the future.

Output IR

Functions with for and if instructions eliminated. These functions may contain operations from the Standard dialect in addition to those already present before the pass.

Invariants

  • Functions without a body are not modified.
  • The semantics of the other functions is preserved.
  • Individual operations other than those mentioned above are not modified if they do not depend on the loop iterator value or on the result of affine_apply.