xref: /llvm-project/mlir/include/mlir/Dialect/PDL/IR/PDLDialect.td (revision 863c346209e27d22157fad21d0fd730e710a3441) 
1//===- PDLDialect.td - PDL dialect definition --------------*- tablegen -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// Defines the MLIR PDL dialect.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef MLIR_DIALECT_PDL_IR_PDLDIALECT
14#define MLIR_DIALECT_PDL_IR_PDLDIALECT
15
16include "mlir/IR/OpBase.td"
17
18//===----------------------------------------------------------------------===//
19// PDL Dialect
20//===----------------------------------------------------------------------===//
21
22def PDL_Dialect : Dialect {
23  let summary = "High level pattern definition dialect";
24  let description = [{
25    PDL presents a high level abstraction for the rewrite pattern infrastructure
26    available in MLIR. This abstraction allows for representing patterns
27    transforming MLIR, as MLIR. This allows for applying all of the benefits
28    that the general MLIR infrastructure provides, to the infrastructure itself.
29    This means that pattern matching can be more easily verified for
30    correctness, targeted by frontends, and optimized.
31
32    PDL abstracts over various different aspects of patterns and core MLIR data
33    structures. Patterns are specified via a `pdl.pattern` operation. These
34    operations contain a region body for the "matcher" code, and terminate with
35    a `pdl.rewrite` that either dispatches to an external rewriter or contains
36    a region for the rewrite specified via `pdl`. The types of values in `pdl`
37    are handle types to MLIR C++ types, with `!pdl.attribute`, `!pdl.operation`,
38    `!pdl.value`, and `!pdl.type` directly mapping to `mlir::Attribute`,
39    `mlir::Operation*`, `mlir::Value`, and `mlir::Type` respectively.
40
41    An example pattern is shown below:
42
43    ```mlir
44    // pdl.pattern contains metadata similarly to a `RewritePattern`.
45    pdl.pattern : benefit(1) {
46      // External input operand values are specified via `pdl.operand` operations.
47      // Result types are constrainted via `pdl.type` operations.
48
49      %resultType = pdl.type
50      %inputOperand = pdl.operand
51      %root = pdl.operation "foo.op"(%inputOperand) -> %resultType
52      pdl.rewrite %root {
53        pdl.replace %root with (%inputOperand)
54      }
55    }
56    ```
57
58    The above pattern simply replaces an operation with its first operand. Note
59    how the input operation is specified structurally, similarly to how it would
60    look in memory. This is a simple example and pdl provides support for many
61    other features such as applying external constraints or external generator
62    methods. These features and more are detailed below.
63  }];
64
65  let name = "pdl";
66  let cppNamespace = "::mlir::pdl";
67
68  let useDefaultTypePrinterParser = 1;
69  let extraClassDeclaration = [{
70    void registerTypes();
71  }];
72}
73
74#endif // MLIR_DIALECT_PDL_IR_PDLDIALECT
75