1/* Copyright 2017 The TensorFlow Authors. All Rights Reserved.
2
3Licensed under the Apache License, Version 2.0 (the "License");
4you may not use this file except in compliance with the License.
5You may obtain a copy of the License at
6
7    http://www.apache.org/licenses/LICENSE-2.0
8
9Unless required by applicable law or agreed to in writing, software
10distributed under the License is distributed on an "AS IS" BASIS,
11WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12See the License for the specific language governing permissions and
13limitations under the License.
14==============================================================================*/
15
16#ifndef TENSORFLOW_COMPILER_XLA_SERVICE_LLVM_IR_LOOP_EMITTER_H_
17#define TENSORFLOW_COMPILER_XLA_SERVICE_LLVM_IR_LOOP_EMITTER_H_
18
19#include <functional>
20
21#include "llvm/IR/BasicBlock.h"
22#include "llvm/IR/IRBuilder.h"
23#include "llvm/IR/Value.h"
24#include "tensorflow/compiler/xla/service/llvm_ir/ir_array.h"
25#include "tensorflow/compiler/xla/statusor.h"
26
27namespace xla {
28namespace llvm_ir {
29
30// A function type for emitting code that generates an element in the target
31// array. The function gets a multi-dimensional index as its only input. This
32// index specifies the target element for which a value needs to be computed.
33// The function has to emit code to compute this value and return the resulting
34// llvm::Value*.
35using ElementGenerator =
36    std::function<StatusOr<llvm::Value*>(const IrArray::Index& index)>;
37
38// Emits a loop for every element in the given shape.
39class LoopEmitter {
40 public:
41  using BodyEmitter =
42      std::function<tensorflow::Status(const IrArray::Index& index)>;
43
44  LoopEmitter(const BodyEmitter& body_emitter, const Shape& shape,
45              llvm::IRBuilder<>* ir_builder);
46  // Constructs a LoopEmitter from an element generator that generates each
47  // element of the given target array.
48  LoopEmitter(const ElementGenerator& target_element_generator,
49              const IrArray& target_array, llvm::IRBuilder<>* ir_builder);
50
51  // Constructs a LoopEmitter that emits one element into each of N separate
52  // arrays on each iteration of the loop.
53  //
54  // This is used for multi-output fusion.  target_element_generator must
55  // produce an LLVM struct with N elements.
56  LoopEmitter(const ElementGenerator& target_element_generator,
57              tensorflow::gtl::ArraySlice<IrArray> target_arrays,
58              llvm::IRBuilder<>* ir_builder);
59
60  LoopEmitter(const LoopEmitter&) = delete;
61  LoopEmitter& operator=(const LoopEmitter&) = delete;
62  virtual ~LoopEmitter() = default;
63
64  // Emits a loop nest (with a yet-to-be-filled loop body) that iterates through
65  // every element in the given shape. Returns the multi-dimensional index that
66  // specifies the element.
67  IrArray::Index EmitIndexAndSetExitBasicBlock() {
68    return EmitIndexAndSetExitBasicBlock(/*loop_name=*/"");
69  }
70  virtual IrArray::Index EmitIndexAndSetExitBasicBlock(
71      tensorflow::StringPiece loop_name);
72
73  // Emits a complete loop nest for every element in the given shape.
74  tensorflow::Status EmitLoop(tensorflow::StringPiece loop_name = "");
75
76 protected:
77  // An IR emitter that generates the loop body.
78  BodyEmitter body_emitter_;
79
80  // The shape that the emitted loop iterates through.
81  Shape shape_;
82
83  // Points to the exit block of the emitted loop. If the given shape is
84  // scalar, no loops are emitted and exit_bb_ is nullptr in that case.
85  llvm::BasicBlock* exit_bb_;
86
87  llvm::IRBuilder<>* ir_builder_;
88};
89
90}  // namespace llvm_ir
91}  // namespace xla
92
93#endif  // TENSORFLOW_COMPILER_XLA_SERVICE_LLVM_IR_LOOP_EMITTER_H_
94