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1 // Copyright (c) 2018 Google LLC.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //     http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 
15 #ifndef SOURCE_OPT_LOOP_FISSION_H_
16 #define SOURCE_OPT_LOOP_FISSION_H_
17 
18 #include <algorithm>
19 #include <cstdint>
20 #include <map>
21 #include <utility>
22 #include <vector>
23 
24 #include "source/opt/cfg.h"
25 #include "source/opt/loop_dependence.h"
26 #include "source/opt/loop_utils.h"
27 #include "source/opt/module.h"
28 #include "source/opt/pass.h"
29 #include "source/opt/tree_iterator.h"
30 
31 namespace spvtools {
32 namespace opt {
33 
34 class LoopFissionPass : public Pass {
35  public:
36   // Fuction used to determine if a given loop should be split. Takes register
37   // pressure region for that loop as a parameter and returns true if the loop
38   // should be split.
39   using FissionCriteriaFunction =
40       std::function<bool(const RegisterLiveness::RegionRegisterLiveness&)>;
41 
42   // Pass built with this constructor will split all loops regardless of
43   // register pressure. Will not split loops more than once.
44   LoopFissionPass();
45 
46   // Split the loop if the number of registers used in the loop exceeds
47   // |register_threshold_to_split|. |split_multiple_times| flag determines
48   // whether or not the pass should split loops after already splitting them
49   // once.
50   LoopFissionPass(size_t register_threshold_to_split,
51                   bool split_multiple_times = true);
52 
53   // Split loops whose register pressure meets the criteria of |functor|.
54   LoopFissionPass(FissionCriteriaFunction functor,
55                   bool split_multiple_times = true)
split_criteria_(functor)56       : split_criteria_(functor), split_multiple_times_(split_multiple_times) {}
57 
name()58   const char* name() const override { return "loop-fission"; }
59 
60   Pass::Status Process() override;
61 
62   // Checks if |loop| meets the register pressure criteria to be split.
63   bool ShouldSplitLoop(const Loop& loop, IRContext* context);
64 
65  private:
66   // Functor to run in ShouldSplitLoop to determine if the register pressure
67   // criteria is met for splitting the loop.
68   FissionCriteriaFunction split_criteria_;
69 
70   // Flag designating whether or not we should also split the result of
71   // previously split loops if they meet the register presure criteria.
72   bool split_multiple_times_;
73 };
74 
75 }  // namespace opt
76 }  // namespace spvtools
77 
78 #endif  // SOURCE_OPT_LOOP_FISSION_H_
79