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#include "source/opt/loop_fusion_pass.h"
16
17#include "source/opt/ir_context.h"
18#include "source/opt/loop_descriptor.h"
19#include "source/opt/loop_fusion.h"
20#include "source/opt/register_pressure.h"
21
22namespace spvtools {
23namespace opt {
24
25Pass::Status LoopFusionPass::Process() {
26 bool modified = false;
27 Module* module = context()->module();
28
29 // Process each function in the module
30 for (Function& f : *module) {
31 modified |= ProcessFunction(&f);
32 }
33
34 return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
35}
36
37bool LoopFusionPass::ProcessFunction(Function* function) {
38 LoopDescriptor& ld = *context()->GetLoopDescriptor(function);
39
40 // If a loop doesn't have a preheader needs then it needs to be created. Make
41 // sure to return Status::SuccessWithChange in that case.
42 auto modified = ld.CreatePreHeaderBlocksIfMissing();
43
44 // TODO(tremmelg): Could the only loop that |loop| could possibly be fused be
45 // picked out so don't have to check every loop
46 for (auto& loop_0 : ld) {
47 for (auto& loop_1 : ld) {
48 LoopFusion fusion(context(), &loop_0, &loop_1);
49
50 if (fusion.AreCompatible() && fusion.IsLegal()) {
51 RegisterLiveness liveness(context(), function);
52 RegisterLiveness::RegionRegisterLiveness reg_pressure{};
53 liveness.SimulateFusion(loop_0, loop_1, &reg_pressure);
54
55 if (reg_pressure.used_registers_ <= max_registers_per_loop_) {
56 fusion.Fuse();
57 // Recurse, as the current iterators will have been invalidated.
58 ProcessFunction(function);
59 return true;
60 }
61 }
62 }
63 }
64
65 return modified;
66}
67
68} // namespace opt
69} // namespace spvtools
70