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