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// Copyright (c) 2018 Google LLC.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "source/opt/licm_pass.h"
#include <queue>
#include "source/opt/module.h"
#include "source/opt/pass.h"
namespace spvtools {
namespace opt {
Pass::Status LICMPass::Process() { return ProcessIRContext(); }
Pass::Status LICMPass::ProcessIRContext() {
Status status = Status::SuccessWithoutChange;
Module* module = get_module();
// Process each function in the module
for (auto func = module->begin();
func != module->end() && status != Status::Failure; ++func) {
status = CombineStatus(status, ProcessFunction(&*func));
}
return status;
}
Pass::Status LICMPass::ProcessFunction(Function* f) {
Status status = Status::SuccessWithoutChange;
LoopDescriptor* loop_descriptor = context()->GetLoopDescriptor(f);
// Process each loop in the function
for (auto it = loop_descriptor->begin();
it != loop_descriptor->end() && status != Status::Failure; ++it) {
Loop& loop = *it;
// Ignore nested loops, as we will process them in order in ProcessLoop
if (loop.IsNested()) {
continue;
}
status = CombineStatus(status, ProcessLoop(&loop, f));
}
return status;
}
Pass::Status LICMPass::ProcessLoop(Loop* loop, Function* f) {
Status status = Status::SuccessWithoutChange;
// Process all nested loops first
for (auto nl = loop->begin(); nl != loop->end() && status != Status::Failure;
++nl) {
Loop* nested_loop = *nl;
status = CombineStatus(status, ProcessLoop(nested_loop, f));
}
std::vector<BasicBlock*> loop_bbs{};
status = CombineStatus(
status,
AnalyseAndHoistFromBB(loop, f, loop->GetHeaderBlock(), &loop_bbs));
for (size_t i = 0; i < loop_bbs.size() && status != Status::Failure; ++i) {
BasicBlock* bb = loop_bbs[i];
// do not delete the element
status =
CombineStatus(status, AnalyseAndHoistFromBB(loop, f, bb, &loop_bbs));
}
return status;
}
Pass::Status LICMPass::AnalyseAndHoistFromBB(
Loop* loop, Function* f, BasicBlock* bb,
std::vector<BasicBlock*>* loop_bbs) {
bool modified = false;
std::function<bool(Instruction*)> hoist_inst =
[this, &loop, &modified](Instruction* inst) {
if (loop->ShouldHoistInstruction(*inst)) {
if (!HoistInstruction(loop, inst)) {
return false;
}
modified = true;
}
return true;
};
if (IsImmediatelyContainedInLoop(loop, f, bb)) {
if (!bb->WhileEachInst(hoist_inst, false)) {
return Status::Failure;
}
}
DominatorAnalysis* dom_analysis = context()->GetDominatorAnalysis(f);
DominatorTree& dom_tree = dom_analysis->GetDomTree();
for (DominatorTreeNode* child_dom_tree_node : *dom_tree.GetTreeNode(bb)) {
if (loop->IsInsideLoop(child_dom_tree_node->bb_)) {
loop_bbs->push_back(child_dom_tree_node->bb_);
}
}
return (modified ? Status::SuccessWithChange : Status::SuccessWithoutChange);
}
bool LICMPass::IsImmediatelyContainedInLoop(Loop* loop, Function* f,
BasicBlock* bb) {
LoopDescriptor* loop_descriptor = context()->GetLoopDescriptor(f);
return loop == (*loop_descriptor)[bb->id()];
}
bool LICMPass::HoistInstruction(Loop* loop, Instruction* inst) {
BasicBlock* pre_header_bb = loop->GetOrCreatePreHeaderBlock();
if (!pre_header_bb) {
return false;
}
Instruction* insertion_point = &*pre_header_bb->tail();
Instruction* previous_node = insertion_point->PreviousNode();
if (previous_node && (previous_node->opcode() == spv::Op::OpLoopMerge ||
previous_node->opcode() == spv::Op::OpSelectionMerge)) {
insertion_point = previous_node;
}
inst->InsertBefore(insertion_point);
context()->set_instr_block(inst, pre_header_bb);
return true;
}
} // namespace opt
} // namespace spvtools
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