2017-12-21 14:47:25 +00:00
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// Copyright (c) 2017 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "opt/loop_descriptor.h"
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#include <iostream>
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#include <type_traits>
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#include <utility>
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#include <vector>
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2018-01-25 10:33:06 +00:00
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#include "opt/cfg.h"
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#include "opt/dominator_tree.h"
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#include "opt/ir_context.h"
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2017-12-21 14:47:25 +00:00
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#include "opt/iterator.h"
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#include "opt/loop_descriptor.h"
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#include "opt/make_unique.h"
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#include "opt/tree_iterator.h"
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namespace spvtools {
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namespace ir {
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Loop::Loop(IRContext* context, opt::DominatorAnalysis* dom_analysis,
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BasicBlock* header, BasicBlock* continue_target,
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BasicBlock* merge_target)
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: loop_header_(header),
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loop_continue_(continue_target),
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loop_merge_(merge_target),
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loop_preheader_(nullptr),
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parent_(nullptr) {
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assert(context);
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assert(dom_analysis);
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loop_preheader_ = FindLoopPreheader(context, dom_analysis);
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AddBasicBlockToLoop(header);
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AddBasicBlockToLoop(continue_target);
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}
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BasicBlock* Loop::FindLoopPreheader(IRContext* ir_context,
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opt::DominatorAnalysis* dom_analysis) {
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CFG* cfg = ir_context->cfg();
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opt::DominatorTree& dom_tree = dom_analysis->GetDomTree();
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opt::DominatorTreeNode* header_node = dom_tree.GetTreeNode(loop_header_);
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// The loop predecessor.
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BasicBlock* loop_pred = nullptr;
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auto header_pred = cfg->preds(loop_header_->id());
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for (uint32_t p_id : header_pred) {
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opt::DominatorTreeNode* node = dom_tree.GetTreeNode(p_id);
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if (node && !dom_tree.Dominates(header_node, node)) {
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// The predecessor is not part of the loop, so potential loop preheader.
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if (loop_pred && node->bb_ != loop_pred) {
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// If we saw 2 distinct predecessors that are outside the loop, we don't
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// have a loop preheader.
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return nullptr;
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}
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loop_pred = node->bb_;
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}
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}
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// Safe guard against invalid code, SPIR-V spec forbids loop with the entry
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// node as header.
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assert(loop_pred && "The header node is the entry block ?");
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// So we have a unique basic block that can enter this loop.
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// If this loop is the unique successor of this block, then it is a loop
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// preheader.
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bool is_preheader = true;
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uint32_t loop_header_id = loop_header_->id();
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loop_pred->ForEachSuccessorLabel(
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[&is_preheader, loop_header_id](const uint32_t id) {
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if (id != loop_header_id) is_preheader = false;
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});
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if (is_preheader) return loop_pred;
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return nullptr;
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}
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2018-01-25 10:33:06 +00:00
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bool Loop::IsInsideLoop(Instruction* inst) const {
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const BasicBlock* parent_block = inst->context()->get_instr_block(inst);
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if (!parent_block) return false;
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return IsInsideLoop(parent_block);
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}
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bool Loop::IsBasicBlockInLoopSlow(const BasicBlock* bb) {
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assert(bb->GetParent() && "The basic block does not belong to a function");
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IRContext* context = bb->GetParent()->GetParent()->context();
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opt::DominatorAnalysis* dom_analysis =
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context->GetDominatorAnalysis(bb->GetParent(), *context->cfg());
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if (!dom_analysis->Dominates(GetHeaderBlock(), bb)) return false;
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opt::PostDominatorAnalysis* postdom_analysis =
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context->GetPostDominatorAnalysis(bb->GetParent(), *context->cfg());
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if (!postdom_analysis->Dominates(GetMergeBlock(), bb)) return false;
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return true;
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}
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2017-12-21 14:47:25 +00:00
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LoopDescriptor::LoopDescriptor(const Function* f) { PopulateList(f); }
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void LoopDescriptor::PopulateList(const Function* f) {
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IRContext* context = f->GetParent()->context();
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opt::DominatorAnalysis* dom_analysis =
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context->GetDominatorAnalysis(f, *context->cfg());
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loops_.clear();
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// Post-order traversal of the dominator tree to find all the OpLoopMerge
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// instructions.
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opt::DominatorTree& dom_tree = dom_analysis->GetDomTree();
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for (opt::DominatorTreeNode& node :
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ir::make_range(dom_tree.post_begin(), dom_tree.post_end())) {
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Instruction* merge_inst = node.bb_->GetLoopMergeInst();
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if (merge_inst) {
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// The id of the merge basic block of this loop.
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uint32_t merge_bb_id = merge_inst->GetSingleWordOperand(0);
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// The id of the continue basic block of this loop.
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uint32_t continue_bb_id = merge_inst->GetSingleWordOperand(1);
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// The merge target of this loop.
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BasicBlock* merge_bb = context->cfg()->block(merge_bb_id);
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// The continue target of this loop.
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BasicBlock* continue_bb = context->cfg()->block(continue_bb_id);
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// The basic block containing the merge instruction.
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BasicBlock* header_bb = context->get_instr_block(merge_inst);
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// Add the loop to the list of all the loops in the function.
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loops_.emplace_back(MakeUnique<Loop>(context, dom_analysis, header_bb,
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continue_bb, merge_bb));
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Loop* current_loop = loops_.back().get();
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// We have a bottom-up construction, so if this loop has nested-loops,
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// they are by construction at the tail of the loop list.
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for (auto itr = loops_.rbegin() + 1; itr != loops_.rend(); ++itr) {
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Loop* previous_loop = itr->get();
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// If the loop already has a parent, then it has been processed.
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if (previous_loop->HasParent()) continue;
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// If the current loop does not dominates the previous loop then it is
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// not nested loop.
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if (!dom_analysis->Dominates(header_bb,
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previous_loop->GetHeaderBlock()))
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continue;
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// If the current loop merge dominates the previous loop then it is
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// not nested loop.
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if (dom_analysis->Dominates(merge_bb, previous_loop->GetHeaderBlock()))
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continue;
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current_loop->AddNestedLoop(previous_loop);
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}
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opt::DominatorTreeNode* dom_merge_node = dom_tree.GetTreeNode(merge_bb);
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for (opt::DominatorTreeNode& loop_node :
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make_range(node.df_begin(), node.df_end())) {
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// Check if we are in the loop.
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if (dom_tree.Dominates(dom_merge_node, &loop_node)) continue;
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current_loop->AddBasicBlockToLoop(loop_node.bb_);
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basic_block_to_loop_.insert(
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std::make_pair(loop_node.bb_->id(), current_loop));
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}
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}
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}
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for (std::unique_ptr<Loop>& loop : loops_) {
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if (!loop->HasParent()) dummy_top_loop_.nested_loops_.push_back(loop.get());
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}
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}
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} // namespace ir
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} // namespace spvtools
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