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https://github.com/KhronosGroup/SPIRV-Tools
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82663f34c9
Merge return assumes that the only unreachable blocks are those needed to keep the structured cfg valid. Even those must be essentially empty blocks. If this is not the case, we get unpredictable behaviour. This commit add a check in merge return, and emits an error if it is not the case. Added a pass of dead branch elimination before merge return in both the performance and size passes. It is a precondition of merge return. Fixes #1962.
129 lines
3.7 KiB
C++
129 lines
3.7 KiB
C++
// Copyright (c) 2018 Google LLC.
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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 "source/opt/struct_cfg_analysis.h"
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#include "source/opt/ir_context.h"
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namespace {
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const uint32_t kMergeNodeIndex = 0;
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const uint32_t kContinueNodeIndex = 1;
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}
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namespace spvtools {
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namespace opt {
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StructuredCFGAnalysis::StructuredCFGAnalysis(IRContext* ctx) : context_(ctx) {
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// If this is not a shader, there are no merge instructions, and not
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// structured CFG to analyze.
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if (!context_->get_feature_mgr()->HasCapability(SpvCapabilityShader)) {
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return;
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}
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for (auto& func : *context_->module()) {
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AddBlocksInFunction(&func);
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}
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}
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void StructuredCFGAnalysis::AddBlocksInFunction(Function* func) {
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std::list<BasicBlock*> order;
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context_->cfg()->ComputeStructuredOrder(func, &*func->begin(), &order);
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struct TraversalInfo {
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ConstructInfo cinfo;
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uint32_t merge_node;
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};
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// Set up a stack to keep track of currently active constructs.
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std::vector<TraversalInfo> state;
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state.emplace_back();
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state[0].cinfo.containing_construct = 0;
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state[0].cinfo.containing_loop = 0;
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state[0].merge_node = 0;
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for (BasicBlock* block : order) {
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if (context_->cfg()->IsPseudoEntryBlock(block) ||
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context_->cfg()->IsPseudoExitBlock(block)) {
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continue;
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}
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if (block->id() == state.back().merge_node) {
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state.pop_back();
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}
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bb_to_construct_.emplace(std::make_pair(block->id(), state.back().cinfo));
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if (Instruction* merge_inst = block->GetMergeInst()) {
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TraversalInfo new_state;
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new_state.merge_node =
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merge_inst->GetSingleWordInOperand(kMergeNodeIndex);
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new_state.cinfo.containing_construct = block->id();
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if (merge_inst->opcode() == SpvOpLoopMerge) {
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new_state.cinfo.containing_loop = block->id();
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} else {
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new_state.cinfo.containing_loop = state.back().cinfo.containing_loop;
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}
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state.emplace_back(new_state);
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merge_blocks_.Set(new_state.merge_node);
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}
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}
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}
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uint32_t StructuredCFGAnalysis::MergeBlock(uint32_t bb_id) {
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uint32_t header_id = ContainingConstruct(bb_id);
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if (header_id == 0) {
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return 0;
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}
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BasicBlock* header = context_->cfg()->block(header_id);
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Instruction* merge_inst = header->GetMergeInst();
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return merge_inst->GetSingleWordInOperand(kMergeNodeIndex);
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}
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uint32_t StructuredCFGAnalysis::LoopMergeBlock(uint32_t bb_id) {
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uint32_t header_id = ContainingLoop(bb_id);
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if (header_id == 0) {
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return 0;
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}
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BasicBlock* header = context_->cfg()->block(header_id);
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Instruction* merge_inst = header->GetMergeInst();
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return merge_inst->GetSingleWordInOperand(kMergeNodeIndex);
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}
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uint32_t StructuredCFGAnalysis::LoopContinueBlock(uint32_t bb_id) {
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uint32_t header_id = ContainingLoop(bb_id);
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if (header_id == 0) {
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return 0;
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}
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BasicBlock* header = context_->cfg()->block(header_id);
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Instruction* merge_inst = header->GetMergeInst();
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return merge_inst->GetSingleWordInOperand(kContinueNodeIndex);
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}
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bool StructuredCFGAnalysis::IsContinueBlock(uint32_t bb_id) {
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assert(bb_id != 0);
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return LoopContinueBlock(bb_id) == bb_id;
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}
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bool StructuredCFGAnalysis::IsMergeBlock(uint32_t bb_id) {
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return merge_blocks_.Get(bb_id);
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}
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} // namespace opt
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} // namespace spvtools
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