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https://github.com/KhronosGroup/SPIRV-Tools
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4fcdc58946
There was a lot of code in the codebase that would get the dominator analysis for a function and then use it to check whether a block is reachable. In the fuzzer, a utility method had been introduced to make this more concise, but it was not being used consistently. This change moves the utility method to IRContext, so that it can be used throughout the codebase, and refactors all existing checks for block reachability to use the utility method.
192 lines
8.0 KiB
C++
192 lines
8.0 KiB
C++
// Copyright (c) 2021 Alastair F. Donaldson
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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/fuzz/available_instructions.h"
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#include "source/fuzz/fuzzer_util.h"
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namespace spvtools {
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namespace fuzz {
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AvailableInstructions::AvailableInstructions(
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opt::IRContext* ir_context,
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const std::function<bool(opt::IRContext*, opt::Instruction*)>& predicate)
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: ir_context_(ir_context) {
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// Consider all global declarations
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for (auto& global : ir_context->module()->types_values()) {
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if (predicate(ir_context, &global)) {
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available_globals_.push_back(&global);
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}
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}
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// Consider every function
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for (auto& function : *ir_context->module()) {
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// Identify those function parameters that satisfy the predicate.
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std::vector<opt::Instruction*> available_params_for_function;
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function.ForEachParam(
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[&predicate, ir_context,
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&available_params_for_function](opt::Instruction* param) {
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if (predicate(ir_context, param)) {
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available_params_for_function.push_back(param);
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}
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});
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// Consider every reachable block in the function.
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auto dominator_analysis = ir_context->GetDominatorAnalysis(&function);
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for (auto& block : function) {
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if (!ir_context->IsReachable(block)) {
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// The block is not reachable.
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continue;
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}
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if (&block == &*function.begin()) {
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// The function entry block is special: only the relevant globals and
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// function parameters are available at its entry point.
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num_available_at_block_entry_.insert(
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{&block,
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static_cast<uint32_t>(available_params_for_function.size() +
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available_globals_.size())});
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} else {
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// |block| is not the entry block and is reachable, so it must have an
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// immediate dominator. The number of instructions available on entry to
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// |block| is thus the number of instructions available on entry to the
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// immediate dominator + the number of instructions generated_by_block
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// by the immediate dominator.
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auto immediate_dominator =
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dominator_analysis->ImmediateDominator(&block);
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assert(immediate_dominator != nullptr &&
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"The block is reachable so should have an immediate dominator.");
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assert(generated_by_block_.count(immediate_dominator) != 0 &&
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"Immediate dominator should have already been processed.");
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assert(num_available_at_block_entry_.count(immediate_dominator) != 0 &&
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"Immediate dominator should have already been processed.");
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num_available_at_block_entry_.insert(
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{&block,
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static_cast<uint32_t>(
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generated_by_block_.at(immediate_dominator).size()) +
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num_available_at_block_entry_.at(immediate_dominator)});
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}
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// Now consider each instruction in the block.
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std::vector<opt::Instruction*> generated_by_block;
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for (auto& inst : block) {
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assert(num_available_at_block_entry_.count(&block) != 0 &&
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"Block should have already been processed.");
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// The number of available instructions before |inst| is the number
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// available at the start of the block + the number of relevant
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// instructions generated by the block so far.
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num_available_before_instruction_.insert(
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{&inst, num_available_at_block_entry_.at(&block) +
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static_cast<uint32_t>(generated_by_block.size())});
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if (predicate(ir_context, &inst)) {
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// This instruction satisfies the predicate, so note that it is
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// generated by |block|.
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generated_by_block.push_back(&inst);
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}
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}
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generated_by_block_.emplace(&block, std::move(generated_by_block));
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}
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available_params_.emplace(&function,
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std::move(available_params_for_function));
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}
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}
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AvailableInstructions::AvailableBeforeInstruction
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AvailableInstructions::GetAvailableBeforeInstruction(
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opt::Instruction* inst) const {
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assert(num_available_before_instruction_.count(inst) != 0 &&
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"Availability can only be queried for reachable instructions.");
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return {*this, inst};
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}
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AvailableInstructions::AvailableBeforeInstruction::AvailableBeforeInstruction(
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const AvailableInstructions& available_instructions, opt::Instruction* inst)
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: available_instructions_(available_instructions), inst_(inst) {}
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uint32_t AvailableInstructions::AvailableBeforeInstruction::size() const {
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return available_instructions_.num_available_before_instruction_.at(inst_);
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}
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bool AvailableInstructions::AvailableBeforeInstruction::empty() const {
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return size() == 0;
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}
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opt::Instruction* AvailableInstructions::AvailableBeforeInstruction::operator[](
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uint32_t index) const {
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assert(index < size() && "Index out of bounds.");
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// First, check the cache to see whether we can return the available
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// instruction in constant time.
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auto cached_result = index_cache.find(index);
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if (cached_result != index_cache.end()) {
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return cached_result->second;
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}
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// Next check whether the index falls into the global region.
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if (index < available_instructions_.available_globals_.size()) {
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auto result = available_instructions_.available_globals_[index];
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index_cache.insert({index, result});
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return result;
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}
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auto block = available_instructions_.ir_context_->get_instr_block(inst_);
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auto function = block->GetParent();
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// Next check whether the index falls into the available instructions that
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// correspond to function parameters.
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if (index <
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available_instructions_.available_globals_.size() +
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available_instructions_.available_params_.at(function).size()) {
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auto result = available_instructions_.available_params_.at(
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function)[index - available_instructions_.available_globals_.size()];
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index_cache.insert({index, result});
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return result;
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}
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auto dominator_analysis =
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available_instructions_.ir_context_->GetDominatorAnalysis(function);
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// Now the expensive part (which is why we have the cache): walk the dominator
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// tree backwards starting from the block containing |inst_| until we get to
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// the block in which the instruction corresponding to |index| exists.
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for (auto* ancestor = block; true;
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ancestor = dominator_analysis->ImmediateDominator(ancestor)) {
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uint32_t num_available_at_ancestor_entry =
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available_instructions_.num_available_at_block_entry_.at(ancestor);
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if (index_cache.count(num_available_at_ancestor_entry) == 0) {
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// This is the first time we have traversed this block, so we populate the
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// cache with the index of each instruction, so that if a future index
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// query relates to indices associated with this block we can return the
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// result in constant time.
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auto& generated_by_ancestor =
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available_instructions_.generated_by_block_.at(ancestor);
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for (uint32_t local_index = 0; local_index < generated_by_ancestor.size();
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local_index++) {
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index_cache.insert({num_available_at_ancestor_entry + local_index,
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generated_by_ancestor[local_index]});
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}
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}
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if (index >= num_available_at_ancestor_entry) {
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// This block contains the instruction we want, so by now it will be in
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// the cache.
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return index_cache.at(index);
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}
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assert(ancestor != &*function->begin() &&
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"By construction we should find a block associated with the index.");
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}
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assert(false && "Unreachable.");
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return nullptr;
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}
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} // namespace fuzz
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} // namespace spvtools
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