mirror of
https://github.com/KhronosGroup/SPIRV-Tools
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252 lines
11 KiB
C++
252 lines
11 KiB
C++
// Copyright (c) 2020 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/fuzz/fuzzer_pass_flatten_conditional_branches.h"
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#include "source/fuzz/comparator_deep_blocks_first.h"
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#include "source/fuzz/instruction_descriptor.h"
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#include "source/fuzz/transformation_flatten_conditional_branch.h"
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namespace spvtools {
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namespace fuzz {
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// A fuzzer pass that randomly selects conditional branches to flatten and
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// flattens them, if possible.
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FuzzerPassFlattenConditionalBranches::FuzzerPassFlattenConditionalBranches(
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opt::IRContext* ir_context, TransformationContext* transformation_context,
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FuzzerContext* fuzzer_context,
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protobufs::TransformationSequence* transformations)
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: FuzzerPass(ir_context, transformation_context, fuzzer_context,
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transformations) {}
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FuzzerPassFlattenConditionalBranches::~FuzzerPassFlattenConditionalBranches() =
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default;
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void FuzzerPassFlattenConditionalBranches::Apply() {
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for (auto& function : *GetIRContext()->module()) {
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// Get all the selection headers that we want to flatten. We need to collect
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// all of them first, because, since we are changing the structure of the
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// module, it's not safe to modify them while iterating.
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std::vector<opt::BasicBlock*> selection_headers;
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for (auto& block : function) {
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// Randomly decide whether to consider this block.
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if (!GetFuzzerContext()->ChoosePercentage(
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GetFuzzerContext()->GetChanceOfFlatteningConditionalBranch())) {
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continue;
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}
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// Only consider this block if it is the header of a conditional, with a
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// non-irrelevant condition.
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if (block.GetMergeInst() &&
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block.GetMergeInst()->opcode() == SpvOpSelectionMerge &&
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block.terminator()->opcode() == SpvOpBranchConditional &&
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!GetTransformationContext()->GetFactManager()->IdIsIrrelevant(
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block.terminator()->GetSingleWordInOperand(0))) {
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selection_headers.emplace_back(&block);
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}
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}
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// Sort the headers so that those that are more deeply nested are considered
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// first, possibly enabling outer conditionals to be flattened.
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std::sort(selection_headers.begin(), selection_headers.end(),
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ComparatorDeepBlocksFirst(GetIRContext()));
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// Apply the transformation to the headers which can be flattened.
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for (auto header : selection_headers) {
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// Make a set to keep track of the instructions that need fresh ids.
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std::set<opt::Instruction*> instructions_that_need_ids;
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// Do not consider this header if the conditional cannot be flattened.
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if (!TransformationFlattenConditionalBranch::
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GetProblematicInstructionsIfConditionalCanBeFlattened(
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GetIRContext(), header, *GetTransformationContext(),
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&instructions_that_need_ids)) {
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continue;
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}
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uint32_t convergence_block_id =
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TransformationFlattenConditionalBranch::FindConvergenceBlock(
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GetIRContext(), *header);
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// If the SPIR-V version is restricted so that OpSelect can only work on
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// scalar, pointer and vector types then we cannot apply this
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// transformation to a header whose convergence block features OpPhi
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// instructions on different types, as we cannot convert such instructions
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// to OpSelect instructions.
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if (TransformationFlattenConditionalBranch::
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OpSelectArgumentsAreRestricted(GetIRContext())) {
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if (!GetIRContext()
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->cfg()
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->block(convergence_block_id)
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->WhileEachPhiInst(
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[this](opt::Instruction* phi_instruction) -> bool {
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switch (GetIRContext()
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->get_def_use_mgr()
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->GetDef(phi_instruction->type_id())
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->opcode()) {
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case SpvOpTypeBool:
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case SpvOpTypeInt:
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case SpvOpTypeFloat:
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case SpvOpTypePointer:
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case SpvOpTypeVector:
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return true;
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default:
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return false;
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}
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})) {
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// An OpPhi is performed on a type not supported by OpSelect; we
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// cannot flatten this selection.
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continue;
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}
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}
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// If the construct's convergence block features OpPhi instructions with
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// vector result types then we may be *forced*, by the SPIR-V version, to
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// turn these into component-wise OpSelect instructions, or we might wish
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// to do so anyway. The following booleans capture whether we will opt
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// to use a component-wise select even if we don't have to.
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bool use_component_wise_2d_select_even_if_optional =
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GetFuzzerContext()->ChooseEven();
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bool use_component_wise_3d_select_even_if_optional =
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GetFuzzerContext()->ChooseEven();
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bool use_component_wise_4d_select_even_if_optional =
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GetFuzzerContext()->ChooseEven();
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// If we do need to perform any component-wise selections, we will need a
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// fresh id for a boolean vector representing the selection's condition
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// repeated N times, where N is the vector dimension.
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uint32_t fresh_id_for_bvec2_selector = 0;
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uint32_t fresh_id_for_bvec3_selector = 0;
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uint32_t fresh_id_for_bvec4_selector = 0;
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GetIRContext()
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->cfg()
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->block(convergence_block_id)
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->ForEachPhiInst([this, &fresh_id_for_bvec2_selector,
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&fresh_id_for_bvec3_selector,
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&fresh_id_for_bvec4_selector,
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use_component_wise_2d_select_even_if_optional,
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use_component_wise_3d_select_even_if_optional,
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use_component_wise_4d_select_even_if_optional](
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opt::Instruction* phi_instruction) {
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opt::Instruction* type_instruction =
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GetIRContext()->get_def_use_mgr()->GetDef(
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phi_instruction->type_id());
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switch (type_instruction->opcode()) {
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case SpvOpTypeVector: {
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uint32_t dimension =
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type_instruction->GetSingleWordInOperand(1);
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switch (dimension) {
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case 2:
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PrepareForOpPhiOnVectors(
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dimension,
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use_component_wise_2d_select_even_if_optional,
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&fresh_id_for_bvec2_selector);
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break;
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case 3:
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PrepareForOpPhiOnVectors(
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dimension,
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use_component_wise_3d_select_even_if_optional,
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&fresh_id_for_bvec3_selector);
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break;
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case 4:
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PrepareForOpPhiOnVectors(
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dimension,
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use_component_wise_4d_select_even_if_optional,
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&fresh_id_for_bvec4_selector);
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break;
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default:
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assert(false && "Invalid vector dimension.");
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}
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break;
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}
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default:
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break;
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}
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});
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// Some instructions will require to be enclosed inside conditionals
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// because they have side effects (for example, loads and stores). Some of
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// this have no result id, so we require instruction descriptors to
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// identify them. Each of them is associated with the necessary ids for it
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// via a SideEffectWrapperInfo message.
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std::vector<protobufs::SideEffectWrapperInfo> wrappers_info;
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for (auto instruction : instructions_that_need_ids) {
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protobufs::SideEffectWrapperInfo wrapper_info;
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*wrapper_info.mutable_instruction() =
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MakeInstructionDescriptor(GetIRContext(), instruction);
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wrapper_info.set_merge_block_id(GetFuzzerContext()->GetFreshId());
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wrapper_info.set_execute_block_id(GetFuzzerContext()->GetFreshId());
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// If the instruction has a non-void result id, we need to define more
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// fresh ids and provide an id of the suitable type whose value can be
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// copied in order to create a placeholder id.
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if (TransformationFlattenConditionalBranch::InstructionNeedsPlaceholder(
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GetIRContext(), *instruction)) {
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wrapper_info.set_actual_result_id(GetFuzzerContext()->GetFreshId());
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wrapper_info.set_alternative_block_id(
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GetFuzzerContext()->GetFreshId());
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wrapper_info.set_placeholder_result_id(
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GetFuzzerContext()->GetFreshId());
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// The id will be a zero constant if the type allows it, and an
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// OpUndef otherwise. We want to avoid using OpUndef, if possible, to
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// avoid undefined behaviour in the module as much as possible.
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if (fuzzerutil::CanCreateConstant(GetIRContext(),
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instruction->type_id())) {
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wrapper_info.set_value_to_copy_id(
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FindOrCreateZeroConstant(instruction->type_id(), true));
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} else {
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wrapper_info.set_value_to_copy_id(
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FindOrCreateGlobalUndef(instruction->type_id()));
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}
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}
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wrappers_info.push_back(std::move(wrapper_info));
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}
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// Apply the transformation, evenly choosing whether to lay out the true
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// branch or the false branch first.
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ApplyTransformation(TransformationFlattenConditionalBranch(
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header->id(), GetFuzzerContext()->ChooseEven(),
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fresh_id_for_bvec2_selector, fresh_id_for_bvec3_selector,
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fresh_id_for_bvec4_selector, wrappers_info));
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}
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}
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}
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void FuzzerPassFlattenConditionalBranches::PrepareForOpPhiOnVectors(
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uint32_t vector_dimension, bool use_vector_select_if_optional,
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uint32_t* fresh_id_for_bvec_selector) {
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if (*fresh_id_for_bvec_selector != 0) {
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// We already have a fresh id for a component-wise OpSelect of this
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// dimension
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return;
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}
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if (TransformationFlattenConditionalBranch::OpSelectArgumentsAreRestricted(
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GetIRContext()) ||
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use_vector_select_if_optional) {
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// We either have to, or have chosen to, perform a component-wise select, so
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// we ensure that the right boolean vector type is available, and grab a
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// fresh id.
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FindOrCreateVectorType(FindOrCreateBoolType(), vector_dimension);
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*fresh_id_for_bvec_selector = GetFuzzerContext()->GetFreshId();
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}
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}
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} // namespace fuzz
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} // namespace spvtools
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