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// Copyright (c) 2020 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/fuzz/transformation_replace_branch_from_dead_block_with_exit.h"
#include "source/fuzz/fuzzer_util.h"
namespace spvtools {
namespace fuzz {
TransformationReplaceBranchFromDeadBlockWithExit::
TransformationReplaceBranchFromDeadBlockWithExit(
protobufs::TransformationReplaceBranchFromDeadBlockWithExit message)
: message_(std::move(message)) {}
TransformationReplaceBranchFromDeadBlockWithExit::
TransformationReplaceBranchFromDeadBlockWithExit(uint32_t block_id,
spv::Op opcode,
uint32_t return_value_id) {
message_.set_block_id(block_id);
message_.set_opcode(uint32_t(opcode));
message_.set_return_value_id(return_value_id);
}
bool TransformationReplaceBranchFromDeadBlockWithExit::IsApplicable(
opt::IRContext* ir_context,
const TransformationContext& transformation_context) const {
// The block whose terminator is to be changed must exist.
auto block = ir_context->get_instr_block(message_.block_id());
if (!block) {
return false;
}
if (!BlockIsSuitable(ir_context, transformation_context, *block)) {
return false;
}
auto function_return_type_id = block->GetParent()->type_id();
switch (spv::Op(message_.opcode())) {
case spv::Op::OpKill:
for (auto& entry_point : ir_context->module()->entry_points()) {
if (spv::ExecutionModel(entry_point.GetSingleWordInOperand(0)) !=
spv::ExecutionModel::Fragment) {
// OpKill is only allowed in a fragment shader. This is a
// conservative check: if the module contains a non-fragment entry
// point then adding an OpKill might lead to OpKill being used in a
// non-fragment shader.
return false;
}
}
break;
case spv::Op::OpReturn:
if (ir_context->get_def_use_mgr()
->GetDef(function_return_type_id)
->opcode() != spv::Op::OpTypeVoid) {
// OpReturn is only allowed in a function with void return type.
return false;
}
break;
case spv::Op::OpReturnValue: {
// If the terminator is to be changed to OpReturnValue, with
// |message_.return_value_id| being the value that will be returned, then
// |message_.return_value_id| must have a compatible type and be available
// at the block terminator.
auto return_value =
ir_context->get_def_use_mgr()->GetDef(message_.return_value_id());
if (!return_value || return_value->type_id() != function_return_type_id) {
return false;
}
if (!fuzzerutil::IdIsAvailableBeforeInstruction(
ir_context, block->terminator(), message_.return_value_id())) {
return false;
}
break;
}
default:
assert(spv::Op(message_.opcode()) == spv::Op::OpUnreachable &&
"Invalid early exit opcode.");
break;
}
return true;
}
void TransformationReplaceBranchFromDeadBlockWithExit::Apply(
opt::IRContext* ir_context, TransformationContext* /*unused*/) const {
// If the successor block has OpPhi instructions then arguments related to
// |message_.block_id| need to be removed from these instruction.
auto block = ir_context->get_instr_block(message_.block_id());
assert(block->terminator()->opcode() == spv::Op::OpBranch &&
"Precondition: the block must end with OpBranch.");
auto successor = ir_context->get_instr_block(
block->terminator()->GetSingleWordInOperand(0));
successor->ForEachPhiInst([block](opt::Instruction* phi_inst) {
opt::Instruction::OperandList new_phi_in_operands;
for (uint32_t i = 0; i < phi_inst->NumInOperands(); i += 2) {
if (phi_inst->GetSingleWordInOperand(i + 1) == block->id()) {
continue;
}
new_phi_in_operands.emplace_back(phi_inst->GetInOperand(i));
new_phi_in_operands.emplace_back(phi_inst->GetInOperand(i + 1));
}
assert(new_phi_in_operands.size() == phi_inst->NumInOperands() - 2);
phi_inst->SetInOperands(std::move(new_phi_in_operands));
});
// Rewrite the terminator of |message_.block_id|.
opt::Instruction::OperandList new_terminator_in_operands;
if (spv::Op(message_.opcode()) == spv::Op::OpReturnValue) {
new_terminator_in_operands.push_back(
{SPV_OPERAND_TYPE_ID, {message_.return_value_id()}});
}
auto terminator = block->terminator();
terminator->SetOpcode(static_cast<spv::Op>(message_.opcode()));
terminator->SetInOperands(std::move(new_terminator_in_operands));
ir_context->InvalidateAnalysesExceptFor(opt::IRContext::kAnalysisNone);
}
std::unordered_set<uint32_t>
TransformationReplaceBranchFromDeadBlockWithExit::GetFreshIds() const {
return std::unordered_set<uint32_t>();
}
protobufs::Transformation
TransformationReplaceBranchFromDeadBlockWithExit::ToMessage() const {
protobufs::Transformation result;
*result.mutable_replace_branch_from_dead_block_with_exit() = message_;
return result;
}
bool TransformationReplaceBranchFromDeadBlockWithExit::BlockIsSuitable(
opt::IRContext* ir_context,
const TransformationContext& transformation_context,
const opt::BasicBlock& block) {
// The block must be dead.
if (!transformation_context.GetFactManager()->BlockIsDead(block.id())) {
return false;
}
// The block's terminator must be OpBranch.
if (block.terminator()->opcode() != spv::Op::OpBranch) {
return false;
}
if (ir_context->GetStructuredCFGAnalysis()->IsInContinueConstruct(
block.id())) {
// Early exits from continue constructs are not allowed as they would break
// the SPIR-V structured control flow rules.
return false;
}
// We only allow changing OpBranch to an early terminator if the target of the
// OpBranch has at least one other predecessor.
auto successor = ir_context->get_instr_block(
block.terminator()->GetSingleWordInOperand(0));
if (ir_context->cfg()->preds(successor->id()).size() < 2) {
return false;
}
// Make sure that domination rules are satisfied when we remove the branch
// from the |block| to its |successor|.
return fuzzerutil::NewTerminatorPreservesDominationRules(
ir_context, block.id(), {ir_context, spv::Op::OpUnreachable});
}
} // namespace fuzz
} // namespace spvtools
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