source/fuzz/fuzzer_util.cpp - external/github.com/KhronosGroup/SPIRV-Tools - Git at Google

 // Copyright (c) 2019 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/fuzzer_util.h"

 #include "source/opt/build_module.h"

 namespace spvtools {
 namespace fuzz {

 namespace fuzzerutil {

 bool IsFreshId(opt::IRContext* context, uint32_t id) {
   return !context->get_def_use_mgr()->GetDef(id);
 }

 void UpdateModuleIdBound(opt::IRContext* context, uint32_t id) {
   // TODO(https://github.com/KhronosGroup/SPIRV-Tools/issues/2541) consider the
   //  case where the maximum id bound is reached.
   context->module()->SetIdBound(
       std::max(context->module()->id_bound(), id + 1));
 }

 opt::BasicBlock* MaybeFindBlock(opt::IRContext* context,
                                 uint32_t maybe_block_id) {
   auto inst = context->get_def_use_mgr()->GetDef(maybe_block_id);
   if (inst == nullptr) {
     // No instruction defining this id was found.
     return nullptr;
   }
   if (inst->opcode() != SpvOpLabel) {
     // The instruction defining the id is not a label, so it cannot be a block
     // id.
     return nullptr;
   }
   return context->cfg()->block(maybe_block_id);
 }

 bool PhiIdsOkForNewEdge(
     opt::IRContext* context, opt::BasicBlock* bb_from, opt::BasicBlock* bb_to,
     const google::protobuf::RepeatedField<google::protobuf::uint32>& phi_ids) {
   if (bb_from->IsSuccessor(bb_to)) {
     // There is already an edge from |from_block| to |to_block|, so there is
     // no need to extend OpPhi instructions.  Do not allow phi ids to be
     // present. This might turn out to be too strict; perhaps it would be OK
     // just to ignore the ids in this case.
     return phi_ids.empty();
   }
   // The edge would add a previously non-existent edge from |from_block| to
   // |to_block|, so we go through the given phi ids and check that they exactly
   // match the OpPhi instructions in |to_block|.
   uint32_t phi_index = 0;
   // An explicit loop, rather than applying a lambda to each OpPhi in |bb_to|,
   // makes sense here because we need to increment |phi_index| for each OpPhi
   // instruction.
   for (auto& inst : *bb_to) {
     if (inst.opcode() != SpvOpPhi) {
       // The OpPhi instructions all occur at the start of the block; if we find
       // a non-OpPhi then we have seen them all.
       break;
     }
     if (phi_index == static_cast<uint32_t>(phi_ids.size())) {
       // Not enough phi ids have been provided to account for the OpPhi
       // instructions.
       return false;
     }
     // Look for an instruction defining the next phi id.
     opt::Instruction* phi_extension =
         context->get_def_use_mgr()->GetDef(phi_ids[phi_index]);
     if (!phi_extension) {
       // The id given to extend this OpPhi does not exist.
       return false;
     }
     if (phi_extension->type_id() != inst.type_id()) {
       // The instruction given to extend this OpPhi either does not have a type
       // or its type does not match that of the OpPhi.
       return false;
     }

     if (context->get_instr_block(phi_extension)) {
       // The instruction defining the phi id has an associated block (i.e., it
       // is not a global value).  Check whether its definition dominates the
       // exit of |from_block|.
       auto dominator_analysis =
           context->GetDominatorAnalysis(bb_from->GetParent());
       if (!dominator_analysis->Dominates(phi_extension,
                                          bb_from->terminator())) {
         // The given id is no good as its definition does not dominate the exit
         // of |from_block|
         return false;
       }
     }
     phi_index++;
   }
   // We allow some of the ids provided for extending OpPhi instructions to be
   // unused.  Their presence does no harm, and requiring a perfect match may
   // make transformations less likely to cleanly apply.
   return true;
 }

 uint32_t MaybeGetBoolConstantId(opt::IRContext* context, bool value) {
   opt::analysis::Bool bool_type;
   auto registered_bool_type =
       context->get_type_mgr()->GetRegisteredType(&bool_type);
   if (!registered_bool_type) {
     return 0;
   }
   opt::analysis::BoolConstant bool_constant(registered_bool_type->AsBool(),
                                             value);
   return context->get_constant_mgr()->FindDeclaredConstant(
       &bool_constant, context->get_type_mgr()->GetId(&bool_type));
 }

 void AddUnreachableEdgeAndUpdateOpPhis(
     opt::IRContext* context, opt::BasicBlock* bb_from, opt::BasicBlock* bb_to,
     bool condition_value,
     const google::protobuf::RepeatedField<google::protobuf::uint32>& phi_ids) {
   assert(PhiIdsOkForNewEdge(context, bb_from, bb_to, phi_ids) &&
          "Precondition on phi_ids is not satisfied");
   assert(bb_from->terminator()->opcode() == SpvOpBranch &&
          "Precondition on terminator of bb_from is not satisfied");

   // Get the id of the boolean constant to be used as the condition.
   uint32_t bool_id = MaybeGetBoolConstantId(context, condition_value);
   assert(
       bool_id &&
       "Precondition that condition value must be available is not satisfied");

   const bool from_to_edge_already_exists = bb_from->IsSuccessor(bb_to);
   auto successor = bb_from->terminator()->GetSingleWordInOperand(0);

   // Add the dead branch, by turning OpBranch into OpBranchConditional, and
   // ordering the targets depending on whether the given boolean corresponds to
   // true or false.
   bb_from->terminator()->SetOpcode(SpvOpBranchConditional);
   bb_from->terminator()->SetInOperands(
       {{SPV_OPERAND_TYPE_ID, {bool_id}},
        {SPV_OPERAND_TYPE_ID, {condition_value ? successor : bb_to->id()}},
        {SPV_OPERAND_TYPE_ID, {condition_value ? bb_to->id() : successor}}});

   // Update OpPhi instructions in the target block if this branch adds a
   // previously non-existent edge from source to target.
   if (!from_to_edge_already_exists) {
     uint32_t phi_index = 0;
     for (auto& inst : *bb_to) {
       if (inst.opcode() != SpvOpPhi) {
         break;
       }
       assert(phi_index < static_cast<uint32_t>(phi_ids.size()) &&
              "There should be at least one phi id per OpPhi instruction.");
       inst.AddOperand({SPV_OPERAND_TYPE_ID, {phi_ids[phi_index]}});
       inst.AddOperand({SPV_OPERAND_TYPE_ID, {bb_from->id()}});
       phi_index++;
     }
   }
 }

 bool BlockIsInLoopContinueConstruct(opt::IRContext* context, uint32_t block_id,
                                     uint32_t maybe_loop_header_id) {
   // We deem a block to be part of a loop's continue construct if the loop's
   // continue target dominates the block.
   auto containing_construct_block = context->cfg()->block(maybe_loop_header_id);
   if (containing_construct_block->IsLoopHeader()) {
     auto continue_target = containing_construct_block->ContinueBlockId();
     if (context->GetDominatorAnalysis(containing_construct_block->GetParent())
             ->Dominates(continue_target, block_id)) {
       return true;
     }
   }
   return false;
 }

 opt::BasicBlock::iterator GetIteratorForInstruction(
     opt::BasicBlock* block, const opt::Instruction* inst) {
   for (auto inst_it = block->begin(); inst_it != block->end(); ++inst_it) {
     if (inst == &*inst_it) {
       return inst_it;
     }
   }
   return block->end();
 }

 bool BlockIsReachableInItsFunction(opt::IRContext* context,
                                    opt::BasicBlock* bb) {
   auto enclosing_function = bb->GetParent();
   return context->GetDominatorAnalysis(enclosing_function)
       ->Dominates(enclosing_function->entry().get(), bb);
 }

 bool CanInsertOpcodeBeforeInstruction(
     SpvOp opcode, const opt::BasicBlock::iterator& instruction_in_block) {
   if (instruction_in_block->PreviousNode() &&
       (instruction_in_block->PreviousNode()->opcode() == SpvOpLoopMerge ||
        instruction_in_block->PreviousNode()->opcode() == SpvOpSelectionMerge)) {
     // We cannot insert directly after a merge instruction.
     return false;
   }
   if (opcode != SpvOpVariable &&
       instruction_in_block->opcode() == SpvOpVariable) {
     // We cannot insert a non-OpVariable instruction directly before a
     // variable; variables in a function must be contiguous in the entry block.
     return false;
   }
   // We cannot insert a non-OpPhi instruction directly before an OpPhi, because
   // OpPhi instructions need to be contiguous at the start of a block.
   return opcode == SpvOpPhi || instruction_in_block->opcode() != SpvOpPhi;
 }

 bool CanMakeSynonymOf(opt::IRContext* ir_context, opt::Instruction* inst) {
   if (!inst->HasResultId()) {
     // We can only make a synonym of an instruction that generates an id.
     return false;
   }
   if (!inst->type_id()) {
     // We can only make a synonym of an instruction that has a type.
     return false;
   }
   auto type_inst = ir_context->get_def_use_mgr()->GetDef(inst->type_id());
   if (type_inst->opcode() == SpvOpTypePointer) {
     switch (inst->opcode()) {
       case SpvOpConstantNull:
       case SpvOpUndef:
         // We disallow making synonyms of null or undefined pointers.  This is
         // to provide the property that if the original shader exhibited no bad
         // pointer accesses, the transformed shader will not either.
         return false;
       default:
         break;
     }
   }

   // We do not make synonyms of objects that have decorations: if the synonym is
   // not decorated analogously, using the original object vs. its synonymous
   // form may not be equivalent.
   return ir_context->get_decoration_mgr()
       ->GetDecorationsFor(inst->result_id(), true)
       .empty();
 }

 bool IsCompositeType(const opt::analysis::Type* type) {
   return type && (type->AsArray() || type->AsMatrix() || type->AsStruct() ||
                   type->AsVector());
 }

 std::vector<uint32_t> RepeatedFieldToVector(
     const google::protobuf::RepeatedField<uint32_t>& repeated_field) {
   std::vector<uint32_t> result;
   for (auto i : repeated_field) {
     result.push_back(i);
   }
   return result;
 }

 uint32_t WalkOneCompositeTypeIndex(opt::IRContext* context,
                                    uint32_t base_object_type_id,
                                    uint32_t index) {
   auto should_be_composite_type =
       context->get_def_use_mgr()->GetDef(base_object_type_id);
   assert(should_be_composite_type && "The type should exist.");
   switch (should_be_composite_type->opcode()) {
     case SpvOpTypeArray: {
       auto array_length = GetArraySize(*should_be_composite_type, context);
       if (array_length == 0 || index >= array_length) {
         return 0;
       }
       return should_be_composite_type->GetSingleWordInOperand(0);
     }
     case SpvOpTypeMatrix:
     case SpvOpTypeVector: {
       auto count = should_be_composite_type->GetSingleWordInOperand(1);
       if (index >= count) {
         return 0;
       }
       return should_be_composite_type->GetSingleWordInOperand(0);
     }
     case SpvOpTypeStruct: {
       if (index >= GetNumberOfStructMembers(*should_be_composite_type)) {
         return 0;
       }
       return should_be_composite_type->GetSingleWordInOperand(index);
     }
     default:
       return 0;
   }
 }

 uint32_t WalkCompositeTypeIndices(
     opt::IRContext* context, uint32_t base_object_type_id,
     const google::protobuf::RepeatedField<google::protobuf::uint32>& indices) {
   uint32_t sub_object_type_id = base_object_type_id;
   for (auto index : indices) {
     sub_object_type_id =
         WalkOneCompositeTypeIndex(context, sub_object_type_id, index);
     if (!sub_object_type_id) {
       return 0;
     }
   }
   return sub_object_type_id;
 }

 uint32_t GetNumberOfStructMembers(
     const opt::Instruction& struct_type_instruction) {
   assert(struct_type_instruction.opcode() == SpvOpTypeStruct &&
          "An OpTypeStruct instruction is required here.");
   return struct_type_instruction.NumInOperands();
 }

 uint32_t GetArraySize(const opt::Instruction& array_type_instruction,
                       opt::IRContext* context) {
   auto array_length_constant =
       context->get_constant_mgr()
           ->GetConstantFromInst(context->get_def_use_mgr()->GetDef(
               array_type_instruction.GetSingleWordInOperand(1)))
           ->AsIntConstant();
   if (array_length_constant->words().size() != 1) {
     return 0;
   }
   return array_length_constant->GetU32();
 }

 bool IsValid(opt::IRContext* context) {
   std::vector<uint32_t> binary;
   context->module()->ToBinary(&binary, false);
   SpirvTools tools(context->grammar().target_env());
   return tools.Validate(binary);
 }

 std::unique_ptr<opt::IRContext> CloneIRContext(opt::IRContext* context) {
   std::vector<uint32_t> binary;
   context->module()->ToBinary(&binary, false);
   return BuildModule(context->grammar().target_env(), nullptr, binary.data(),
                      binary.size());
 }

 bool IsNonFunctionTypeId(opt::IRContext* ir_context, uint32_t id) {
   auto type = ir_context->get_type_mgr()->GetType(id);
   return type && !type->AsFunction();
 }

 bool IsMergeOrContinue(opt::IRContext* ir_context, uint32_t block_id) {
   bool result = false;
   ir_context->get_def_use_mgr()->WhileEachUse(
       block_id,
       [&result](const opt::Instruction* use_instruction,
                 uint32_t /*unused*/) -> bool {
         switch (use_instruction->opcode()) {
           case SpvOpLoopMerge:
           case SpvOpSelectionMerge:
             result = true;
             return false;
           default:
             return true;
         }
       });
   return result;
 }

 uint32_t FindFunctionType(opt::IRContext* ir_context,
                           const std::vector<uint32_t>& type_ids) {
   // Look through the existing types for a match.
   for (auto& type_or_value : ir_context->types_values()) {
     if (type_or_value.opcode() != SpvOpTypeFunction) {
       // We are only interested in function types.
       continue;
     }
     if (type_or_value.NumInOperands() != type_ids.size()) {
       // Not a match: different numbers of arguments.
       continue;
     }
     // Check whether the return type and argument types match.
     bool input_operands_match = true;
     for (uint32_t i = 0; i < type_or_value.NumInOperands(); i++) {
       if (type_ids[i] != type_or_value.GetSingleWordInOperand(i)) {
         input_operands_match = false;
         break;
       }
     }
     if (input_operands_match) {
       // Everything matches.
       return type_or_value.result_id();
     }
   }
   // No match was found.
   return 0;
 }

 opt::Function* FindFunction(opt::IRContext* ir_context, uint32_t function_id) {
   for (auto& function : *ir_context->module()) {
     if (function.result_id() == function_id) {
       return &function;
     }
   }
   return nullptr;
 }

 bool IdIsAvailableAtUse(opt::IRContext* context,
                         opt::Instruction* use_instruction,
                         uint32_t use_input_operand_index, uint32_t id) {
   auto defining_instruction = context->get_def_use_mgr()->GetDef(id);
   auto enclosing_function =
       context->get_instr_block(use_instruction)->GetParent();
   // If the id a function parameter, it needs to be associated with the
   // function containing the use.
   if (defining_instruction->opcode() == SpvOpFunctionParameter) {
     return InstructionIsFunctionParameter(defining_instruction,
                                           enclosing_function);
   }
   if (!context->get_instr_block(id)) {
     // The id must be at global scope.
     return true;
   }
   if (defining_instruction == use_instruction) {
     // It is not OK for a definition to use itself.
     return false;
   }
   auto dominator_analysis = context->GetDominatorAnalysis(enclosing_function);
   if (use_instruction->opcode() == SpvOpPhi) {
     // In the case where the use is an operand to OpPhi, it is actually the
     // *parent* block associated with the operand that must be dominated by
     // the synonym.
     auto parent_block =
         use_instruction->GetSingleWordInOperand(use_input_operand_index + 1);
     return dominator_analysis->Dominates(
         context->get_instr_block(defining_instruction)->id(), parent_block);
   }
   return dominator_analysis->Dominates(defining_instruction, use_instruction);
 }

 bool IdIsAvailableBeforeInstruction(opt::IRContext* context,
                                     opt::Instruction* instruction,
                                     uint32_t id) {
   auto defining_instruction = context->get_def_use_mgr()->GetDef(id);
   auto enclosing_function = context->get_instr_block(instruction)->GetParent();
   // If the id a function parameter, it needs to be associated with the
   // function containing the instruction.
   if (defining_instruction->opcode() == SpvOpFunctionParameter) {
     return InstructionIsFunctionParameter(defining_instruction,
                                           enclosing_function);
   }
   if (!context->get_instr_block(id)) {
     // The id is at global scope.
     return true;
   }
   if (defining_instruction == instruction) {
     // The instruction is not available right before its own definition.
     return false;
   }
   return context->GetDominatorAnalysis(enclosing_function)
       ->Dominates(defining_instruction, instruction);
 }

 bool InstructionIsFunctionParameter(opt::Instruction* instruction,
                                     opt::Function* function) {
   if (instruction->opcode() != SpvOpFunctionParameter) {
     return false;
   }
   bool found_parameter = false;
   function->ForEachParam(
       [instruction, &found_parameter](opt::Instruction* param) {
         if (param == instruction) {
           found_parameter = true;
         }
       });
   return found_parameter;
 }

 uint32_t GetTypeId(opt::IRContext* context, uint32_t result_id) {
   return context->get_def_use_mgr()->GetDef(result_id)->type_id();
 }

 uint32_t GetPointeeTypeIdFromPointerType(opt::Instruction* pointer_type_inst) {
   assert(pointer_type_inst && pointer_type_inst->opcode() == SpvOpTypePointer &&
          "Precondition: |pointer_type_inst| must be OpTypePointer.");
   return pointer_type_inst->GetSingleWordInOperand(1);
 }

 uint32_t GetPointeeTypeIdFromPointerType(opt::IRContext* context,
                                          uint32_t pointer_type_id) {
   return GetPointeeTypeIdFromPointerType(
       context->get_def_use_mgr()->GetDef(pointer_type_id));
 }

 SpvStorageClass GetStorageClassFromPointerType(
     opt::Instruction* pointer_type_inst) {
   assert(pointer_type_inst && pointer_type_inst->opcode() == SpvOpTypePointer &&
          "Precondition: |pointer_type_inst| must be OpTypePointer.");
   return static_cast<SpvStorageClass>(
       pointer_type_inst->GetSingleWordInOperand(0));
 }

 SpvStorageClass GetStorageClassFromPointerType(opt::IRContext* context,
                                                uint32_t pointer_type_id) {
   return GetStorageClassFromPointerType(
       context->get_def_use_mgr()->GetDef(pointer_type_id));
 }

 uint32_t MaybeGetPointerType(opt::IRContext* context, uint32_t pointee_type_id,
                              SpvStorageClass storage_class) {
   for (auto& inst : context->types_values()) {
     switch (inst.opcode()) {
       case SpvOpTypePointer:
         if (inst.GetSingleWordInOperand(0) == storage_class &&
             inst.GetSingleWordInOperand(1) == pointee_type_id) {
           return inst.result_id();
         }
         break;
       default:
         break;
     }
   }
   return 0;
 }

 }  // namespace fuzzerutil

 }  // namespace fuzz
 }  // namespace spvtools
	// Copyright (c) 2019 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/fuzzer_util.h"

	#include "source/opt/build_module.h"

	namespace spvtools {
	namespace fuzz {

	namespace fuzzerutil {

	bool IsFreshId(opt::IRContext* context, uint32_t id) {
	return !context->get_def_use_mgr()->GetDef(id);
	}

	void UpdateModuleIdBound(opt::IRContext* context, uint32_t id) {
	// TODO(https://github.com/KhronosGroup/SPIRV-Tools/issues/2541) consider the
	// case where the maximum id bound is reached.
	context->module()->SetIdBound(
	std::max(context->module()->id_bound(), id + 1));
	}

	opt::BasicBlock* MaybeFindBlock(opt::IRContext* context,
	uint32_t maybe_block_id) {
	auto inst = context->get_def_use_mgr()->GetDef(maybe_block_id);
	if (inst == nullptr) {
	// No instruction defining this id was found.
	return nullptr;
	}
	if (inst->opcode() != SpvOpLabel) {
	// The instruction defining the id is not a label, so it cannot be a block
	// id.
	return nullptr;
	}
	return context->cfg()->block(maybe_block_id);
	}

	bool PhiIdsOkForNewEdge(
	opt::IRContext* context, opt::BasicBlock* bb_from, opt::BasicBlock* bb_to,
	const google::protobuf::RepeatedField<google::protobuf::uint32>& phi_ids) {
	if (bb_from->IsSuccessor(bb_to)) {
	// There is already an edge from \|from_block\| to \|to_block\|, so there is
	// no need to extend OpPhi instructions. Do not allow phi ids to be
	// present. This might turn out to be too strict; perhaps it would be OK
	// just to ignore the ids in this case.
	return phi_ids.empty();
	}
	// The edge would add a previously non-existent edge from \|from_block\| to
	// \|to_block\|, so we go through the given phi ids and check that they exactly
	// match the OpPhi instructions in \|to_block\|.
	uint32_t phi_index = 0;
	// An explicit loop, rather than applying a lambda to each OpPhi in \|bb_to\|,
	// makes sense here because we need to increment \|phi_index\| for each OpPhi
	// instruction.
	for (auto& inst : *bb_to) {
	if (inst.opcode() != SpvOpPhi) {
	// The OpPhi instructions all occur at the start of the block; if we find
	// a non-OpPhi then we have seen them all.
	break;
	}
	if (phi_index == static_cast<uint32_t>(phi_ids.size())) {
	// Not enough phi ids have been provided to account for the OpPhi
	// instructions.
	return false;
	}
	// Look for an instruction defining the next phi id.
	opt::Instruction* phi_extension =
	context->get_def_use_mgr()->GetDef(phi_ids[phi_index]);
	if (!phi_extension) {
	// The id given to extend this OpPhi does not exist.
	return false;
	}
	if (phi_extension->type_id() != inst.type_id()) {
	// The instruction given to extend this OpPhi either does not have a type
	// or its type does not match that of the OpPhi.
	return false;
	}

	if (context->get_instr_block(phi_extension)) {
	// The instruction defining the phi id has an associated block (i.e., it
	// is not a global value). Check whether its definition dominates the
	// exit of \|from_block\|.
	auto dominator_analysis =
	context->GetDominatorAnalysis(bb_from->GetParent());
	if (!dominator_analysis->Dominates(phi_extension,
	bb_from->terminator())) {
	// The given id is no good as its definition does not dominate the exit
	// of \|from_block\|
	return false;
	}
	}
	phi_index++;
	}
	// We allow some of the ids provided for extending OpPhi instructions to be
	// unused. Their presence does no harm, and requiring a perfect match may
	// make transformations less likely to cleanly apply.
	return true;
	}

	uint32_t MaybeGetBoolConstantId(opt::IRContext* context, bool value) {
	opt::analysis::Bool bool_type;
	auto registered_bool_type =
	context->get_type_mgr()->GetRegisteredType(&bool_type);
	if (!registered_bool_type) {
	return 0;
	}
	opt::analysis::BoolConstant bool_constant(registered_bool_type->AsBool(),
	value);
	return context->get_constant_mgr()->FindDeclaredConstant(
	&bool_constant, context->get_type_mgr()->GetId(&bool_type));
	}

	void AddUnreachableEdgeAndUpdateOpPhis(
	opt::IRContext* context, opt::BasicBlock* bb_from, opt::BasicBlock* bb_to,
	bool condition_value,
	const google::protobuf::RepeatedField<google::protobuf::uint32>& phi_ids) {
	assert(PhiIdsOkForNewEdge(context, bb_from, bb_to, phi_ids) &&
	"Precondition on phi_ids is not satisfied");
	assert(bb_from->terminator()->opcode() == SpvOpBranch &&
	"Precondition on terminator of bb_from is not satisfied");

	// Get the id of the boolean constant to be used as the condition.
	uint32_t bool_id = MaybeGetBoolConstantId(context, condition_value);
	assert(
	bool_id &&
	"Precondition that condition value must be available is not satisfied");

	const bool from_to_edge_already_exists = bb_from->IsSuccessor(bb_to);
	auto successor = bb_from->terminator()->GetSingleWordInOperand(0);

	// Add the dead branch, by turning OpBranch into OpBranchConditional, and
	// ordering the targets depending on whether the given boolean corresponds to
	// true or false.
	bb_from->terminator()->SetOpcode(SpvOpBranchConditional);
	bb_from->terminator()->SetInOperands(
	{{SPV_OPERAND_TYPE_ID, {bool_id}},
	{SPV_OPERAND_TYPE_ID, {condition_value ? successor : bb_to->id()}},
	{SPV_OPERAND_TYPE_ID, {condition_value ? bb_to->id() : successor}}});

	// Update OpPhi instructions in the target block if this branch adds a
	// previously non-existent edge from source to target.
	if (!from_to_edge_already_exists) {
	uint32_t phi_index = 0;
	for (auto& inst : *bb_to) {
	if (inst.opcode() != SpvOpPhi) {
	break;
	}
	assert(phi_index < static_cast<uint32_t>(phi_ids.size()) &&
	"There should be at least one phi id per OpPhi instruction.");
	inst.AddOperand({SPV_OPERAND_TYPE_ID, {phi_ids[phi_index]}});
	inst.AddOperand({SPV_OPERAND_TYPE_ID, {bb_from->id()}});
	phi_index++;
	}
	}
	}

	bool BlockIsInLoopContinueConstruct(opt::IRContext* context, uint32_t block_id,
	uint32_t maybe_loop_header_id) {
	// We deem a block to be part of a loop's continue construct if the loop's
	// continue target dominates the block.
	auto containing_construct_block = context->cfg()->block(maybe_loop_header_id);
	if (containing_construct_block->IsLoopHeader()) {
	auto continue_target = containing_construct_block->ContinueBlockId();
	if (context->GetDominatorAnalysis(containing_construct_block->GetParent())
	->Dominates(continue_target, block_id)) {
	return true;
	}
	}
	return false;
	}

	opt::BasicBlock::iterator GetIteratorForInstruction(
	opt::BasicBlock* block, const opt::Instruction* inst) {
	for (auto inst_it = block->begin(); inst_it != block->end(); ++inst_it) {
	if (inst == &*inst_it) {
	return inst_it;
	}
	}
	return block->end();
	}

	bool BlockIsReachableInItsFunction(opt::IRContext* context,
	opt::BasicBlock* bb) {
	auto enclosing_function = bb->GetParent();
	return context->GetDominatorAnalysis(enclosing_function)
	->Dominates(enclosing_function->entry().get(), bb);
	}

	bool CanInsertOpcodeBeforeInstruction(
	SpvOp opcode, const opt::BasicBlock::iterator& instruction_in_block) {
	if (instruction_in_block->PreviousNode() &&
	(instruction_in_block->PreviousNode()->opcode() == SpvOpLoopMerge \|\|
	instruction_in_block->PreviousNode()->opcode() == SpvOpSelectionMerge)) {
	// We cannot insert directly after a merge instruction.
	return false;
	}
	if (opcode != SpvOpVariable &&
	instruction_in_block->opcode() == SpvOpVariable) {
	// We cannot insert a non-OpVariable instruction directly before a
	// variable; variables in a function must be contiguous in the entry block.
	return false;
	}
	// We cannot insert a non-OpPhi instruction directly before an OpPhi, because
	// OpPhi instructions need to be contiguous at the start of a block.
	return opcode == SpvOpPhi \|\| instruction_in_block->opcode() != SpvOpPhi;
	}

	bool CanMakeSynonymOf(opt::IRContext* ir_context, opt::Instruction* inst) {
	if (!inst->HasResultId()) {
	// We can only make a synonym of an instruction that generates an id.
	return false;
	}
	if (!inst->type_id()) {
	// We can only make a synonym of an instruction that has a type.
	return false;
	}
	auto type_inst = ir_context->get_def_use_mgr()->GetDef(inst->type_id());
	if (type_inst->opcode() == SpvOpTypePointer) {
	switch (inst->opcode()) {
	case SpvOpConstantNull:
	case SpvOpUndef:
	// We disallow making synonyms of null or undefined pointers. This is
	// to provide the property that if the original shader exhibited no bad
	// pointer accesses, the transformed shader will not either.
	return false;
	default:
	break;
	}
	}

	// We do not make synonyms of objects that have decorations: if the synonym is
	// not decorated analogously, using the original object vs. its synonymous
	// form may not be equivalent.
	return ir_context->get_decoration_mgr()
	->GetDecorationsFor(inst->result_id(), true)
	.empty();
	}

	bool IsCompositeType(const opt::analysis::Type* type) {
	return type && (type->AsArray() \|\| type->AsMatrix() \|\| type->AsStruct() \|\|
	type->AsVector());
	}

	std::vector<uint32_t> RepeatedFieldToVector(
	const google::protobuf::RepeatedField<uint32_t>& repeated_field) {
	std::vector<uint32_t> result;
	for (auto i : repeated_field) {
	result.push_back(i);
	}
	return result;
	}

	uint32_t WalkOneCompositeTypeIndex(opt::IRContext* context,
	uint32_t base_object_type_id,
	uint32_t index) {
	auto should_be_composite_type =
	context->get_def_use_mgr()->GetDef(base_object_type_id);
	assert(should_be_composite_type && "The type should exist.");
	switch (should_be_composite_type->opcode()) {
	case SpvOpTypeArray: {
	auto array_length = GetArraySize(*should_be_composite_type, context);
	if (array_length == 0 \|\| index >= array_length) {
	return 0;
	}
	return should_be_composite_type->GetSingleWordInOperand(0);
	}
	case SpvOpTypeMatrix:
	case SpvOpTypeVector: {
	auto count = should_be_composite_type->GetSingleWordInOperand(1);
	if (index >= count) {
	return 0;
	}
	return should_be_composite_type->GetSingleWordInOperand(0);
	}
	case SpvOpTypeStruct: {
	if (index >= GetNumberOfStructMembers(*should_be_composite_type)) {
	return 0;
	}
	return should_be_composite_type->GetSingleWordInOperand(index);
	}
	default:
	return 0;
	}
	}

	uint32_t WalkCompositeTypeIndices(
	opt::IRContext* context, uint32_t base_object_type_id,
	const google::protobuf::RepeatedField<google::protobuf::uint32>& indices) {
	uint32_t sub_object_type_id = base_object_type_id;
	for (auto index : indices) {
	sub_object_type_id =
	WalkOneCompositeTypeIndex(context, sub_object_type_id, index);
	if (!sub_object_type_id) {
	return 0;
	}
	}
	return sub_object_type_id;
	}

	uint32_t GetNumberOfStructMembers(
	const opt::Instruction& struct_type_instruction) {
	assert(struct_type_instruction.opcode() == SpvOpTypeStruct &&
	"An OpTypeStruct instruction is required here.");
	return struct_type_instruction.NumInOperands();
	}

	uint32_t GetArraySize(const opt::Instruction& array_type_instruction,
	opt::IRContext* context) {
	auto array_length_constant =
	context->get_constant_mgr()
	->GetConstantFromInst(context->get_def_use_mgr()->GetDef(
	array_type_instruction.GetSingleWordInOperand(1)))
	->AsIntConstant();
	if (array_length_constant->words().size() != 1) {
	return 0;
	}
	return array_length_constant->GetU32();
	}

	bool IsValid(opt::IRContext* context) {
	std::vector<uint32_t> binary;
	context->module()->ToBinary(&binary, false);
	SpirvTools tools(context->grammar().target_env());
	return tools.Validate(binary);
	}

	std::unique_ptr<opt::IRContext> CloneIRContext(opt::IRContext* context) {
	std::vector<uint32_t> binary;
	context->module()->ToBinary(&binary, false);
	return BuildModule(context->grammar().target_env(), nullptr, binary.data(),
	binary.size());
	}

	bool IsNonFunctionTypeId(opt::IRContext* ir_context, uint32_t id) {
	auto type = ir_context->get_type_mgr()->GetType(id);
	return type && !type->AsFunction();
	}

	bool IsMergeOrContinue(opt::IRContext* ir_context, uint32_t block_id) {
	bool result = false;
	ir_context->get_def_use_mgr()->WhileEachUse(
	block_id,
	[&result](const opt::Instruction* use_instruction,
	uint32_t /unused/) -> bool {
	switch (use_instruction->opcode()) {
	case SpvOpLoopMerge:
	case SpvOpSelectionMerge:
	result = true;
	return false;
	default:
	return true;
	}
	});
	return result;
	}

	uint32_t FindFunctionType(opt::IRContext* ir_context,
	const std::vector<uint32_t>& type_ids) {
	// Look through the existing types for a match.
	for (auto& type_or_value : ir_context->types_values()) {
	if (type_or_value.opcode() != SpvOpTypeFunction) {
	// We are only interested in function types.
	continue;
	}
	if (type_or_value.NumInOperands() != type_ids.size()) {
	// Not a match: different numbers of arguments.
	continue;
	}
	// Check whether the return type and argument types match.
	bool input_operands_match = true;
	for (uint32_t i = 0; i < type_or_value.NumInOperands(); i++) {
	if (type_ids[i] != type_or_value.GetSingleWordInOperand(i)) {
	input_operands_match = false;
	break;
	}
	}
	if (input_operands_match) {
	// Everything matches.
	return type_or_value.result_id();
	}
	}
	// No match was found.
	return 0;
	}

	opt::Function* FindFunction(opt::IRContext* ir_context, uint32_t function_id) {
	for (auto& function : *ir_context->module()) {
	if (function.result_id() == function_id) {
	return &function;
	}
	}
	return nullptr;
	}

	bool IdIsAvailableAtUse(opt::IRContext* context,
	opt::Instruction* use_instruction,
	uint32_t use_input_operand_index, uint32_t id) {
	auto defining_instruction = context->get_def_use_mgr()->GetDef(id);
	auto enclosing_function =
	context->get_instr_block(use_instruction)->GetParent();
	// If the id a function parameter, it needs to be associated with the
	// function containing the use.
	if (defining_instruction->opcode() == SpvOpFunctionParameter) {
	return InstructionIsFunctionParameter(defining_instruction,
	enclosing_function);
	}
	if (!context->get_instr_block(id)) {
	// The id must be at global scope.
	return true;
	}
	if (defining_instruction == use_instruction) {
	// It is not OK for a definition to use itself.
	return false;
	}
	auto dominator_analysis = context->GetDominatorAnalysis(enclosing_function);
	if (use_instruction->opcode() == SpvOpPhi) {
	// In the case where the use is an operand to OpPhi, it is actually the
	// parent block associated with the operand that must be dominated by
	// the synonym.
	auto parent_block =
	use_instruction->GetSingleWordInOperand(use_input_operand_index + 1);
	return dominator_analysis->Dominates(
	context->get_instr_block(defining_instruction)->id(), parent_block);
	}
	return dominator_analysis->Dominates(defining_instruction, use_instruction);
	}

	bool IdIsAvailableBeforeInstruction(opt::IRContext* context,
	opt::Instruction* instruction,
	uint32_t id) {
	auto defining_instruction = context->get_def_use_mgr()->GetDef(id);
	auto enclosing_function = context->get_instr_block(instruction)->GetParent();
	// If the id a function parameter, it needs to be associated with the
	// function containing the instruction.
	if (defining_instruction->opcode() == SpvOpFunctionParameter) {
	return InstructionIsFunctionParameter(defining_instruction,
	enclosing_function);
	}
	if (!context->get_instr_block(id)) {
	// The id is at global scope.
	return true;
	}
	if (defining_instruction == instruction) {
	// The instruction is not available right before its own definition.
	return false;
	}
	return context->GetDominatorAnalysis(enclosing_function)
	->Dominates(defining_instruction, instruction);
	}

	bool InstructionIsFunctionParameter(opt::Instruction* instruction,
	opt::Function* function) {
	if (instruction->opcode() != SpvOpFunctionParameter) {
	return false;
	}
	bool found_parameter = false;
	function->ForEachParam(
	[instruction, &found_parameter](opt::Instruction* param) {
	if (param == instruction) {
	found_parameter = true;
	}
	});
	return found_parameter;
	}

	uint32_t GetTypeId(opt::IRContext* context, uint32_t result_id) {
	return context->get_def_use_mgr()->GetDef(result_id)->type_id();
	}

	uint32_t GetPointeeTypeIdFromPointerType(opt::Instruction* pointer_type_inst) {
	assert(pointer_type_inst && pointer_type_inst->opcode() == SpvOpTypePointer &&
	"Precondition: \|pointer_type_inst\| must be OpTypePointer.");
	return pointer_type_inst->GetSingleWordInOperand(1);
	}

	uint32_t GetPointeeTypeIdFromPointerType(opt::IRContext* context,
	uint32_t pointer_type_id) {
	return GetPointeeTypeIdFromPointerType(
	context->get_def_use_mgr()->GetDef(pointer_type_id));
	}

	SpvStorageClass GetStorageClassFromPointerType(
	opt::Instruction* pointer_type_inst) {
	assert(pointer_type_inst && pointer_type_inst->opcode() == SpvOpTypePointer &&
	"Precondition: \|pointer_type_inst\| must be OpTypePointer.");
	return static_cast<SpvStorageClass>(
	pointer_type_inst->GetSingleWordInOperand(0));
	}

	SpvStorageClass GetStorageClassFromPointerType(opt::IRContext* context,
	uint32_t pointer_type_id) {
	return GetStorageClassFromPointerType(
	context->get_def_use_mgr()->GetDef(pointer_type_id));
	}

	uint32_t MaybeGetPointerType(opt::IRContext* context, uint32_t pointee_type_id,
	SpvStorageClass storage_class) {
	for (auto& inst : context->types_values()) {
	switch (inst.opcode()) {
	case SpvOpTypePointer:
	if (inst.GetSingleWordInOperand(0) == storage_class &&
	inst.GetSingleWordInOperand(1) == pointee_type_id) {
	return inst.result_id();
	}
	break;
	default:
	break;
	}
	}
	return 0;
	}

	} // namespace fuzzerutil

	} // namespace fuzz
	} // namespace spvtools