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// Copyright (c) 2016 Google Inc.
// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include "source/opt/fold_spec_constant_op_and_composite_pass.h"
#include <algorithm>
#include <tuple>
#include "source/opt/constants.h"
#include "source/util/make_unique.h"
namespace spvtools {
namespace opt {
Pass::Status FoldSpecConstantOpAndCompositePass::Process() {
bool modified = false;
analysis::ConstantManager* const_mgr = context()->get_constant_mgr();
// Traverse through all the constant defining instructions. For Normal
// Constants whose values are determined and do not depend on OpUndef
// instructions, records their values in two internal maps: id_to_const_val_
// and const_val_to_id_ so that we can use them to infer the value of Spec
// Constants later.
// For Spec Constants defined with OpSpecConstantComposite instructions, if
// all of their components are Normal Constants, they will be turned into
// Normal Constants too. For Spec Constants defined with OpSpecConstantOp
// instructions, we check if they only depends on Normal Constants and fold
// them when possible. The two maps for Normal Constants: id_to_const_val_
// and const_val_to_id_ will be updated along the traversal so that the new
// Normal Constants generated from folding can be used to fold following Spec
// Constants.
// This algorithm depends on the SSA property of SPIR-V when
// defining constants. The dependent constants must be defined before the
// dependee constants. So a dependent Spec Constant must be defined and
// will be processed before its dependee Spec Constant. When we encounter
// the dependee Spec Constants, all its dependent constants must have been
// processed and all its dependent Spec Constants should have been folded if
// possible.
Module::inst_iterator next_inst = context()->types_values_begin();
for (Module::inst_iterator inst_iter = next_inst;
// Need to re-evaluate the end iterator since we may modify the list of
// instructions in this section of the module as the process goes.
inst_iter != context()->types_values_end(); inst_iter = next_inst) {
Instruction* inst = &*inst_iter;
// Collect constant values of normal constants and process the
// OpSpecConstantOp and OpSpecConstantComposite instructions if possible.
// The constant values will be stored in analysis::Constant instances.
// OpConstantSampler instruction is not collected here because it cannot be
// used in OpSpecConstant{Composite|Op} instructions.
// TODO(qining): If the constant or its type has decoration, we may need
// to skip it.
if (const_mgr->GetType(inst) &&
switch (spv::Op opcode = inst->opcode()) {
// Records the values of Normal Constants.
case spv::Op::OpConstantTrue:
case spv::Op::OpConstantFalse:
case spv::Op::OpConstant:
case spv::Op::OpConstantNull:
case spv::Op::OpConstantComposite:
case spv::Op::OpSpecConstantComposite: {
// A Constant instance will be created if the given instruction is a
// Normal Constant whose value(s) are fixed. Note that for a composite
// Spec Constant defined with OpSpecConstantComposite instruction, if
// all of its components are Normal Constants already, the Spec
// Constant will be turned in to a Normal Constant. In that case, a
// Constant instance should also be created successfully and recorded
// in the id_to_const_val_ and const_val_to_id_ mapps.
if (auto const_value = const_mgr->GetConstantFromInst(inst)) {
// Need to replace the OpSpecConstantComposite instruction with a
// corresponding OpConstantComposite instruction.
if (opcode == spv::Op::OpSpecConstantComposite) {
modified = true;
const_mgr->MapConstantToInst(const_value, inst);
// For a Spec Constants defined with OpSpecConstantOp instruction, check
// if it only depends on Normal Constants. If so, the Spec Constant will
// be folded. The original Spec Constant defining instruction will be
// replaced by Normal Constant defining instructions, and the new Normal
// Constants will be added to id_to_const_val_ and const_val_to_id_ so
// that we can use the new Normal Constants when folding following Spec
// Constants.
case spv::Op::OpSpecConstantOp:
modified |= ProcessOpSpecConstantOp(&inst_iter);
return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
bool FoldSpecConstantOpAndCompositePass::ProcessOpSpecConstantOp(
Module::inst_iterator* pos) {
Instruction* inst = &**pos;
Instruction* folded_inst = nullptr;
assert(inst->GetInOperand(0).type ==
"The first in-operand of OpSpecConstantOp instruction must be of "
folded_inst = FoldWithInstructionFolder(pos);
if (!folded_inst) {
folded_inst = DoComponentWiseOperation(pos);
if (!folded_inst) return false;
// Replace the original constant with the new folded constant, kill the
// original constant.
uint32_t new_id = folded_inst->result_id();
uint32_t old_id = inst->result_id();
context()->ReplaceAllUsesWith(old_id, new_id);
return true;
Instruction* FoldSpecConstantOpAndCompositePass::FoldWithInstructionFolder(
Module::inst_iterator* inst_iter_ptr) {
analysis::ConstantManager* const_mgr = context()->get_constant_mgr();
// If one of operands to the instruction is not a
// constant, then we cannot fold this spec constant.
for (uint32_t i = 1; i < (*inst_iter_ptr)->NumInOperands(); i++) {
const Operand& operand = (*inst_iter_ptr)->GetInOperand(i);
if (operand.type != SPV_OPERAND_TYPE_ID &&
uint32_t id = operand.words[0];
if (const_mgr->FindDeclaredConstant(id) == nullptr) {
return nullptr;
// All of the operands are constant. Construct a regular version of the
// instruction and pass it to the instruction folder.
std::unique_ptr<Instruction> inst((*inst_iter_ptr)->Clone(context()));
// We want the current instruction to be replaced by an |OpConstant*|
// instruction in the same position. We need to keep track of which constants
// the instruction folder creates, so we can move them into the correct place.
auto last_type_value_iter = (context()->types_values_end());
Instruction* last_type_value = &*last_type_value_iter;
auto identity_map = [](uint32_t id) { return id; };
Instruction* new_const_inst =
inst.get(), identity_map);
// new_const_inst == null indicates we cannot fold this spec constant
if (!new_const_inst) return nullptr;
// Get the instruction before |pos| to insert after. |pos| cannot be the
// first instruction in the list because its type has to come first.
Instruction* insert_pos = (*inst_iter_ptr)->PreviousNode();
assert(insert_pos != nullptr &&
"pos is the first instruction in the types and values.");
bool need_to_clone = true;
for (Instruction* i = last_type_value->NextNode(); i != nullptr;
i = last_type_value->NextNode()) {
if (i == new_const_inst) {
need_to_clone = false;
insert_pos = insert_pos->NextNode();
if (need_to_clone) {
new_const_inst = new_const_inst->Clone(context());
return new_const_inst;
namespace {
// A helper function to check the type for component wise operations. Returns
// true if the type:
// 1) is bool type;
// 2) is 32-bit int type;
// 3) is vector of bool type;
// 4) is vector of 32-bit integer type.
// Otherwise returns false.
bool IsValidTypeForComponentWiseOperation(const analysis::Type* type) {
if (type->AsBool()) {
return true;
} else if (auto* it = type->AsInteger()) {
if (it->width() == 32) return true;
} else if (auto* vt = type->AsVector()) {
if (vt->element_type()->AsBool()) {
return true;
} else if (auto* vit = vt->element_type()->AsInteger()) {
if (vit->width() == 32) return true;
return false;
// Encodes the integer |value| of in a word vector format appropriate for
// representing this value as a operands for a constant definition. Performs
// zero-extension/sign-extension/truncation when needed, based on the signess of
// the given target type.
// Note: type |type| argument must be either Integer or Bool.
utils::SmallVector<uint32_t, 2> EncodeIntegerAsWords(const analysis::Type& type,
uint32_t value) {
const uint32_t all_ones = ~0;
uint32_t bit_width = 0;
uint32_t pad_value = 0;
bool result_type_signed = false;
if (auto* int_ty = type.AsInteger()) {
bit_width = int_ty->width();
result_type_signed = int_ty->IsSigned();
if (result_type_signed && static_cast<int32_t>(value) < 0) {
pad_value = all_ones;
} else if (type.AsBool()) {
bit_width = 1;
} else {
assert(false && "type must be Integer or Bool");
assert(bit_width > 0);
uint32_t first_word = value;
const uint32_t bits_per_word = 32;
// Truncate first_word if the |type| has width less than uint32.
if (bit_width < bits_per_word) {
const uint32_t num_high_bits_to_mask = bits_per_word - bit_width;
const bool is_negative_after_truncation =
result_type_signed &&
utils::IsBitAtPositionSet(first_word, bit_width - 1);
if (is_negative_after_truncation) {
// Truncate and sign-extend |first_word|. No padding words will be
// added and |pad_value| can be left as-is.
first_word = utils::SetHighBits(first_word, num_high_bits_to_mask);
} else {
first_word = utils::ClearHighBits(first_word, num_high_bits_to_mask);
utils::SmallVector<uint32_t, 2> words = {first_word};
for (uint32_t current_bit = bits_per_word; current_bit < bit_width;
current_bit += bits_per_word) {
return words;
} // namespace
Instruction* FoldSpecConstantOpAndCompositePass::DoComponentWiseOperation(
Module::inst_iterator* pos) {
const Instruction* inst = &**pos;
analysis::ConstantManager* const_mgr = context()->get_constant_mgr();
const analysis::Type* result_type = const_mgr->GetType(inst);
spv::Op spec_opcode = static_cast<spv::Op>(inst->GetSingleWordInOperand(0));
// Check and collect operands.
std::vector<const analysis::Constant*> operands;
if (!std::all_of(
inst->cbegin(), inst->cend(), [&operands, this](const Operand& o) {
// skip the operands that is not an id.
if (o.type != spv_operand_type_t::SPV_OPERAND_TYPE_ID) return true;
uint32_t id = o.words.front();
if (auto c =
context()->get_constant_mgr()->FindDeclaredConstant(id)) {
if (IsValidTypeForComponentWiseOperation(c->type())) {
return true;
return false;
return nullptr;
if (result_type->AsInteger() || result_type->AsBool()) {
// Scalar operation
const uint32_t result_val =
context()->get_instruction_folder().FoldScalars(spec_opcode, operands);
auto result_const = const_mgr->GetConstant(
result_type, EncodeIntegerAsWords(*result_type, result_val));
return const_mgr->BuildInstructionAndAddToModule(result_const, pos);
} else if (result_type->AsVector()) {
// Vector operation
const analysis::Type* element_type =
uint32_t num_dims = result_type->AsVector()->element_count();
std::vector<uint32_t> result_vec =
context()->get_instruction_folder().FoldVectors(spec_opcode, num_dims,
std::vector<const analysis::Constant*> result_vector_components;
for (const uint32_t r : result_vec) {
if (auto rc = const_mgr->GetConstant(
element_type, EncodeIntegerAsWords(*element_type, r))) {
if (!const_mgr->BuildInstructionAndAddToModule(rc, pos)) {
assert(false &&
"Failed to build and insert constant declaring instruction "
"for the given vector component constant");
} else {
assert(false && "Failed to create constants with 32-bit word");
auto new_vec_const = MakeUnique<analysis::VectorConstant>(
result_type->AsVector(), result_vector_components);
auto reg_vec_const = const_mgr->RegisterConstant(std::move(new_vec_const));
return const_mgr->BuildInstructionAndAddToModule(reg_vec_const, pos);
} else {
// Cannot process invalid component wise operation. The result of component
// wise operation must be of integer or bool scalar or vector of
// integer/bool type.
return nullptr;
} // namespace opt
} // namespace spvtools