SPIRV-Tools/source/opt/strength_reduction_pass.cpp

195 lines
6.3 KiB
C++
Raw Normal View History

// Copyright (c) 2017 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
//
// 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/opt/strength_reduction_pass.h"
#include <cstring>
#include <memory>
#include <utility>
#include <vector>
#include "source/opt/def_use_manager.h"
#include "source/opt/ir_context.h"
#include "source/opt/log.h"
#include "source/opt/reflect.h"
namespace spvtools {
namespace opt {
namespace {
// Count the number of trailing zeros in the binary representation of
// |constVal|.
uint32_t CountTrailingZeros(uint32_t constVal) {
// Faster if we use the hardware count trailing zeros instruction.
// If not available, we could create a table.
uint32_t shiftAmount = 0;
while ((constVal & 1) == 0) {
++shiftAmount;
constVal = (constVal >> 1);
}
return shiftAmount;
}
// Return true if |val| is a power of 2.
bool IsPowerOf2(uint32_t val) {
// The idea is that the & will clear out the least
// significant 1 bit. If it is a power of 2, then
// there is exactly 1 bit set, and the value becomes 0.
if (val == 0) return false;
return ((val - 1) & val) == 0;
}
} // namespace
Pass::Status StrengthReductionPass::Process() {
// Initialize the member variables on a per module basis.
bool modified = false;
int32_type_id_ = 0;
uint32_type_id_ = 0;
std::memset(constant_ids_, 0, sizeof(constant_ids_));
FindIntTypesAndConstants();
modified = ScanFunctions();
return (modified ? Status::SuccessWithChange : Status::SuccessWithoutChange);
}
bool StrengthReductionPass::ReplaceMultiplyByPowerOf2(
BasicBlock::iterator* inst) {
assert((*inst)->opcode() == spv::Op::OpIMul &&
"Only works for multiplication of integers.");
bool modified = false;
// Currently only works on 32-bit integers.
if ((*inst)->type_id() != int32_type_id_ &&
(*inst)->type_id() != uint32_type_id_) {
return modified;
}
// Check the operands for a constant that is a power of 2.
for (int i = 0; i < 2; i++) {
uint32_t opId = (*inst)->GetSingleWordInOperand(i);
Instruction* opInst = get_def_use_mgr()->GetDef(opId);
if (opInst->opcode() == spv::Op::OpConstant) {
// We found a constant operand.
uint32_t constVal = opInst->GetSingleWordOperand(2);
if (IsPowerOf2(constVal)) {
modified = true;
uint32_t shiftAmount = CountTrailingZeros(constVal);
uint32_t shiftConstResultId = GetConstantId(shiftAmount);
// Create the new instruction.
uint32_t newResultId = TakeNextId();
std::vector<Operand> newOperands;
newOperands.push_back((*inst)->GetInOperand(1 - i));
Operand shiftOperand(spv_operand_type_t::SPV_OPERAND_TYPE_ID,
{shiftConstResultId});
newOperands.push_back(shiftOperand);
std::unique_ptr<Instruction> newInstruction(
new Instruction(context(), spv::Op::OpShiftLeftLogical,
(*inst)->type_id(), newResultId, newOperands));
// Insert the new instruction and update the data structures.
(*inst) = (*inst).InsertBefore(std::move(newInstruction));
get_def_use_mgr()->AnalyzeInstDefUse(&*(*inst));
++(*inst);
context()->ReplaceAllUsesWith((*inst)->result_id(), newResultId);
// Remove the old instruction.
Instruction* inst_to_delete = &*(*inst);
--(*inst);
context()->KillInst(inst_to_delete);
// We do not want to replace the instruction twice if both operands
// are constants that are a power of 2. So we break here.
break;
}
}
}
return modified;
}
void StrengthReductionPass::FindIntTypesAndConstants() {
analysis::Integer int32(32, true);
int32_type_id_ = context()->get_type_mgr()->GetId(&int32);
analysis::Integer uint32(32, false);
uint32_type_id_ = context()->get_type_mgr()->GetId(&uint32);
for (auto iter = get_module()->types_values_begin();
iter != get_module()->types_values_end(); ++iter) {
switch (iter->opcode()) {
case spv::Op::OpConstant:
if (iter->type_id() == uint32_type_id_) {
uint32_t value = iter->GetSingleWordOperand(2);
if (value <= 32) constant_ids_[value] = iter->result_id();
}
break;
default:
break;
}
}
}
uint32_t StrengthReductionPass::GetConstantId(uint32_t val) {
assert(val <= 32 &&
"This function does not handle constants larger than 32.");
if (constant_ids_[val] == 0) {
if (uint32_type_id_ == 0) {
analysis::Integer uint(32, false);
uint32_type_id_ = context()->get_type_mgr()->GetTypeInstruction(&uint);
}
// Construct the constant.
uint32_t resultId = TakeNextId();
Operand constant(spv_operand_type_t::SPV_OPERAND_TYPE_LITERAL_INTEGER,
{val});
std::unique_ptr<Instruction> newConstant(new Instruction(
context(), spv::Op::OpConstant, uint32_type_id_, resultId, {constant}));
get_module()->AddGlobalValue(std::move(newConstant));
Adding new def -> use mapping container Replaced representation of uses * Changed uses from unordered_map<uint32_t, UseList> to set<pairInstruction*, Instruction*>> * Replaced GetUses with ForEachUser and ForEachUse functions * updated passes to use new functions * partially updated tests * lots of cleanup still todo Adding an unique id to Instruction generated by IRContext Each instruction is given an unique id that can be used for ordering purposes. The ids are generated via the IRContext. Major changes: * Instructions now contain a uint32_t for unique id and a cached context pointer * Most constructors have been modified to take a context as input * unfortunately I cannot remove the default and copy constructors, but developers should avoid these * Added accessors to parents of basic block and function * Removed the copy constructors for BasicBlock and Function and replaced them with Clone functions * Reworked BuildModule to return an IRContext owning the built module * Since all instructions require a context, the context now becomes the basic unit for IR * Added a constructor to context to create an owned module internally * Replaced uses of Instruction's copy constructor with Clone whereever I found them * Reworked the linker functionality to perform clones into a different context instead of moves * Updated many tests to be consistent with the above changes * Still need to add new tests to cover added functionality * Added comparison operators to Instruction Adding tests for Instruction, IRContext and IR loading Fixed some header comments for BuildModule Fixes to get tests passing again * Reordered two linker steps to avoid use/def problems * Fixed def/use manager uses in merge return pass * Added early return for GetAnnotations * Changed uses of Instruction::ToNop in passes to IRContext::KillInst Simplifying the uses for some contexts in passes
2017-11-14 19:11:50 +00:00
// Notify the DefUseManager about this constant.
auto constantIter = --get_module()->types_values_end();
get_def_use_mgr()->AnalyzeInstDef(&*constantIter);
// Store the result id for next time.
constant_ids_[val] = resultId;
}
return constant_ids_[val];
}
bool StrengthReductionPass::ScanFunctions() {
// I did not use |ForEachInst| in the module because the function that acts on
// the instruction gets a pointer to the instruction. We cannot use that to
// insert a new instruction. I want an iterator.
bool modified = false;
for (auto& func : *get_module()) {
for (auto& bb : func) {
for (auto inst = bb.begin(); inst != bb.end(); ++inst) {
switch (inst->opcode()) {
case spv::Op::OpIMul:
if (ReplaceMultiplyByPowerOf2(&inst)) modified = true;
break;
default:
break;
}
}
}
}
return modified;
}
} // namespace opt
} // namespace spvtools