SPIRV-Tools/source/opt/loop_dependence_helpers.cpp

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// Copyright (c) 2018 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/opt/loop_dependence.h"
#include <ostream>
#include <set>
#include <string>
#include <unordered_set>
#include <utility>
#include <vector>
#include "source/opt/basic_block.h"
#include "source/opt/instruction.h"
#include "source/opt/scalar_analysis.h"
#include "source/opt/scalar_analysis_nodes.h"
namespace spvtools {
namespace opt {
bool LoopDependenceAnalysis::IsZIV(
const std::pair<SENode*, SENode*>& subscript_pair) {
return CountInductionVariables(subscript_pair.first, subscript_pair.second) ==
0;
}
bool LoopDependenceAnalysis::IsSIV(
const std::pair<SENode*, SENode*>& subscript_pair) {
return CountInductionVariables(subscript_pair.first, subscript_pair.second) ==
1;
}
bool LoopDependenceAnalysis::IsMIV(
const std::pair<SENode*, SENode*>& subscript_pair) {
return CountInductionVariables(subscript_pair.first, subscript_pair.second) >
1;
}
SENode* LoopDependenceAnalysis::GetLowerBound(const Loop* loop) {
Instruction* cond_inst = loop->GetConditionInst();
if (!cond_inst) {
return nullptr;
}
Instruction* lower_inst = GetOperandDefinition(cond_inst, 0);
switch (cond_inst->opcode()) {
case SpvOpULessThan:
case SpvOpSLessThan:
case SpvOpULessThanEqual:
case SpvOpSLessThanEqual:
case SpvOpUGreaterThan:
case SpvOpSGreaterThan:
case SpvOpUGreaterThanEqual:
case SpvOpSGreaterThanEqual: {
// If we have a phi we are looking at the induction variable. We look
// through the phi to the initial value of the phi upon entering the loop.
if (lower_inst->opcode() == SpvOpPhi) {
lower_inst = GetOperandDefinition(lower_inst, 0);
// We don't handle looking through multiple phis.
if (lower_inst->opcode() == SpvOpPhi) {
return nullptr;
}
}
return scalar_evolution_.SimplifyExpression(
scalar_evolution_.AnalyzeInstruction(lower_inst));
}
default:
return nullptr;
}
}
SENode* LoopDependenceAnalysis::GetUpperBound(const Loop* loop) {
Instruction* cond_inst = loop->GetConditionInst();
if (!cond_inst) {
return nullptr;
}
Instruction* upper_inst = GetOperandDefinition(cond_inst, 1);
switch (cond_inst->opcode()) {
case SpvOpULessThan:
case SpvOpSLessThan: {
// When we have a < condition we must subtract 1 from the analyzed upper
// instruction.
SENode* upper_bound = scalar_evolution_.SimplifyExpression(
scalar_evolution_.CreateSubtraction(
scalar_evolution_.AnalyzeInstruction(upper_inst),
scalar_evolution_.CreateConstant(1)));
return upper_bound;
}
case SpvOpUGreaterThan:
case SpvOpSGreaterThan: {
// When we have a > condition we must add 1 to the analyzed upper
// instruction.
SENode* upper_bound =
scalar_evolution_.SimplifyExpression(scalar_evolution_.CreateAddNode(
scalar_evolution_.AnalyzeInstruction(upper_inst),
scalar_evolution_.CreateConstant(1)));
return upper_bound;
}
case SpvOpULessThanEqual:
case SpvOpSLessThanEqual:
case SpvOpUGreaterThanEqual:
case SpvOpSGreaterThanEqual: {
// We don't need to modify the results of analyzing when we have <= or >=.
SENode* upper_bound = scalar_evolution_.SimplifyExpression(
scalar_evolution_.AnalyzeInstruction(upper_inst));
return upper_bound;
}
default:
return nullptr;
}
}
bool LoopDependenceAnalysis::IsWithinBounds(int64_t value, int64_t bound_one,
int64_t bound_two) {
if (bound_one < bound_two) {
// If |bound_one| is the lower bound.
return (value >= bound_one && value <= bound_two);
} else if (bound_one > bound_two) {
// If |bound_two| is the lower bound.
return (value >= bound_two && value <= bound_one);
} else {
// Both bounds have the same value.
return value == bound_one;
}
}
bool LoopDependenceAnalysis::IsProvablyOutsideOfLoopBounds(
const Loop* loop, SENode* distance, SENode* coefficient) {
// We test to see if we can reduce the coefficient to an integral constant.
SEConstantNode* coefficient_constant = coefficient->AsSEConstantNode();
if (!coefficient_constant) {
PrintDebug(
"IsProvablyOutsideOfLoopBounds could not reduce coefficient to a "
"SEConstantNode so must exit.");
return false;
}
SENode* lower_bound = GetLowerBound(loop);
SENode* upper_bound = GetUpperBound(loop);
if (!lower_bound || !upper_bound) {
PrintDebug(
"IsProvablyOutsideOfLoopBounds could not get both the lower and upper "
"bounds so must exit.");
return false;
}
// If the coefficient is positive we calculate bounds as upper - lower
// If the coefficient is negative we calculate bounds as lower - upper
SENode* bounds = nullptr;
if (coefficient_constant->FoldToSingleValue() >= 0) {
PrintDebug(
"IsProvablyOutsideOfLoopBounds found coefficient >= 0.\n"
"Using bounds as upper - lower.");
bounds = scalar_evolution_.SimplifyExpression(
scalar_evolution_.CreateSubtraction(upper_bound, lower_bound));
} else {
PrintDebug(
"IsProvablyOutsideOfLoopBounds found coefficient < 0.\n"
"Using bounds as lower - upper.");
bounds = scalar_evolution_.SimplifyExpression(
scalar_evolution_.CreateSubtraction(lower_bound, upper_bound));
}
// We can attempt to deal with symbolic cases by subtracting |distance| and
// the bound nodes. If we can subtract, simplify and produce a SEConstantNode
// we can produce some information.
SEConstantNode* distance_minus_bounds =
scalar_evolution_
.SimplifyExpression(
scalar_evolution_.CreateSubtraction(distance, bounds))
->AsSEConstantNode();
if (distance_minus_bounds) {
PrintDebug(
"IsProvablyOutsideOfLoopBounds found distance - bounds as a "
"SEConstantNode with value " +
ToString(distance_minus_bounds->FoldToSingleValue()));
// If distance - bounds > 0 we prove the distance is outwith the loop
// bounds.
if (distance_minus_bounds->FoldToSingleValue() > 0) {
PrintDebug(
"IsProvablyOutsideOfLoopBounds found distance escaped the loop "
"bounds.");
return true;
}
}
return false;
}
const Loop* LoopDependenceAnalysis::GetLoopForSubscriptPair(
const std::pair<SENode*, SENode*>& subscript_pair) {
// Collect all the SERecurrentNodes.
std::vector<SERecurrentNode*> source_nodes =
std::get<0>(subscript_pair)->CollectRecurrentNodes();
std::vector<SERecurrentNode*> destination_nodes =
std::get<1>(subscript_pair)->CollectRecurrentNodes();
// Collect all the loops stored by the SERecurrentNodes.
std::unordered_set<const Loop*> loops{};
for (auto source_nodes_it = source_nodes.begin();
source_nodes_it != source_nodes.end(); ++source_nodes_it) {
loops.insert((*source_nodes_it)->GetLoop());
}
for (auto destination_nodes_it = destination_nodes.begin();
destination_nodes_it != destination_nodes.end();
++destination_nodes_it) {
loops.insert((*destination_nodes_it)->GetLoop());
}
// If we didn't find 1 loop |subscript_pair| is a subscript over multiple or 0
// loops. We don't handle this so return nullptr.
if (loops.size() != 1) {
PrintDebug("GetLoopForSubscriptPair found loops.size() != 1.");
return nullptr;
}
return *loops.begin();
}
DistanceEntry* LoopDependenceAnalysis::GetDistanceEntryForLoop(
const Loop* loop, DistanceVector* distance_vector) {
if (!loop) {
return nullptr;
}
DistanceEntry* distance_entry = nullptr;
for (size_t loop_index = 0; loop_index < loops_.size(); ++loop_index) {
if (loop == loops_[loop_index]) {
distance_entry = &(distance_vector->GetEntries()[loop_index]);
break;
}
}
return distance_entry;
}
DistanceEntry* LoopDependenceAnalysis::GetDistanceEntryForSubscriptPair(
const std::pair<SENode*, SENode*>& subscript_pair,
DistanceVector* distance_vector) {
const Loop* loop = GetLoopForSubscriptPair(subscript_pair);
return GetDistanceEntryForLoop(loop, distance_vector);
}
SENode* LoopDependenceAnalysis::GetTripCount(const Loop* loop) {
BasicBlock* condition_block = loop->FindConditionBlock();
if (!condition_block) {
return nullptr;
}
Instruction* induction_instr = loop->FindConditionVariable(condition_block);
if (!induction_instr) {
return nullptr;
}
Instruction* cond_instr = loop->GetConditionInst();
if (!cond_instr) {
return nullptr;
}
size_t iteration_count = 0;
// We have to check the instruction type here. If the condition instruction
// isn't a supported type we can't calculate the trip count.
if (loop->IsSupportedCondition(cond_instr->opcode())) {
if (loop->FindNumberOfIterations(induction_instr, &*condition_block->tail(),
&iteration_count)) {
return scalar_evolution_.CreateConstant(
static_cast<int64_t>(iteration_count));
}
}
return nullptr;
}
SENode* LoopDependenceAnalysis::GetFirstTripInductionNode(const Loop* loop) {
BasicBlock* condition_block = loop->FindConditionBlock();
if (!condition_block) {
return nullptr;
}
Instruction* induction_instr = loop->FindConditionVariable(condition_block);
if (!induction_instr) {
return nullptr;
}
int64_t induction_initial_value = 0;
if (!loop->GetInductionInitValue(induction_instr, &induction_initial_value)) {
return nullptr;
}
SENode* induction_init_SENode = scalar_evolution_.SimplifyExpression(
scalar_evolution_.CreateConstant(induction_initial_value));
return induction_init_SENode;
}
SENode* LoopDependenceAnalysis::GetFinalTripInductionNode(
const Loop* loop, SENode* induction_coefficient) {
SENode* first_trip_induction_node = GetFirstTripInductionNode(loop);
if (!first_trip_induction_node) {
return nullptr;
}
// Get trip_count as GetTripCount - 1
// This is because the induction variable is not stepped on the first
// iteration of the loop
SENode* trip_count =
scalar_evolution_.SimplifyExpression(scalar_evolution_.CreateSubtraction(
GetTripCount(loop), scalar_evolution_.CreateConstant(1)));
// Return first_trip_induction_node + trip_count * induction_coefficient
return scalar_evolution_.SimplifyExpression(scalar_evolution_.CreateAddNode(
first_trip_induction_node,
scalar_evolution_.CreateMultiplyNode(trip_count, induction_coefficient)));
}
std::set<const Loop*> LoopDependenceAnalysis::CollectLoops(
const std::vector<SERecurrentNode*>& recurrent_nodes) {
// We don't handle loops with more than one induction variable. Therefore we
// can identify the number of induction variables by collecting all of the
// loops the collected recurrent nodes belong to.
std::set<const Loop*> loops{};
for (auto recurrent_nodes_it = recurrent_nodes.begin();
recurrent_nodes_it != recurrent_nodes.end(); ++recurrent_nodes_it) {
loops.insert((*recurrent_nodes_it)->GetLoop());
}
return loops;
}
int64_t LoopDependenceAnalysis::CountInductionVariables(SENode* node) {
if (!node) {
return -1;
}
std::vector<SERecurrentNode*> recurrent_nodes = node->CollectRecurrentNodes();
// We don't handle loops with more than one induction variable. Therefore we
// can identify the number of induction variables by collecting all of the
// loops the collected recurrent nodes belong to.
std::set<const Loop*> loops = CollectLoops(recurrent_nodes);
return static_cast<int64_t>(loops.size());
}
std::set<const Loop*> LoopDependenceAnalysis::CollectLoops(
SENode* source, SENode* destination) {
if (!source || !destination) {
return std::set<const Loop*>{};
}
std::vector<SERecurrentNode*> source_nodes = source->CollectRecurrentNodes();
std::vector<SERecurrentNode*> destination_nodes =
destination->CollectRecurrentNodes();
std::set<const Loop*> loops = CollectLoops(source_nodes);
std::set<const Loop*> destination_loops = CollectLoops(destination_nodes);
loops.insert(std::begin(destination_loops), std::end(destination_loops));
return loops;
}
int64_t LoopDependenceAnalysis::CountInductionVariables(SENode* source,
SENode* destination) {
if (!source || !destination) {
return -1;
}
std::set<const Loop*> loops = CollectLoops(source, destination);
return static_cast<int64_t>(loops.size());
}
Instruction* LoopDependenceAnalysis::GetOperandDefinition(
const Instruction* instruction, int id) {
return context_->get_def_use_mgr()->GetDef(
instruction->GetSingleWordInOperand(id));
}
std::vector<Instruction*> LoopDependenceAnalysis::GetSubscripts(
const Instruction* instruction) {
Instruction* access_chain = GetOperandDefinition(instruction, 0);
std::vector<Instruction*> subscripts;
for (auto i = 1u; i < access_chain->NumInOperandWords(); ++i) {
subscripts.push_back(GetOperandDefinition(access_chain, i));
}
return subscripts;
}
SENode* LoopDependenceAnalysis::GetConstantTerm(const Loop* loop,
SERecurrentNode* induction) {
SENode* offset = induction->GetOffset();
SENode* lower_bound = GetLowerBound(loop);
if (!offset || !lower_bound) {
return nullptr;
}
SENode* constant_term = scalar_evolution_.SimplifyExpression(
scalar_evolution_.CreateSubtraction(offset, lower_bound));
return constant_term;
}
bool LoopDependenceAnalysis::CheckSupportedLoops(
std::vector<const Loop*> loops) {
for (auto loop : loops) {
if (!IsSupportedLoop(loop)) {
return false;
}
}
return true;
}
void LoopDependenceAnalysis::MarkUnsusedDistanceEntriesAsIrrelevant(
const Instruction* source, const Instruction* destination,
DistanceVector* distance_vector) {
std::vector<Instruction*> source_subscripts = GetSubscripts(source);
std::vector<Instruction*> destination_subscripts = GetSubscripts(destination);
std::set<const Loop*> used_loops{};
for (Instruction* source_inst : source_subscripts) {
SENode* source_node = scalar_evolution_.SimplifyExpression(
scalar_evolution_.AnalyzeInstruction(source_inst));
std::vector<SERecurrentNode*> recurrent_nodes =
source_node->CollectRecurrentNodes();
for (SERecurrentNode* recurrent_node : recurrent_nodes) {
used_loops.insert(recurrent_node->GetLoop());
}
}
for (Instruction* destination_inst : destination_subscripts) {
SENode* destination_node = scalar_evolution_.SimplifyExpression(
scalar_evolution_.AnalyzeInstruction(destination_inst));
std::vector<SERecurrentNode*> recurrent_nodes =
destination_node->CollectRecurrentNodes();
for (SERecurrentNode* recurrent_node : recurrent_nodes) {
used_loops.insert(recurrent_node->GetLoop());
}
}
for (size_t i = 0; i < loops_.size(); ++i) {
if (used_loops.find(loops_[i]) == used_loops.end()) {
distance_vector->GetEntries()[i].dependence_information =
DistanceEntry::DependenceInformation::IRRELEVANT;
}
}
}
bool LoopDependenceAnalysis::IsSupportedLoop(const Loop* loop) {
std::vector<Instruction*> inductions{};
loop->GetInductionVariables(inductions);
if (inductions.size() != 1) {
return false;
}
Instruction* induction = inductions[0];
SENode* induction_node = scalar_evolution_.SimplifyExpression(
scalar_evolution_.AnalyzeInstruction(induction));
if (!induction_node->AsSERecurrentNode()) {
return false;
}
SENode* induction_step =
induction_node->AsSERecurrentNode()->GetCoefficient();
if (!induction_step->AsSEConstantNode()) {
return false;
}
if (!(induction_step->AsSEConstantNode()->FoldToSingleValue() == 1 ||
induction_step->AsSEConstantNode()->FoldToSingleValue() == -1)) {
return false;
}
return true;
}
void LoopDependenceAnalysis::PrintDebug(std::string debug_msg) {
if (debug_stream_) {
(*debug_stream_) << debug_msg << "\n";
}
}
bool Constraint::operator==(const Constraint& other) const {
// A distance of |d| is equivalent to a line |x - y = -d|
if ((GetType() == ConstraintType::Distance &&
other.GetType() == ConstraintType::Line) ||
(GetType() == ConstraintType::Line &&
other.GetType() == ConstraintType::Distance)) {
auto is_distance = AsDependenceLine() != nullptr;
auto as_distance =
is_distance ? AsDependenceDistance() : other.AsDependenceDistance();
auto distance = as_distance->GetDistance();
auto line = other.AsDependenceLine();
auto scalar_evolution = distance->GetParentAnalysis();
auto neg_distance = scalar_evolution->SimplifyExpression(
scalar_evolution->CreateNegation(distance));
return *scalar_evolution->CreateConstant(1) == *line->GetA() &&
*scalar_evolution->CreateConstant(-1) == *line->GetB() &&
*neg_distance == *line->GetC();
}
if (GetType() != other.GetType()) {
return false;
}
if (AsDependenceDistance()) {
return *AsDependenceDistance()->GetDistance() ==
*other.AsDependenceDistance()->GetDistance();
}
if (AsDependenceLine()) {
auto this_line = AsDependenceLine();
auto other_line = other.AsDependenceLine();
return *this_line->GetA() == *other_line->GetA() &&
*this_line->GetB() == *other_line->GetB() &&
*this_line->GetC() == *other_line->GetC();
}
if (AsDependencePoint()) {
auto this_point = AsDependencePoint();
auto other_point = other.AsDependencePoint();
return *this_point->GetSource() == *other_point->GetSource() &&
*this_point->GetDestination() == *other_point->GetDestination();
}
return true;
}
bool Constraint::operator!=(const Constraint& other) const {
return !(*this == other);
}
} // namespace opt
} // namespace spvtools