Revision a3cac6513d39c01592fa92e77aee1f5033e0209a authored by Dan Palermo on 14 June 2021, 18:29:20 UTC, committed by Dan Palermo on 14 June 2021, 18:29:20 UTC
1 parent 08cc265
SplitTuples.cpp
#include "SplitTuples.h"
#include "Bounds.h"
#include "CSE.h"
#include "ExprUsesVar.h"
#include "Function.h"
#include "IRMutator.h"
#include "IROperator.h"
#include "Simplify.h"
#include "Substitute.h"
namespace Halide {
namespace Internal {
using std::map;
using std::pair;
using std::set;
using std::string;
using std::vector;
namespace {
// Collect all value indices of internal halide calls.
class FindCallValueIndices : public IRVisitor {
public:
const string func;
map<string, set<int>> func_value_indices;
using IRVisitor::visit;
void visit(const Call *call) override {
IRVisitor::visit(call);
if ((call->call_type == Call::Halide) && call->func.defined()) {
func_value_indices[call->name].insert(call->value_index);
}
}
};
// Visitor and helper function to test if a piece of IR uses an extern image.
class UsesExternImage : public IRVisitor {
using IRVisitor::visit;
void visit(const Call *c) override {
if (c->call_type == Call::Image) {
result = true;
} else {
IRVisitor::visit(c);
}
}
public:
UsesExternImage() = default;
bool result = false;
};
inline bool uses_extern_image(const Stmt &s) {
UsesExternImage uses;
s.accept(&uses);
return uses.result;
}
class SplitTuples : public IRMutator {
using IRMutator::visit;
map<string, set<int>> func_value_indices;
Stmt visit(const Realize *op) override {
ScopedBinding<int> bind(realizations, op->name, 0);
if (op->types.size() > 1) {
// Make a nested set of realize nodes for each tuple element
Stmt body = mutate(op->body);
for (int i = (int)op->types.size() - 1; i >= 0; i--) {
body = Realize::make(op->name + "." + std::to_string(i),
{op->types[i]}, op->memory_type,
op->bounds, op->condition, body);
}
return body;
} else {
return IRMutator::visit(op);
}
}
Stmt visit(const For *op) override {
FindCallValueIndices find;
op->body.accept(&find);
ScopedValue<map<string, set<int>>> func_value_indices_v(func_value_indices, find.func_value_indices);
return IRMutator::visit(op);
}
Stmt visit(const Prefetch *op) override {
if (!op->prefetch.param.defined() && (op->types.size() > 1)) {
Stmt body = mutate(op->body);
// Split the prefetch from a multi-dimensional halide tuple to
// prefetches of each tuple element. Keep only prefetches of
// elements that are actually used in the loop body.
const auto &indices = func_value_indices.find(op->name);
internal_assert(indices != func_value_indices.end());
for (const auto &idx : indices->second) {
internal_assert(idx < (int)op->types.size());
body = Prefetch::make(op->name + "." + std::to_string(idx), {op->types[(idx)]}, op->bounds, op->prefetch, op->condition, body);
}
return body;
} else {
return IRMutator::visit(op);
}
}
Expr visit(const Call *op) override {
if (op->call_type == Call::Halide) {
auto it = env.find(op->name);
internal_assert(it != env.end());
Function f = it->second;
string name = op->name;
bool changed = false;
if (f.outputs() > 1) {
name += "." + std::to_string(op->value_index);
changed = true;
}
vector<Expr> args;
for (const Expr &e : op->args) {
args.push_back(mutate(e));
changed = changed || !args.back().same_as(e);
}
// It's safe to hook up the pointer to the function
// unconditionally. This expr never gets held by a
// Function, so there can't be a cycle. We do this even
// for scalar provides.
if (changed) {
return Call::make(op->type, name, args, op->call_type, f.get_contents());
} else {
return op;
}
} else {
return IRMutator::visit(op);
}
}
Stmt visit_provide(const Provide *op, const Atomic *atomic) {
if (op->values.size() == 1) {
if (atomic) {
return IRMutator::visit(atomic);
} else {
return IRMutator::visit(op);
}
}
// Mutate the args
vector<Expr> args;
for (const Expr &e : op->args) {
args.push_back(mutate(e));
}
// Get the Function
auto it = env.find(op->name);
internal_assert(it != env.end());
Function f = it->second;
// For the new value of each tuple component, what existing
// tuple components does it already depend on?
vector<set<int>> dependencies(op->values.size());
for (int i = 0; i < (int)op->values.size(); i++) {
class Checker : public IRVisitor {
using IRVisitor::visit;
vector<pair<string, Expr>> lets;
void visit(const Let *op) override {
op->value.accept(this);
lets.emplace_back(op->name, op->value);
op->body.accept(this);
lets.pop_back();
}
void visit(const Call *op) override {
if (op->call_type == Call::Halide &&
op->name == func_name &&
could_alias(op->args, store_args)) {
deps.insert(op->value_index);
}
}
bool could_alias(const vector<Expr> &a, const vector<Expr> &b) {
internal_assert(a.size() == b.size());
// Construct a boolean Expr that says the addresses are equal
Expr aliases = const_true();
for (size_t i = 0; i < a.size(); i++) {
aliases = aliases && (a[i] == b[i]);
}
// Might need some of the containing lets
for (auto it = lets.rbegin(); it != lets.rend(); it++) {
if (expr_uses_var(aliases, it->first)) {
aliases = Let::make(it->first, it->second, aliases);
}
}
return !can_prove(!aliases);
}
public:
set<int> &deps;
const string &func_name;
const vector<Expr> &store_args;
Checker(set<int> &deps,
const string &func_name,
const vector<Expr> &store_args)
: deps(deps), func_name(func_name), store_args(store_args) {
}
} checker(dependencies[i], op->name, args);
op->values[i].accept(&checker);
}
// Build clusters of tuple components where two components
// belong to the same cluster if any of their loads or stores
// may alias
vector<vector<int>> clusters;
// Reserve space so that we can use pointers to clusters.
clusters.reserve(op->values.size());
for (int i = 0; i < (int)op->values.size(); i++) {
// What clusters does it already belong to?
vector<int> *owning_cluster = nullptr;
for (auto &c : clusters) {
bool belongs_to_this_cluster = false;
for (int j : c) {
if (dependencies[j].count(i) ||
dependencies[i].count(j)) {
belongs_to_this_cluster = true;
break;
}
}
if (belongs_to_this_cluster) {
if (owning_cluster) {
// It's already in a cluster! We need to merge the clusters.
owning_cluster->insert(owning_cluster->end(), c.begin(), c.end());
c.clear();
} else {
owning_cluster = &c;
c.push_back(i);
}
}
}
if (!owning_cluster) {
// Make a new cluster
clusters.emplace_back();
clusters.back().push_back(i);
}
}
// If each cluster has only a single store in it, we can use
// CAS loops or atomic adds and avoid ever needing to wrap
// things in a mutex. We express this using separate atomic
// nodes per store. If there's no mutex involved at all, then
// there's no benefit in packing things together into a single
// critical section.
bool separate_atomic_nodes_per_store =
((atomic && atomic->mutex_name.empty()) ||
(clusters.size() == op->values.size()));
// For each cluster, build a list of scalar provide
// statements, and a list of lets to wrap them.
vector<Stmt> result;
for (auto &c : clusters) {
if (c.empty()) {
continue;
}
std::sort(c.begin(), c.end());
vector<Stmt> provides;
vector<pair<string, Expr>> lets;
Stmt s;
if (c.size() == 1) {
// Just make a provide node
int i = *c.begin();
string name = op->name + "." + std::to_string(i);
s = Provide::make(name, {mutate(op->values[i])}, args);
} else {
// Make a list of let statements that compute the
// values (doing any loads), and then a block of
// provide statements that do the stores.
for (auto i : c) {
string name = op->name + "." + std::to_string(i);
string var_name = name + ".value";
Expr val = mutate(op->values[i]);
if (!is_undef(val)) {
lets.emplace_back(var_name, val);
val = Variable::make(val.type(), var_name);
}
provides.push_back(Provide::make(name, {val}, args));
}
s = Block::make(provides);
while (!lets.empty()) {
auto p = lets.back();
lets.pop_back();
s = LetStmt::make(p.first, p.second, s);
}
}
if (atomic && separate_atomic_nodes_per_store) {
s = Atomic::make(atomic->producer_name, atomic->mutex_name, s);
}
internal_assert(s.defined());
result.push_back(s);
}
{
Stmt s = Block::make(result);
if (atomic && !separate_atomic_nodes_per_store) {
s = Atomic::make(atomic->producer_name, atomic->mutex_name, s);
}
return s;
}
}
Stmt visit(const Provide *op) override {
return visit_provide(op, nullptr);
}
Stmt visit(const Atomic *op) override {
// At this point in lowering, the only child of an atomic node
// should be a single provide node. We haven't many any
// statement mutations yet that would put things in between
// the provide and the atomic.
if (const Provide *p = op->body.as<Provide>()) {
return visit_provide(p, op);
} else {
return IRMutator::visit(op);
}
}
const map<string, Function> &env;
Scope<int> realizations;
public:
SplitTuples(const map<string, Function> &e)
: env(e) {
}
};
class SplitScatterGather : public IRMutator {
using IRMutator::visit;
// The enclosing producer node. Used for error messages.
const ProducerConsumer *producer = nullptr;
class GetScatterGatherSize : public IRVisitor {
bool permitted = true;
using IRVisitor::visit;
void visit(const Call *op) override {
if (op->is_intrinsic(Call::scatter_gather)) {
user_assert(permitted)
<< "Can't nest an expression tuple inside another in definition of "
<< producer_name;
if (result == 0) {
result = (int)op->args.size();
} else {
user_assert((int)op->args.size() == result)
<< "Expression tuples of mismatched sizes used in definition of "
<< producer_name << ": " << result << " vs " << op->args.size();
}
// No nesting tuples
permitted = false;
IRVisitor::visit(op);
permitted = true;
} else {
IRVisitor::visit(op);
}
}
public:
string producer_name;
int result = 0;
} get_scatter_gather_size_visitor;
int get_scatter_gather_size(const IRNode *op) {
if (producer) {
get_scatter_gather_size_visitor.producer_name = producer->name;
}
get_scatter_gather_size_visitor.result = 0;
op->accept(&get_scatter_gather_size_visitor);
// Maybe the user did something like jam a gather op into a
// constraint or tile size, so this is a user_assert.
user_assert(producer || get_scatter_gather_size_visitor.result == 0)
<< "scatter/gather expression used outside of a Func definition";
return get_scatter_gather_size_visitor.result;
}
class ExtractScatterGatherElement : public IRMutator {
using IRMutator::visit;
Expr visit(const Call *op) override {
if (op->is_intrinsic(Call::scatter_gather)) {
// No need to recursively mutate because we've
// already asserted that these aren't nested.
internal_assert(idx < (int)op->args.size());
return op->args[idx];
} else {
return IRMutator::visit(op);
}
}
public:
int idx;
} extractor;
Stmt visit(const ProducerConsumer *op) override {
ScopedValue<const ProducerConsumer *> old(producer, op->is_producer ? op : producer);
return IRMutator::visit(op);
}
Stmt visit_gather_let_stmt(const LetStmt *op, int size) {
// Split this variable into the gather components
vector<pair<string, Expr>> lets;
vector<Expr> vars;
for (extractor.idx = 0; extractor.idx < size; extractor.idx++) {
string name = unique_name(op->name + "." + std::to_string(extractor.idx));
lets.emplace_back(name, extractor.mutate(op->value));
vars.push_back(Variable::make(op->value.type(), name));
}
Stmt body = op->body;
Expr gather_replacement = Call::make(op->value.type(),
Call::scatter_gather,
vars,
Call::PureIntrinsic);
body = substitute(op->name, gather_replacement, body);
body = mutate(body);
for (auto it = lets.rbegin(); it != lets.rend(); it++) {
body = LetStmt::make(it->first, it->second, body);
}
return body;
}
Stmt visit(const LetStmt *op) override {
vector<pair<string, Expr>> lets;
int size = 0;
Stmt body;
do {
body = op->body;
size = get_scatter_gather_size(op->value.get());
if (size != 0) {
break;
}
lets.emplace_back(op->name, op->value);
op = body.as<LetStmt>();
} while (op);
if (size) {
internal_assert(op);
body = visit_gather_let_stmt(op, size);
} else {
internal_assert(op == nullptr);
body = mutate(body);
}
for (auto it = lets.rbegin(); it != lets.rend(); it++) {
body = LetStmt::make(it->first, it->second, body);
}
return body;
}
Stmt visit(const Provide *op) override {
int size = get_scatter_gather_size(op);
if (size == 0) {
return IRMutator::visit(op);
}
// The LHS should contain at least one scatter op, or our scatters
// all go to the same place. Is it worth asserting this? It
// could be a bug, or it could be some sort of degenerate base case.
// Fork the args and the RHS into their various versions
vector<Stmt> provides;
vector<string> names;
vector<Expr> exprs;
for (extractor.idx = 0; extractor.idx < size; extractor.idx++) {
vector<Expr> args = op->args;
for (Expr &a : args) {
string name = unique_name('t');
exprs.push_back(extractor.mutate(a));
names.push_back(name);
a = Variable::make(a.type(), name);
}
vector<Expr> values = op->values;
for (Expr &v : values) {
v = extractor.mutate(v);
string name = unique_name('t');
exprs.push_back(extractor.mutate(v));
names.push_back(name);
v = Variable::make(v.type(), name);
}
provides.push_back(Provide::make(op->name, values, args));
}
Stmt s = Block::make(provides);
// We just duplicated all the non-scatter/gather stuff too,
// so do joint CSE on the exprs
Expr bundle = Call::make(Int(32), Call::bundle, exprs, Call::PureIntrinsic);
bundle = common_subexpression_elimination(bundle);
vector<pair<string, Expr>> lets;
while (const Let *let = bundle.as<Let>()) {
lets.emplace_back(let->name, let->value);
bundle = let->body;
}
const Call *c = bundle.as<Call>();
internal_assert(c && c->is_intrinsic(Call::bundle));
for (size_t i = 0; i < exprs.size(); i++) {
if (is_pure(c->args[i])) {
// names[i] is only used once, so if the value is pure
// it should be substituted in
s = substitute(names[i], c->args[i], s);
} else {
lets.emplace_back(names[i], c->args[i]);
}
}
for (auto it = lets.rbegin(); it != lets.rend(); it++) {
s = LetStmt::make(it->first, it->second, s);
}
return s;
}
};
} // namespace
Stmt split_tuples(const Stmt &stmt, const map<string, Function> &env) {
Stmt s = SplitTuples(env).mutate(stmt);
s = SplitScatterGather().mutate(s);
return s;
}
} // namespace Internal
} // namespace Halide
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