Revision 69e4dffe991aafe28a7457fbe7cc3978a8074020 authored by Andrew Adams on 21 February 2021, 17:31:49 UTC, committed by Andrew Adams on 21 February 2021, 17:31:49 UTC
Scope.h
#ifndef HALIDE_SCOPE_H
#define HALIDE_SCOPE_H
#include <iostream>
#include <map>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include "Debug.h"
#include "Error.h"
/** \file
* Defines the Scope class, which is used for keeping track of names in a scope while traversing IR
*/
namespace Halide {
namespace Internal {
/** A stack which can store one item very efficiently. Using this
* instead of std::stack speeds up Scope substantially. */
template<typename T>
class SmallStack {
private:
T _top;
std::vector<T> _rest;
bool _empty = true;
public:
SmallStack() = default;
void pop() {
if (_rest.empty()) {
_empty = true;
_top = T();
} else {
_top = std::move(_rest.back());
_rest.pop_back();
}
}
void push(T t) {
if (!_empty) {
_rest.push_back(std::move(_top));
}
_top = std::move(t);
_empty = false;
}
T top() const {
return _top;
}
T &top_ref() {
return _top;
}
const T &top_ref() const {
return _top;
}
bool empty() const {
return _empty;
}
size_t size() const {
return _empty ? 0 : (_rest.size() + 1);
}
};
template<>
class SmallStack<void> {
// A stack of voids. Voids are all the same, so just record how many voids are in the stack
int counter = 0;
public:
void pop() {
counter--;
}
void push() {
counter++;
}
bool empty() const {
return counter == 0;
}
};
/** A common pattern when traversing Halide IR is that you need to
* keep track of stuff when you find a Let or a LetStmt, and that it
* should hide previous values with the same name until you leave the
* Let or LetStmt nodes This class helps with that. */
template<typename T = void>
class Scope {
private:
std::map<std::string, SmallStack<T>> table;
const Scope<T> *containing_scope = nullptr;
public:
Scope() = default;
Scope(Scope &&that) noexcept = default;
Scope &operator=(Scope &&that) noexcept = default;
// Copying a scope object copies a large table full of strings and
// stacks. Bad idea.
Scope(const Scope<T> &) = delete;
Scope<T> &operator=(const Scope<T> &) = delete;
/** Set the parent scope. If lookups fail in this scope, they
* check the containing scope before returning an error. Caller is
* responsible for managing the memory of the containing scope. */
void set_containing_scope(const Scope<T> *s) {
containing_scope = s;
}
/** A const ref to an empty scope. Useful for default function
* arguments, which would otherwise require a copy constructor
* (with llvm in c++98 mode) */
static const Scope<T> &empty_scope() {
static Scope<T> _empty_scope;
return _empty_scope;
}
/** Retrieve the value referred to by a name */
template<typename T2 = T,
typename = typename std::enable_if<!std::is_same<T2, void>::value>::type>
T2 get(const std::string &name) const {
typename std::map<std::string, SmallStack<T>>::const_iterator iter = table.find(name);
if (iter == table.end() || iter->second.empty()) {
if (containing_scope) {
return containing_scope->get(name);
} else {
internal_error << "Name not in Scope: " << name << "\n"
<< *this << "\n";
}
}
return iter->second.top();
}
/** Return a reference to an entry. Does not consider the containing scope. */
template<typename T2 = T,
typename = typename std::enable_if<!std::is_same<T2, void>::value>::type>
T2 &ref(const std::string &name) {
typename std::map<std::string, SmallStack<T>>::iterator iter = table.find(name);
if (iter == table.end() || iter->second.empty()) {
internal_error << "Name not in Scope: " << name << "\n"
<< *this << "\n";
}
return iter->second.top_ref();
}
/** Tests if a name is in scope */
bool contains(const std::string &name) const {
typename std::map<std::string, SmallStack<T>>::const_iterator iter = table.find(name);
if (iter == table.end() || iter->second.empty()) {
if (containing_scope) {
return containing_scope->contains(name);
} else {
return false;
}
}
return true;
}
/** How many nested definitions of a single name exist? */
size_t count(const std::string &name) const {
auto it = table.find(name);
if (it == table.end()) {
return 0;
} else {
return it->second.size();
}
}
/** Add a new (name, value) pair to the current scope. Hide old
* values that have this name until we pop this name.
*/
template<typename T2 = T,
typename = typename std::enable_if<!std::is_same<T2, void>::value>::type>
void push(const std::string &name, T2 &&value) {
table[name].push(std::forward<T2>(value));
}
template<typename T2 = T,
typename = typename std::enable_if<std::is_same<T2, void>::value>::type>
void push(const std::string &name) {
table[name].push();
}
/** A name goes out of scope. Restore whatever its old value
* was (or remove it entirely if there was nothing else of the
* same name in an outer scope) */
void pop(const std::string &name) {
typename std::map<std::string, SmallStack<T>>::iterator iter = table.find(name);
internal_assert(iter != table.end()) << "Name not in Scope: " << name << "\n"
<< *this << "\n";
iter->second.pop();
if (iter->second.empty()) {
table.erase(iter);
}
}
/** Iterate through the scope. Does not capture any containing scope. */
class const_iterator {
typename std::map<std::string, SmallStack<T>>::const_iterator iter;
public:
explicit const_iterator(const typename std::map<std::string, SmallStack<T>>::const_iterator &i)
: iter(i) {
}
const_iterator() = default;
bool operator!=(const const_iterator &other) {
return iter != other.iter;
}
void operator++() {
++iter;
}
const std::string &name() {
return iter->first;
}
const SmallStack<T> &stack() {
return iter->second;
}
template<typename T2 = T,
typename = typename std::enable_if<!std::is_same<T2, void>::value>::type>
const T2 &value() {
return iter->second.top_ref();
}
};
const_iterator cbegin() const {
return const_iterator(table.begin());
}
const_iterator cend() const {
return const_iterator(table.end());
}
void swap(Scope<T> &other) {
table.swap(other.table);
std::swap(containing_scope, other.containing_scope);
}
};
template<typename T>
std::ostream &operator<<(std::ostream &stream, const Scope<T> &s) {
stream << "{\n";
typename Scope<T>::const_iterator iter;
for (iter = s.cbegin(); iter != s.cend(); ++iter) {
stream << " " << iter.name() << "\n";
}
stream << "}";
return stream;
}
/** Helper class for pushing/popping Scope<> values, to allow
* for early-exit in Visitor/Mutators that preserves correctness.
* Note that this name can be a bit confusing, since there are two "scopes"
* involved here:
* - the Scope object itself
* - the lifetime of this helper object
* The "Scoped" in this class name refers to the latter, as it temporarily binds
* a name within the scope of this helper's lifetime. */
template<typename T = void>
struct ScopedBinding {
Scope<T> *scope = nullptr;
std::string name;
ScopedBinding() = default;
ScopedBinding(Scope<T> &s, const std::string &n, T value)
: scope(&s), name(n) {
scope->push(name, std::move(value));
}
ScopedBinding(bool condition, Scope<T> &s, const std::string &n, const T &value)
: scope(condition ? &s : nullptr), name(n) {
if (condition) {
scope->push(name, value);
}
}
bool bound() const {
return scope != nullptr;
}
~ScopedBinding() {
if (scope) {
scope->pop(name);
}
}
// allow move but not copy
ScopedBinding(const ScopedBinding &that) = delete;
ScopedBinding(ScopedBinding &&that) noexcept
: scope(that.scope),
name(std::move(that.name)) {
// The move constructor must null out scope, so we don't try to pop it
that.scope = nullptr;
}
void operator=(const ScopedBinding &that) = delete;
void operator=(ScopedBinding &&that) = delete;
};
template<>
struct ScopedBinding<void> {
Scope<> *scope;
std::string name;
ScopedBinding(Scope<> &s, const std::string &n)
: scope(&s), name(n) {
scope->push(name);
}
ScopedBinding(bool condition, Scope<> &s, const std::string &n)
: scope(condition ? &s : nullptr), name(n) {
if (condition) {
scope->push(name);
}
}
~ScopedBinding() {
if (scope) {
scope->pop(name);
}
}
// allow move but not copy
ScopedBinding(const ScopedBinding &that) = delete;
ScopedBinding(ScopedBinding &&that) noexcept
: scope(that.scope),
name(std::move(that.name)) {
// The move constructor must null out scope, so we don't try to pop it
that.scope = nullptr;
}
void operator=(const ScopedBinding &that) = delete;
void operator=(ScopedBinding &&that) = delete;
};
} // namespace Internal
} // namespace Halide
#endif
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