torch/csrc/jit/script/compiler.h

#pragma once
#include <functional>
#include <memory>
#include <string>

#include "torch/csrc/jit/ir.h"
#include "torch/csrc/jit/script/error_report.h"
#include "torch/csrc/jit/script/tree_views.h"
#include "torch/csrc/jit/script/module.h"

namespace torch {
namespace jit {
namespace script {

struct CallsiteDescriptor {
  size_t n_outputs;
  bool allow_varargs;
};


// The AST can contain nodes like `self`, `self.b` or `python_fn` that
// are not first-class values in the graph representation, but instead
// will be desugared based on how they are used in the AST.

// SugaredValue is used to temporarily represent these values in a way
// that separates their behavior from the AST -> IR converter itself.
// This allows us to keep dependencies on python minimal.

struct SugaredValue : public std::enable_shared_from_this<SugaredValue> {
  // what is this node? for error reporting (e.g. Module, python function)
  virtual std::string kind() const = 0;

  // what can we do with this thing?
  // use it as a value e.g.  `this + 4`
  virtual Value * asValue(SourceRange loc, Method & m) {
    throw ErrorReport(loc) << kind() << " cannot be used as a value";
  }

  // select an attribute on it, e.g. `this.field`
  virtual std::shared_ptr<SugaredValue> attr(SourceRange loc, Method & m, const std::string& field) {
    throw ErrorReport(loc) << "attribute lookup is not defined on " << kind();
  }

  // use it as a vector of values, e.g. a tuple of values as return value from
  // a method invocation
  virtual std::vector<std::shared_ptr<SugaredValue>> asTuple(SourceRange loc, Method& m) {
    throw ErrorReport(loc) << kind() << " cannot be used as a tuple";
  }

  // call it like a function, e.g. `outputs = this(inputs)`
  virtual std::shared_ptr<SugaredValue> call(
    SourceRange loc,
    Method & m,
    at::ArrayRef<Value*> inputs,
    List<Attribute> attributes,
    size_t n_binders) {
// n_binders is always set to the number of variables an expression is
// syntactically bound to:
//     a = foo() # 1 binder (note in this case the single binder might be a tuple)
//     a, * b = foo() # 1 binder
//     a, b = foo() # 2 binders
//     foo() # 0 binders
//
// In subexpressions, like bar() in foo(bar()), n_binders is always set to
// 1. n_binders is used as a hint to subexpressions to determine how many
// values they should return when that number is ambiguous statically. In
// particular it is currently used to decide how many tensors a call to a
// python function will return. It is only a hint, functions do not have to
// check that n_binders match the number of things they are returning, the
// assignment logic will do that anyway.

    throw ErrorReport(loc) << "cannot call a " << kind();
  }

  virtual ~SugaredValue() {}
};

// most things in the environment are just simple value types
// and not special python syntax sugar types
struct SimpleValue : public SugaredValue {
  SimpleValue(Value * value)
  : value(value) {}
  virtual std::string kind() const override {
    return "value";
  }
  virtual Value * asValue(SourceRange range, Method & m) override {
    return value;
  }
  virtual std::vector<std::shared_ptr<SugaredValue>> asTuple(SourceRange loc, Method& m) override;
  virtual std::shared_ptr<SugaredValue> attr(SourceRange loc, Method & m, const std::string& field) override;
  Value* getValue() const {
    return value;
  }
private:
  Value* value;
};

struct BuiltinFunction : public SugaredValue {
  BuiltinFunction(const std::string& name, Value* value=nullptr)
    : name(name), value(value) {}
  std::string name;
  Value* value;

  virtual std::string kind() const override {
    return "builtin";
  }
  virtual std::shared_ptr<SugaredValue> call(
    SourceRange loc,
    Method & m,
    at::ArrayRef<Value*> inputs_,
    List<Attribute> attributes,
    size_t n_binders) override;
};

using Resolver = std::function<std::shared_ptr<SugaredValue>(const std::string& name)>;
void defineMethodsInModule(
  Module & m,
  const std::vector<Def>& definitions,
  const Resolver& resolver, /* determines how we handle free variables*/
  std::shared_ptr<SugaredValue> self /* if non-null, the first argument to each def, is bound to this value */
);

// same as above but parse the definitions from source
void defineMethodsInModule(Module & m, const std::string& source, const Resolver& resolver, std::shared_ptr<SugaredValue> self);
std::shared_ptr<Graph> compileFunction(Def def, const Resolver& resolver);

// pack outputs of a function following python rules. If there is a single value return
// a SimpleValue, otherwise pack all the values into a Tuple.
std::shared_ptr<SugaredValue> packOutputs(Graph& g, at::ArrayRef<Value*> values);
std::vector<Value*> inlineCallTo(Graph& g, Graph& callee, ArrayRef<Value*> inputs);


} // namespace script
} // namespace jit
} // namespace torch