AbstractGenerator.h

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#ifndef HALIDE_ABSTRACT_GENERATOR_H_
#define HALIDE_ABSTRACT_GENERATOR_H_
 
#include <functional>
#include <map>
#include <string>
#include <vector>
 
#include "Callable.h"
#include "Expr.h"
#include "Func.h"
#include "Module.h"
#include "Parameter.h"
#include "Pipeline.h"
#include "Schedule.h"
#include "Target.h"
#include "Type.h"
 
namespace Halide {
 
class GeneratorContext;
using GeneratorParamsMap = std::map<std::string, std::string>;
 
namespace Internal {
 
enum class ArgInfoKind { Scalar,
                         Function,
                         Buffer };
 
enum class ArgInfoDirection { Input,
                              Output };
 
/**
 * AbstractGenerator is an ABC that defines the API a Generator must provide
 * to work with the existing Generator infrastructure (GenGen, RunGen, execute_generator(),
 * Generator Stubs). The existing Generator<>-based instances all implement
 * this API, but any other code that implements this (and uses RegisterGenerator
 * to register itself) should be indistinguishable from a user perspective.
 *
 * An AbstractGenerator is meant to be "single-use"; typically lifetimes will be
 * something like:
 * - create an instance (with a specific Target)
 * - optionally set GeneratorParam values
 * - optionally re-bind inputs (if using in JIT or Stub modes)
 * - call build_pipeline()
 * - optionally call output_func() to get the output(s) (if using in JIT or Stub modes)
 * - discard the instance
 *
 * AbstractGenerators should be fairly cheap to instantiate! Don't try to re-use
 * one by re-setting inputs and calling build_pipeline() multiple times.
 *
 * Note that an AbstractGenerator instance is (generally) stateful in terms of the order
 * that methods should be called; calling the methods out of order may cause
 * assert-fails or other undesirable behavior. Read the method notes carefully!
 */
class AbstractGenerator {
public:
    virtual ~AbstractGenerator() = default;
 
    /** ArgInfo is a struct to contain name-and-type information for the inputs and outputs to
     * the Pipeline that build_pipeline() will return.
     *
     * Note that this looks rather similar to Halide::Argument, but unfortunately
     * that is not a good fit here, as it cannot represent Func inputs (only
     * Buffer and Scalar), nor can it really handle Outputs.
     */
    struct ArgInfo {
        std::string name;
        ArgInfoDirection dir = ArgInfoDirection::Input;
        ArgInfoKind kind = ArgInfoKind::Scalar;
        // Note that this can have multiple entries for Tuple-valued Inputs or Outputs
        std::vector<Type> types;
        int dimensions = 0;
    };
 
    /** Return the name of this Generator. (This should always be the name
     * used to register it.) */
    virtual std::string name() = 0;
 
    /** Return the Target and autoscheduler info that this Generator
     * was created with. Always legal to call on any AbstractGenerator instance,
     * regardless of what other methods have been called. (All AbstractGenerator instances
     * are expected to be created with immutable values for these, which can't be
     * changed for a given instance after creation. Note that Generator<> based subclasses
     * can customize Target somewhat via init_from_context(); see Generator.h for more info.)
     *
     * CALL-AFTER: any
     * CALL-BEFORE: any
     */
    virtual GeneratorContext context() const = 0;
 
    /** Return a list of all the ArgInfos for this generator. The list will be in the order
     * that the input and outputs are declared (possibly interleaved).
     * Any inputs or outputs added by a configure() method will be in the list,
     * at the end, in the order added.
     * All input and output names will be unique within a given Generator instance.
     *
     * CALL-AFTER: configure()
     * CALL-BEFORE: any
     */
    virtual std::vector<ArgInfo> arginfos() = 0;
 
    /** Set the value for a specific GeneratorParam for an AbstractGenerator instance.
     *
     * Names that aren't known generator names should assert-fail.
     *
     * Values that can't be parsed for the specific GeneratorParam (e.g. passing "foo" where
     * an integer is expected) should assert-fail at some point (either immediately, or when
     * build_pipeline() is called)
     *
     * This can be called multiple times, but only prior to build_pipeline().
     *
     * CALL-AFTER: none
     * CALL-BEFORE: build_pipeline
     */
    // @{
    virtual void set_generatorparam_value(const std::string &name, const std::string &value) = 0;
    virtual void set_generatorparam_value(const std::string &name, const LoopLevel &loop_level) = 0;
    // @}
 
    /** Build and return the Pipeline for this AbstractGenerator. This method should be called
     * only once per instance.
     *
     * CALL-AFTER: set_generatorparam_value, bind_input
     * CALL-BEFORE: input_parameter, output_func, external_code_map
     */
    virtual Pipeline build_pipeline() = 0;
 
    /** Given the name of an input, return the Parameter(s) for that input.
     * (Most inputs will have exactly one, but inputs that are declared as arrays
     * will have multiple.)
     *
     * CALL-AFTER: build_pipeline
     * CALL-BEFORE: none
     */
    virtual std::vector<Parameter> input_parameter(const std::string &name) = 0;
 
    /** Given the name of an output, return the Func(s) for that output.
     *
     * Most outputs will have exactly one, but outputs that are declared as arrays will have multiple.
     *
     * Note that outputs with Tuple values are still just a single Func, though they do get realized
     * as multiple Buffers.
     *
     * Must be called after build_pipeline(), since the output Funcs will be undefined prior to that.
     *
     * CALL-AFTER: build_pipeline()
     * CALL-BEFORE: none
     */
    virtual std::vector<Func> output_func(const std::string &name) = 0;
 
    /** Rebind a specified Input to refer to the given piece of IR, replacing the
     * default ImageParam / Param in place for that Input. Basic type-checking is
     * done to ensure that inputs are still sane (e.g. types, dimensions, etc must match expectations).
     *
     * CALL-AFTER: set_generatorparam_value
     * CALL-BEFORE: build_pipeline
     */
    // @{
    virtual void bind_input(const std::string &name, const std::vector<Parameter> &v) = 0;
    virtual void bind_input(const std::string &name, const std::vector<Func> &v) = 0;
    virtual void bind_input(const std::string &name, const std::vector<Expr> &v) = 0;
    // @}
 
    /** Emit a Generator Stub (.stub.h) file to the given path. Not all Generators support this.
     *
     * If you call this method, you should not call any other AbstractGenerator methods
     * on this instance, before or after this call.
     *
     * If the Generator is capable of emitting a Stub, do so and return true. (Errors
     * during stub emission should assert-fail rather than returning false.)
     *
     * If the Generator is not capable of emitting a Stub, do nothing and return false.
     *
     * CALL-AFTER: none
     * CALL-BEFORE: none
     */
    virtual bool emit_cpp_stub(const std::string &stub_file_path) = 0;
 
    // Below are some concrete methods that build on top of the rest of the AbstractGenerator API.
    // Note that they are nonvirtual. TODO: would these be better as freestanding methods that
    // just take AbstractGeneratorPtr as arguments?
 
    /** Call generate() and produce a Module for the result.
     *If function_name is empty, generator_name() will be used for the function. */
    Module build_module(const std::string &function_name = "");
 
    /**
     * Build a module that is suitable for using for gradient descent calculation in TensorFlow or PyTorch.
     *
     * Essentially:
     *   - A new Pipeline is synthesized from the current Generator (according to the rules below)
     *   - The new Pipeline is autoscheduled (if autoscheduling is requested, but it would be odd not to do so)
     *   - The Pipeline is compiled to a Module and returned
     *
     * The new Pipeline is adjoint to the original; it has:
     *   - All the same inputs as the original, in the same order
     *   - Followed by one grad-input for each original output
     *   - Followed by one output for each unique pairing of original-output + original-input.
     *     (For the common case of just one original-output, this amounts to being one output for each original-input.)
     */
    Module build_gradient_module(const std::string &function_name);
 
    /**
     * JIT the AbstractGenerator into a Callable (using the currently-set
     * Target) and return it.
     *
     * If jit_handlers is not null, set the jitted func's jit_handlers to use a copy of it.
     *
     * If jit_externs is not null, use it to set the jitted func's external dependencies.
     */
    Callable compile_to_callable(const JITHandlers *jit_handlers = nullptr,
                                 const std::map<std::string, JITExtern> *jit_externs = nullptr);
 
    /*
     * Set all the GeneratorParams in the map. This is equivalent to simply calling the
     * `set_generatorparam_value()` method in a loop over the map, but is quite convenient. */
    void set_generatorparam_values(const GeneratorParamsMap &m);
};
 
using AbstractGeneratorPtr = std::unique_ptr<AbstractGenerator>;
 
}  // namespace Internal
}  // namespace Halide
 
#endif