IRMutator.h

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#ifndef HALIDE_IR_MUTATOR_H
#define HALIDE_IR_MUTATOR_H
 
/** \file
 * Defines a base class for passes over the IR that modify it
 */
 
#include <map>
 
#include "IR.h"
 
namespace Halide {
namespace Internal {
 
/** A base class for passes over the IR which modify it
 * (e.g. replacing a variable with a value (Substitute.h), or
 * constant-folding).
 *
 * Your mutator should override the visit() methods you care about and return
 * the new expression or stmt. The default implementations recursively
 * mutate their children. To mutate sub-expressions and sub-statements you
 * should override the mutate() method, which will dispatch to
 * the appropriate visit() method and then return the value of expr or
 * stmt after the call to visit.
 */
class IRMutator {
public:
    IRMutator() = default;
    virtual ~IRMutator() = default;
 
    /** This is the main interface for using a mutator. Also call
     * these in your subclass to mutate sub-expressions and
     * sub-statements.
     */
    virtual Expr mutate(const Expr &expr);
    virtual Stmt mutate(const Stmt &stmt);
 
    // Mutate all the Exprs and return the new list in ret, along with
    // a flag that is true iff at least one item in the list changed.
    std::pair<std::vector<Expr>, bool> mutate_with_changes(const std::vector<Expr> &);
 
    // Like mutate_with_changes, but discard the changes flag.
    std::vector<Expr> mutate(const std::vector<Expr> &exprs) {
        return mutate_with_changes(exprs).first;
    }
 
protected:
    // ExprNode<> and StmtNode<> are allowed to call visit (to implement mutate_expr/mutate_stmt())
    template<typename T>
    friend struct ExprNode;
    template<typename T>
    friend struct StmtNode;
 
    virtual Expr visit(const IntImm *);
    virtual Expr visit(const UIntImm *);
    virtual Expr visit(const FloatImm *);
    virtual Expr visit(const StringImm *);
    virtual Expr visit(const Cast *);
    virtual Expr visit(const Reinterpret *);
    virtual Expr visit(const Variable *);
    virtual Expr visit(const Add *);
    virtual Expr visit(const Sub *);
    virtual Expr visit(const Mul *);
    virtual Expr visit(const Div *);
    virtual Expr visit(const Mod *);
    virtual Expr visit(const Min *);
    virtual Expr visit(const Max *);
    virtual Expr visit(const EQ *);
    virtual Expr visit(const NE *);
    virtual Expr visit(const LT *);
    virtual Expr visit(const LE *);
    virtual Expr visit(const GT *);
    virtual Expr visit(const GE *);
    virtual Expr visit(const And *);
    virtual Expr visit(const Or *);
    virtual Expr visit(const Not *);
    virtual Expr visit(const Select *);
    virtual Expr visit(const Load *);
    virtual Expr visit(const Ramp *);
    virtual Expr visit(const Broadcast *);
    virtual Expr visit(const Call *);
    virtual Expr visit(const Let *);
    virtual Expr visit(const Shuffle *);
    virtual Expr visit(const VectorReduce *);
 
    virtual Stmt visit(const LetStmt *);
    virtual Stmt visit(const AssertStmt *);
    virtual Stmt visit(const ProducerConsumer *);
    virtual Stmt visit(const For *);
    virtual Stmt visit(const Store *);
    virtual Stmt visit(const Provide *);
    virtual Stmt visit(const Allocate *);
    virtual Stmt visit(const Free *);
    virtual Stmt visit(const Realize *);
    virtual Stmt visit(const Block *);
    virtual Stmt visit(const IfThenElse *);
    virtual Stmt visit(const Evaluate *);
    virtual Stmt visit(const Prefetch *);
    virtual Stmt visit(const Acquire *);
    virtual Stmt visit(const Fork *);
    virtual Stmt visit(const Atomic *);
};
 
/** A mutator that caches and reapplies previously-done mutations, so
 * that it can handle graphs of IR that have not had CSE done to
 * them. */
class IRGraphMutator : public IRMutator {
protected:
    std::map<Expr, Expr, ExprCompare> expr_replacements;
    std::map<Stmt, Stmt, Stmt::Compare> stmt_replacements;
 
public:
    Stmt mutate(const Stmt &s) override;
    Expr mutate(const Expr &e) override;
 
    std::vector<Expr> mutate(const std::vector<Expr> &exprs) {
        return IRMutator::mutate(exprs);
    }
};
 
/** A helper function for mutator-like things to mutate regions */
template<typename Mutator, typename... Args>
std::pair<Region, bool> mutate_region(Mutator *mutator, const Region &bounds, Args &&...args) {
    Region new_bounds(bounds.size());
    bool bounds_changed = false;
 
    for (size_t i = 0; i < bounds.size(); i++) {
        Expr old_min = bounds[i].min;
        Expr old_extent = bounds[i].extent;
        Expr new_min = mutator->mutate(old_min, std::forward<Args>(args)...);
        Expr new_extent = mutator->mutate(old_extent, std::forward<Args>(args)...);
        if (!new_min.same_as(old_min)) {
            bounds_changed = true;
        }
        if (!new_extent.same_as(old_extent)) {
            bounds_changed = true;
        }
        new_bounds[i] = Range(new_min, new_extent);
    }
    return {new_bounds, bounds_changed};
}
 
}  // namespace Internal
}  // namespace Halide
 
#endif