Substitute.h

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#ifndef HALIDE_SUBSTITUTE_H
#define HALIDE_SUBSTITUTE_H
 
/** \file
 *
 * Defines methods for substituting out variables in expressions and
 * statements. */
 
#include <algorithm>
#include <iterator>
#include <map>
 
#include "Expr.h"
 
namespace Halide {
namespace Internal {
 
/** Substitute variables with the given name with the replacement
 * expression within expr. This is a dangerous thing to do if variable
 * names have not been uniquified. While it won't traverse inside let
 * statements with the same name as the first argument, moving a piece
 * of syntax around can change its meaning, because it can cross lets
 * that redefine variable names that it includes references to. */
Expr substitute(const std::string &name, const Expr &replacement, const Expr &expr);
 
/** Substitute variables with the given name with the replacement
 * expression within stmt. */
Stmt substitute(const std::string &name, const Expr &replacement, const Stmt &stmt);
 
/** Substitute variables with names in the map. */
// @{
Expr substitute(const std::map<std::string, Expr> &replacements, const Expr &expr);
Stmt substitute(const std::map<std::string, Expr> &replacements, const Stmt &stmt);
// @}
 
/** Substitute expressions for other expressions. */
// @{
Expr substitute(const Expr &find, const Expr &replacement, const Expr &expr);
Stmt substitute(const Expr &find, const Expr &replacement, const Stmt &stmt);
// @}
 
/** Substitute a container of Exprs or Stmts out of place */
template<typename T>
T substitute(const std::map<std::string, Expr> &replacements, const T &container) {
    T output;
    std::transform(container.begin(), container.end(), std::back_inserter(output), [&](const auto &expr_or_stmt) {
        return substitute(replacements, expr_or_stmt);
    });
    return output;
}
 
/** Substitutions where the IR may be a general graph (and not just a
 * DAG). */
// @{
Expr graph_substitute(const std::string &name, const Expr &replacement, const Expr &expr);
Stmt graph_substitute(const std::string &name, const Expr &replacement, const Stmt &stmt);
Expr graph_substitute(const Expr &find, const Expr &replacement, const Expr &expr);
Stmt graph_substitute(const Expr &find, const Expr &replacement, const Stmt &stmt);
// @}
 
/** Substitute in all let Exprs in a piece of IR. Doesn't substitute
 * in let stmts, as this may change the meaning of the IR (e.g. by
 * moving a load after a store). Produces graphs of IR, so don't use
 * non-graph-aware visitors or mutators on it until you've CSE'd the
 * result. */
// @{
Expr substitute_in_all_lets(const Expr &expr);
Stmt substitute_in_all_lets(const Stmt &stmt);
// @}
 
}  // namespace Internal
}  // namespace Halide
 
#endif