static_arg_opt.h

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#pragma once
 
#include <fe/bitset.h>
 
#include "mim/phase.h"
 
namespace mim {
 
/// Static Argument Transformation.
/// A recursive Lam whose self-calls merely forward some of its params is split into a wrapper `wrap`
/// (same signature) and a `loop` that drops those params;
/// self-calls forwarding all of them become jumps to `loop`, all others go through `wrap`.
/// Tail recursion elimination is the special case where the dropped param is the ret var.
/// @see [Compilation by Transformation in Non-Strict Functional Languages,
/// §7](https://theses.gla.ac.uk/74568/1/10992188.pdf)
class StaticArgOpt : public RWPhase {
public:
    using RWPhase::RWPhase;
 
private:
    bool analyze() final;
    void analyze(const Def*);
    void visit(const App*, Lam*);
 
    const Def* rewrite_imm_App(const App*) final;
    const Def* rewrite_mut_Lam(Lam*) final;
 
    /// Which of @p lam's doms does the loop keep - those the selected self-calls do *not* forward unchanged?
    /// A Sieve that keeps *all* of them means: leave @p lam alone.
    Sieve sieve(Lam* lam);
 
    DefSet analyzed_;
    LamMap<fe::Vector<fe::Bitset>> lam2sites_;
    LamMap<Sieve> lam2sieve_;
    Lam2Lam old2loop_;
};
 
} // namespace mim