heap2stack.h

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#pragma once
 
#include "mim/plug/mem/escape_analysis.h"
 
namespace mim::plug::mem::phase {
 
/// Turns a `mem.alloc` that does not escape its function (see mem::EscapeAnalysis) into a `mem.slot`.
///
/// The slot's continuation receives the remainder of the alloc's home.
/// Only allocations of at most `-X mem:heap2stack=<n>` elements in address space 0 qualify; `0` disables this phase.
/// A slot lives until its function returns, so an alloc in a loop of its function stays on the heap.
/// A `mem.free` of a converted alloc is dropped.
class Heap2Stack : public RWPhase {
public:
    Heap2Stack(World&, flags_t annex);
 
private:
    bool analyze() final;
    const Def* rewrite_imm_App(const App*) final;
 
    /// The number of scalars in @p type; `std::nullopt` if not statically known or more than `max_`.
    std::optional<nat_t> num_elems(const Def* type) const;
 
    EscapeAnalysis escape_;
    const nat_t max_;
    /// Old tail ↦ the allocs on its chain to turn into slots, in program order.
    DefMap<fe::Vector<const App*>> slots_;
    DefSet converted_;
};
 
} // namespace mim::plug::mem::phase