CodeGen_Posix.h

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#ifndef HALIDE_CODEGEN_POSIX_H
#define HALIDE_CODEGEN_POSIX_H
 
/** \file
 * Defines a base-class for code-generators on posixy cpu platforms
 */
 
#include "CodeGen_LLVM.h"
 
namespace Halide {
namespace Internal {
 
/** A code generator that emits posix code from a given Halide stmt. */
class CodeGen_Posix : public CodeGen_LLVM {
public:
    /** Create an posix code generator. Processor features can be
     * enabled using the appropriate arguments */
    CodeGen_Posix(const Target &t);
 
protected:
    using CodeGen_LLVM::visit;
 
    /** Posix implementation of Allocate. Small constant-sized allocations go
     * on the stack. The rest go on the heap by calling "halide_malloc"
     * and "halide_free" in the standard library. */
    // @{
    void visit(const Allocate *) override;
    void visit(const Free *) override;
    // @}
 
    /** A struct describing heap or stack allocations. */
    struct Allocation {
        /** The memory */
        llvm::Value *ptr = nullptr;
 
        /** Destructor stack slot for this allocation. */
        llvm::Value *destructor = nullptr;
 
        /** Function to accomplish the destruction. */
        llvm::Function *destructor_function = nullptr;
 
        /** Pseudostack slot for this allocation. Non-null for
         * allocations of type Stack with dynamic size. */
        llvm::Value *pseudostack_slot = nullptr;
 
        /** The (Halide) type of the allocation. */
        Type type;
 
        /** How many bytes this allocation is, or 0 if not
         * constant. */
        int constant_bytes = 0;
 
        /** How many bytes of stack space used. 0 implies it was a
         * heap allocation. */
        int stack_bytes = 0;
 
        /** A unique name for this allocation. May not be equal to the
         * Allocate node name in cases where we detect multiple
         * Allocate nodes can share a single allocation. */
        std::string name;
    };
 
    /** The allocations currently in scope. The stack gets pushed when
     * we enter a new function. */
    Scope<Allocation> allocations;
 
    std::string get_allocation_name(const std::string &n) override;
 
private:
    /** Stack allocations that were freed, but haven't gone out of
     * scope yet.  This allows us to re-use stack allocations when
     * they aren't being used. */
    std::vector<Allocation> free_stack_allocs;
 
    /** current size of all alloca instances in use; this is tracked only
     * for debug output purposes. */
    size_t cur_stack_alloc_total{0};
 
    /** Generates code for computing the size of an allocation from a
     * list of its extents and its size. Fires a runtime assert
     * (halide_error) if the size overflows 2^31 -1, the maximum
     * positive number an int32_t can hold. */
    llvm::Value *codegen_allocation_size(const std::string &name, Type type, const std::vector<Expr> &extents, const Expr &condition);
 
    /** Allocates some memory on either the stack or the heap, and
     * returns an Allocation object describing it. For heap
     * allocations this calls halide_malloc in the runtime, and for
     * stack allocations it either reuses an existing block from the
     * free_stack_blocks list, or it saves the stack pointer and calls
     * alloca.
     *
     * This call returns the allocation, pushes it onto the
     * 'allocations' map, and adds an entry to the symbol table called
     * name.host that provides the base pointer.
     *
     * When the allocation can be freed call 'free_allocation', and
     * when it goes out of scope call 'destroy_allocation'. */
    Allocation create_allocation(const std::string &name, Type type, MemoryType memory_type,
                                 const std::vector<Expr> &extents, const Expr &condition,
                                 const Expr &new_expr, std::string free_function, int padding);
 
    /** Free an allocation previously allocated with
     * create_allocation */
    void free_allocation(const std::string &name);
};
 
}  // namespace Internal
}  // namespace Halide
 
#endif