libcilkrts/runtime/config/generic/cilk-abi-vla.c

/* cilk-abi-vla.cpp                  -*-C++-*-
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/*
 * Implementation of Variable Length Array (VLA) ABI.
 *
 * The compiler calls these functions to allocate Variable Length Arrays
 * at runtime.  The compiler must guarantee that __cilkrts_stack_free() is
 * called to cleanup any memory allocated by __cilkrts_stack_alloc().
 *
 * This generic implementation always allocates the memory from the heap.
 * Optimally, the implementation should expand the frame of the calling
 * function if possible, since that will be faster.  See the x86 version
 * for one possible implementation.
 */

#include <assert.h>
#include <stdlib.h>
#include <stdint.h>

#include "internal/abi.h"
#include "cilk-abi-vla-internal.h"

#define c_cilk_ptr_from_heap  0xc2f2f00d
#define c_cilk_ptr_from_stack 0xc3f30d0f

// Allocate space for a variable length array
CILK_ABI(__cilkrts_void_ptr)
__cilkrts_stack_alloc(
    __cilkrts_stack_frame *sf,
    size_t size,
    size_t distance_from_sp_to_alloca_area,
    uint32_t align,     // align is always >= minimum stack alignment and
                        // >= ptr_size as well, and must be a power of 2.
    uint32_t needs_tag  // non-zero if the pointer being returned needs to
                        // be tagged
)
{
    // full_size will be a multiple of align, and contains
    // enough extra space to allocate a marker.
    size_t full_size = (size + align - 1) & ~(align - 1);

    // Allocate memory from the heap.  The compiler is responsible
    // for guaranteeing us a chance to free it before the function
    // exits

    return (void *)vla_internal_heap_alloc(sf, full_size, align);
}

// Free the space allocated for a variable length array.
CILK_ABI(void)
__cilkrts_stack_free(
    __cilkrts_stack_frame *sf,
    void *p,
    size_t size,
    size_t distance_from_sp_to_alloca_area,
    uint32_t align, // same requirements as for align in allocation,
                    // and must match alignment that was passed when
                    // doing the allocation 
    uint32_t known_from_stack  // non-zero if this is known to be allocated
                               // on the stack, and therefore has no tag
)
{
    // full_size will be a multiple of align, and contains
    // enough extra space to allocate a marker if one was needed.
    size_t full_size = (size + align - 1) & ~(align - 1);

    // Just free the allocated memory to the heap since we don't know
    // how to expand/contract the calling frame
    vla_internal_heap_free(p, full_size);
}