opencl backend: print kernel file using single printer

[ppcg.git] / opencl.c

/*
 * Copyright 2013      Ecole Normale Superieure
 *
 * Use of this software is governed by the GNU LGPLv2.1 license
 *
 * Written by Sven Verdoolaege and Riyadh Baghdadi,
 * Ecole Normale Superieure, 45 rue d’Ulm, 75230 Paris, France
 */

#include <ctype.h>
#include <limits.h>
#include <string.h>

#include <isl/aff.h>
#include <isl/ast.h>

#include "opencl.h"
#include "gpu_print.h"
#include "gpu.h"
#include "ppcg.h"
#include "print.h"
#include "schedule.h"

#define min(a, b)  (((a) < (b)) ? (a) : (b))
#define max(a, b)  (((a) > (b)) ? (a) : (b))

/* options are the global options passed to generate_opencl.
 * input is the name of the input file.
 * output is the user-specified output file name and may be NULL
 *      if not specified by the user.
 * kernel_c_name is the name of the kernel_c file.
 * kprinter is an isl_printer for the kernel file.
 * host_c is the generated source file for the host code.  kernel_c is
 * the generated source file for the kernel.  kernel_h is the generated
 * header file for the kernel.
 */
struct opencl_info {
        struct ppcg_options *options;
        const char *input;
        const char *output;
        char kernel_c_name[PATH_MAX];

        isl_printer *kprinter;

        FILE *host_c;
        FILE *kernel_c;
        FILE *kernel_h;
};

/* Open the file called "name" for writing or print an error message.
 */
static FILE *open_or_croak(const char *name)
{
        FILE *file;

        file = fopen(name, "w");
        if (!file)
                fprintf(stderr, "Failed to open \"%s\" for writing\n", name);
        return file;
}

/* Open the host .c file and the kernel .h and .cl files for writing.
 * Their names are derived from info->output (or info->input if
 * the user did not specify an output file name).
 * Add the necessary includes to these files, including those specified
 * by the user.
 *
 * Return 0 on success and -1 on failure.
 */
static int opencl_open_files(struct opencl_info *info)
{
        char name[PATH_MAX];
        int i;
        int len;

        if (info->output) {
                const char *ext;

                ext = strrchr(info->output, '.');
                len = ext ? ext - info->output : strlen(info->output);
                memcpy(name, info->output, len);

                info->host_c = open_or_croak(info->output);
        } else {
                len = ppcg_extract_base_name(name, info->input);

                strcpy(name + len, "_host.c");
                info->host_c = open_or_croak(name);
        }

        memcpy(info->kernel_c_name, name, len);
        strcpy(info->kernel_c_name + len, "_kernel.cl");
        info->kernel_c = open_or_croak(info->kernel_c_name);

        strcpy(name + len, "_kernel.h");
        info->kernel_h = open_or_croak(name);

        if (!info->host_c || !info->kernel_c || !info->host_c)
                return -1;

        fprintf(info->host_c, "#include <assert.h>\n");
        fprintf(info->host_c, "#include <stdio.h>\n");
        fprintf(info->host_c, "#include \"%s\"\n\n", ppcg_base_name(name));
        fprintf(info->kernel_h, "#if defined(__APPLE__)\n");
        fprintf(info->kernel_h, "#include <OpenCL/opencl.h>\n");
        fprintf(info->kernel_h, "#else\n");
        fprintf(info->kernel_h, "#include <CL/opencl.h>\n");
        fprintf(info->kernel_h, "#endif\n\n");
        fprintf(info->kernel_h, "cl_device_id opencl_create_device("
                                "int use_gpu);\n");
        fprintf(info->kernel_h, "cl_program opencl_build_program("
                                "cl_context ctx, "
                                "cl_device_id dev, const char *filename, "
                                "const char *opencl_options);\n");
        fprintf(info->kernel_h,
                "const char *opencl_error_string(cl_int error);\n");
        for (i = 0; i < info->options->opencl_n_include_file; ++i) {
                info->kprinter = isl_printer_print_str(info->kprinter,
                                        "#include <");
                info->kprinter = isl_printer_print_str(info->kprinter,
                                        info->options->opencl_include_files[i]);
                info->kprinter = isl_printer_print_str(info->kprinter, ">\n");
        }

        return 0;
}

/* Write the code that we have accumulated in the kernel isl_printer to the
 * kernel.cl file.
 */
static void opencl_write_kernel_file(struct opencl_info *opencl)
{
        char *raw = isl_printer_get_str(opencl->kprinter);

        fprintf(opencl->kernel_c, "%s", raw);

        free(raw);
}

/* Close all output files.  Write the kernel contents to the kernel file before
 * closing it.
 */
static void opencl_close_files(struct opencl_info *info)
{
        if (info->kernel_c) {
                opencl_write_kernel_file(info);
                fclose(info->kernel_c);
        }
        if (info->kernel_h)
                fclose(info->kernel_h);
        if (info->host_c)
                fclose(info->host_c);
}

static __isl_give isl_printer *opencl_print_host_macros(__isl_take isl_printer *p)
{
        const char *macros =
                "#define openclCheckReturn(ret) \\\n"
                "  if (ret != CL_SUCCESS) {\\\n"
                "    fprintf(stderr, \"OpenCL error: %s\\n\", "
                "opencl_error_string(ret)); \\\n"
                "    fflush(stderr); \\\n"
                "    assert(ret == CL_SUCCESS);\\\n  }\n";

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, macros);
        p = isl_printer_end_line(p);

        p = isl_ast_op_type_print_macro(isl_ast_op_max, p);

        return p;
}

static __isl_give isl_printer *opencl_declare_device_arrays(
        __isl_take isl_printer *p, struct gpu_prog *prog)
{
        int i;

        for (i = 0; i < prog->n_array; ++i) {
                if (gpu_array_is_read_only_scalar(&prog->array[i]))
                        continue;
                p = isl_printer_start_line(p);
                p = isl_printer_print_str(p, "cl_mem dev_");
                p = isl_printer_print_str(p, prog->array[i].name);
                p = isl_printer_print_str(p, ";");
                p = isl_printer_end_line(p);
        }
        p = isl_printer_start_line(p);
        p = isl_printer_end_line(p);
        return p;
}

/* Given an array, check whether its positive size guard expression is
 * trivial.
 */
static int is_array_positive_size_guard_trivial(struct gpu_array_info *array)
{
        isl_set *guard;
        int is_trivial;

        guard = gpu_array_positive_size_guard(array);
        is_trivial = isl_set_plain_is_universe(guard);
        isl_set_free(guard);
        return is_trivial;
}

/* Allocate a device array for array and copy the contents to the device
 * if copy is set.
 *
 * Emit a max-expression to ensure the device array can contain at least one
 * element if the array's positive size guard expression is not trivial.
 */
static __isl_give isl_printer *allocate_device_array(__isl_take isl_printer *p,
        struct gpu_array_info *array, int copy)
{
        int need_lower_bound;

        p = ppcg_start_block(p);

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "dev_");
        p = isl_printer_print_str(p, array->name);
        p = isl_printer_print_str(p, " = clCreateBuffer(context, ");
        p = isl_printer_print_str(p, "CL_MEM_READ_WRITE");

        if (!copy)
                p = isl_printer_print_str(p, ", ");
        else
                p = isl_printer_print_str(p, " | CL_MEM_COPY_HOST_PTR, ");

        need_lower_bound = !is_array_positive_size_guard_trivial(array);
        if (need_lower_bound) {
                p = isl_printer_print_str(p, "max(sizeof(");
                p = isl_printer_print_str(p, array->type);
                p = isl_printer_print_str(p, "), ");
        }
        p = gpu_array_info_print_size(p, array);
        if (need_lower_bound)
                p = isl_printer_print_str(p, ")");

        if (!copy)
                p = isl_printer_print_str(p, ", NULL");
        else if (gpu_array_is_scalar(array)) {
                p = isl_printer_print_str(p, ", &");
                p = isl_printer_print_str(p, array->name);
        } else {
                p = isl_printer_print_str(p, ", ");
                p = isl_printer_print_str(p, array->name);
        }

        p = isl_printer_print_str(p, ", &err);");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn(err);");
        p = isl_printer_end_line(p);

        p = ppcg_end_block(p);

        return p;
}

/* Allocate device arrays and copy the contents of copy_in arrays into device.
 */
static __isl_give isl_printer *opencl_allocate_device_arrays(
        __isl_take isl_printer *p, struct gpu_prog *prog)
{
        int i, j;

        for (i = 0; i < prog->n_array; ++i) {
                struct gpu_array_info *array = &prog->array[i];
                isl_space *space;
                isl_set *read_i;
                int empty;

                if (gpu_array_is_read_only_scalar(array))
                        continue;

                space = isl_space_copy(array->space);
                read_i = isl_union_set_extract_set(prog->copy_in, space);
                empty = isl_set_plain_is_empty(read_i);
                isl_set_free(read_i);

                p = allocate_device_array(p, array, !empty);
        }
        p = isl_printer_start_line(p);
        p = isl_printer_end_line(p);
        return p;
}

/* Print a call to the OpenCL clSetKernelArg() function which sets
 * the arguments of the kernel.  arg_name and arg_index are the name and the
 * index of the kernel argument.  The index of the leftmost argument of
 * the kernel is 0 whereas the index of the rightmost argument of the kernel
 * is n - 1, where n is the total number of the kernel arguments.
 * read_only_scalar is a boolean that indicates whether the argument is a read
 * only scalar.
 */
static __isl_give isl_printer *opencl_set_kernel_argument(
        __isl_take isl_printer *p, int kernel_id,
        const char *arg_name, int arg_index, int read_only_scalar)
{
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p,
                "openclCheckReturn(clSetKernelArg(kernel");
        p = isl_printer_print_int(p, kernel_id);
        p = isl_printer_print_str(p, ", ");
        p = isl_printer_print_int(p, arg_index);
        p = isl_printer_print_str(p, ", sizeof(");

        if (read_only_scalar) {
                p = isl_printer_print_str(p, arg_name);
                p = isl_printer_print_str(p, "), &");
        } else
                p = isl_printer_print_str(p, "cl_mem), (void *) &dev_");

        p = isl_printer_print_str(p, arg_name);
        p = isl_printer_print_str(p, "));");
        p = isl_printer_end_line(p);

        return p;
}

/* Print the block sizes as a list of the sizes in each
 * dimension.
 */
static __isl_give isl_printer *opencl_print_block_sizes(
        __isl_take isl_printer *p, struct ppcg_kernel *kernel)
{
        int i;

        if (kernel->n_block > 0)
                for (i = 0; i < kernel->n_block; ++i) {
                        if (i)
                                p = isl_printer_print_str(p, ", ");
                        p = isl_printer_print_int(p, kernel->block_dim[i]);
                }
        else
                p = isl_printer_print_str(p, "1");

        return p;
}

/* Set the arguments of the OpenCL kernel by printing a call to the OpenCL
 * clSetKernelArg() function for each kernel argument.
 */
static __isl_give isl_printer *opencl_set_kernel_arguments(
        __isl_take isl_printer *p, struct gpu_prog *prog,
        struct ppcg_kernel *kernel)
{
        int i, n, ro;
        unsigned nparam;
        isl_space *space;
        const char *type;
        int arg_index = 0;

        for (i = 0; i < prog->n_array; ++i) {
                isl_set *arr;
                int empty;

                space = isl_space_copy(prog->array[i].space);
                arr = isl_union_set_extract_set(kernel->arrays, space);
                empty = isl_set_plain_is_empty(arr);
                isl_set_free(arr);
                if (empty)
                        continue;
                ro = gpu_array_is_read_only_scalar(&prog->array[i]);
                opencl_set_kernel_argument(p, kernel->id, prog->array[i].name,
                        arg_index, ro);
                arg_index++;
        }

        space = isl_union_set_get_space(kernel->arrays);
        nparam = isl_space_dim(space, isl_dim_param);
        for (i = 0; i < nparam; ++i) {
                const char *name;

                name = isl_space_get_dim_name(space, isl_dim_param, i);
                opencl_set_kernel_argument(p, kernel->id, name, arg_index, 1);
                arg_index++;
        }
        isl_space_free(space);

        n = isl_space_dim(kernel->space, isl_dim_set);
        for (i = 0; i < n; ++i) {
                const char *name;
                isl_id *id;

                name = isl_space_get_dim_name(kernel->space, isl_dim_set, i);
                opencl_set_kernel_argument(p, kernel->id, name, arg_index, 1);
                arg_index++;
        }

        return p;
}

/* Print the arguments to a kernel declaration or call.  If "types" is set,
 * then print a declaration (including the types of the arguments).
 *
 * The arguments are printed in the following order
 * - the arrays accessed by the kernel
 * - the parameters
 * - the host loop iterators
 */
static __isl_give isl_printer *opencl_print_kernel_arguments(
        __isl_take isl_printer *p, struct gpu_prog *prog,
        struct ppcg_kernel *kernel, int types)
{
        int i, n;
        int first = 1;
        unsigned nparam;
        isl_space *space;
        const char *type;

        for (i = 0; i < prog->n_array; ++i) {
                isl_set *arr;
                int empty;

                space = isl_space_copy(prog->array[i].space);
                arr = isl_union_set_extract_set(kernel->arrays, space);
                empty = isl_set_plain_is_empty(arr);
                isl_set_free(arr);
                if (empty)
                        continue;

                if (!first)
                        p = isl_printer_print_str(p, ", ");

                if (types)
                        p = gpu_array_info_print_declaration_argument(p,
                                &prog->array[i], "__global");
                else
                        p = gpu_array_info_print_call_argument(p,
                                &prog->array[i]);

                first = 0;
        }

        space = isl_union_set_get_space(kernel->arrays);
        nparam = isl_space_dim(space, isl_dim_param);
        for (i = 0; i < nparam; ++i) {
                const char *name;

                name = isl_space_get_dim_name(space, isl_dim_param, i);

                if (!first)
                        p = isl_printer_print_str(p, ", ");
                if (types)
                        p = isl_printer_print_str(p, "int ");
                p = isl_printer_print_str(p, name);

                first = 0;
        }
        isl_space_free(space);

        n = isl_space_dim(kernel->space, isl_dim_set);
        type = isl_options_get_ast_iterator_type(prog->ctx);
        for (i = 0; i < n; ++i) {
                const char *name;
                isl_id *id;

                if (!first)
                        p = isl_printer_print_str(p, ", ");
                name = isl_space_get_dim_name(kernel->space, isl_dim_set, i);
                if (types) {
                        p = isl_printer_print_str(p, type);
                        p = isl_printer_print_str(p, " ");
                }
                p = isl_printer_print_str(p, name);

                first = 0;
        }

        return p;
}

/* Print the header of the given kernel.
 */
static __isl_give isl_printer *opencl_print_kernel_header(
        __isl_take isl_printer *p, struct gpu_prog *prog,
        struct ppcg_kernel *kernel)
{
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "__kernel void kernel");
        p = isl_printer_print_int(p, kernel->id);
        p = isl_printer_print_str(p, "(");
        p = opencl_print_kernel_arguments(p, prog, kernel, 1);
        p = isl_printer_print_str(p, ")");
        p = isl_printer_end_line(p);

        return p;
}

/* Unlike the equivalent function in the CUDA backend which prints iterators
 * in reverse order to promote coalescing, this function does not print
 * iterators in reverse order.  The OpenCL backend currently does not take
 * into account any coalescing considerations.
 */
static __isl_give isl_printer *opencl_print_kernel_iterators(
        __isl_take isl_printer *p, struct ppcg_kernel *kernel)
{
        int i, n_grid;
        isl_ctx *ctx = isl_ast_node_get_ctx(kernel->tree);
        const char *type;

        type = isl_options_get_ast_iterator_type(ctx);

        n_grid = isl_multi_pw_aff_dim(kernel->grid_size, isl_dim_set);
        if (n_grid > 0) {
                p = isl_printer_start_line(p);
                p = isl_printer_print_str(p, type);
                p = isl_printer_print_str(p, " ");
                for (i = 0; i < n_grid; ++i) {
                        if (i)
                                p = isl_printer_print_str(p, ", ");
                        p = isl_printer_print_str(p, "b");
                        p = isl_printer_print_int(p, i);
                        p = isl_printer_print_str(p, " = get_group_id(");
                        p = isl_printer_print_int(p, i);
                        p = isl_printer_print_str(p, ")");
                }
                p = isl_printer_print_str(p, ";");
                p = isl_printer_end_line(p);
        }

        if (kernel->n_block > 0) {
                p = isl_printer_start_line(p);
                p = isl_printer_print_str(p, type);
                p = isl_printer_print_str(p, " ");
                for (i = 0; i < kernel->n_block; ++i) {
                        if (i)
                                p = isl_printer_print_str(p, ", ");
                        p = isl_printer_print_str(p, "t");
                        p = isl_printer_print_int(p, i);
                        p = isl_printer_print_str(p, " = get_local_id(");
                        p = isl_printer_print_int(p, i);
                        p = isl_printer_print_str(p, ")");
                }
                p = isl_printer_print_str(p, ";");
                p = isl_printer_end_line(p);
        }

        return p;
}

static __isl_give isl_printer *opencl_print_kernel_var(
        __isl_take isl_printer *p, struct ppcg_kernel_var *var)
{
        int j;
        isl_val *v;

        p = isl_printer_start_line(p);
        if (var->type == ppcg_access_shared)
                p = isl_printer_print_str(p, "__local ");
        p = isl_printer_print_str(p, var->array->type);
        p = isl_printer_print_str(p, " ");
        p = isl_printer_print_str(p, var->name);
        for (j = 0; j < var->array->n_index; ++j) {
                p = isl_printer_print_str(p, "[");
                v = isl_vec_get_element_val(var->size, j);
                p = isl_printer_print_val(p, v);
                p = isl_printer_print_str(p, "]");
                isl_val_free(v);
        }
        p = isl_printer_print_str(p, ";");
        p = isl_printer_end_line(p);

        return p;
}

static __isl_give isl_printer *opencl_print_kernel_vars(
                __isl_take isl_printer *p, struct ppcg_kernel *kernel)
{
        int i;

        for (i = 0; i < kernel->n_var; ++i)
                p = opencl_print_kernel_var(p, &kernel->var[i]);

        return p;
}

/* Print a call to barrier() which is a sync statement.
 * All work-items in a work-group executing the kernel on a processor must
 * execute the barrier() function before any are allowed to continue execution
 * beyond the barrier.
 * The flag CLK_LOCAL_MEM_FENCE makes the barrier function either flush any
 * variables stored in local memory or queue a memory fence to ensure correct
 * ordering of memory operations to local memory.
 * The flag CLK_GLOBAL_MEM_FENCE makes the barrier function queue a memory
 * fence to ensure correct ordering of memory operations to global memory.
 */
static __isl_give isl_printer *opencl_print_sync(__isl_take isl_printer *p,
        struct ppcg_kernel_stmt *stmt)
{
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p,
                "barrier(CLK_LOCAL_MEM_FENCE | CLK_GLOBAL_MEM_FENCE);");
        p = isl_printer_end_line(p);

        return p;
}

/* This function is called for each user statement in the AST,
 * i.e., for each kernel body statement, copy statement or sync statement.
 */
static __isl_give isl_printer *opencl_print_kernel_stmt(
        __isl_take isl_printer *p,
        __isl_take isl_ast_print_options *print_options,
        __isl_keep isl_ast_node *node, void *user)
{
        isl_id *id;
        struct ppcg_kernel_stmt *stmt;

        id = isl_ast_node_get_annotation(node);
        stmt = isl_id_get_user(id);
        isl_id_free(id);

        isl_ast_print_options_free(print_options);

        switch (stmt->type) {
        case ppcg_kernel_copy:
                return ppcg_kernel_print_copy(p, stmt);
        case ppcg_kernel_sync:
                return opencl_print_sync(p, stmt);
        case ppcg_kernel_domain:
                return ppcg_kernel_print_domain(p, stmt);
        }

        return p;
}

/* Return true if there is a double array in prog->array or
 * if any of the types in prog->scop involve any doubles.
 * To check the latter condition, we simply search for the string "double"
 * in the type definitions, which may result in false positives.
 */
static __isl_give int any_double_elements(struct gpu_prog *prog)
{
        int i;

        for (i = 0; i < prog->n_array; ++i)
                if (strcmp(prog->array[i].type, "double") == 0)
                        return 1;

        for (i = 0; i < prog->scop->pet->n_type; ++i) {
                struct pet_type *type = prog->scop->pet->types[i];

                if (strstr(type->definition, "double"))
                        return 1;
        }

        return 0;
}

/* Prints a #pragma to enable support for double floating-point
 * precision.  OpenCL 1.0 adds support for double precision floating-point as
 * an optional extension. An application that wants to use double will need to
 * include the #pragma OPENCL EXTENSION cl_khr_fp64 : enable directive before
 * any double precision data type is declared in the kernel code.
 */
static __isl_give isl_printer *opencl_enable_double_support(
        __isl_take isl_printer *p)
{
        int i;

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "#pragma OPENCL EXTENSION cl_khr_fp64 :"
                " enable");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_end_line(p);

        return p;
}

static __isl_give isl_printer *opencl_print_kernel(struct gpu_prog *prog,
        struct ppcg_kernel *kernel, __isl_take isl_printer *p)
{
        isl_ctx *ctx = isl_ast_node_get_ctx(kernel->tree);
        isl_ast_print_options *print_options;

        print_options = isl_ast_print_options_alloc(ctx);
        print_options = isl_ast_print_options_set_print_user(print_options,
                                &opencl_print_kernel_stmt, NULL);

        p = isl_printer_set_output_format(p, ISL_FORMAT_C);
        p = opencl_print_kernel_header(p, prog, kernel);
        p = isl_printer_print_str(p, "{");
        p = isl_printer_end_line(p);
        p = isl_printer_indent(p, 4);
        p = opencl_print_kernel_iterators(p, kernel);
        p = opencl_print_kernel_vars(p, kernel);
        p = isl_printer_end_line(p);
        p = gpu_print_macros(p, kernel->tree);
        p = isl_ast_node_print(kernel->tree, p, print_options);
        p = isl_printer_indent(p, -4);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "}");
        p = isl_printer_end_line(p);

        return p;
}

struct print_host_user_data_opencl {
        struct opencl_info *opencl;
        struct gpu_prog *prog;
};

/* This function prints the i'th block size multiplied by the i'th grid size,
 * where i (a parameter to this function) is one of the possible dimensions of
 * grid sizes and block sizes.
 * If the dimension of block sizes is not equal to the dimension of grid sizes
 * the output is calculated as follows:
 *
 * Suppose that:
 * block_sizes[dim1] is the list of blocks sizes and it contains dim1 elements.
 * grid_sizes[dim2] is the list of grid sizes and it contains dim2 elements.
 *
 * The output is:
 * If (i > dim2) then the output is block_sizes[i]
 * If (i > dim1) then the output is grid_sizes[i]
 */
static __isl_give isl_printer *opencl_print_total_number_of_work_items_for_dim(
        __isl_take isl_printer *p, struct ppcg_kernel *kernel, int i)
{
        int grid_dim, block_dim;

        grid_dim = isl_multi_pw_aff_dim(kernel->grid_size, isl_dim_set);
        block_dim = kernel->n_block;

        isl_pw_aff *bound_grid;

        if (i < min(grid_dim, block_dim)) {
                bound_grid = isl_multi_pw_aff_get_pw_aff(kernel->grid_size, i);
                p = isl_printer_print_str(p, "(");
                p = isl_printer_print_pw_aff(p, bound_grid);
                p = isl_printer_print_str(p, ") * ");
                p = isl_printer_print_int(p, kernel->block_dim[i]);
                isl_pw_aff_free(bound_grid);
        } else if (i >= grid_dim)
                p = isl_printer_print_int(p, kernel->block_dim[i]);
        else {
                bound_grid = isl_multi_pw_aff_get_pw_aff(kernel->grid_size, i);
                p = isl_printer_print_pw_aff(p, bound_grid);
                isl_pw_aff_free(bound_grid);
        }

        return p;
}

/* Print a list that represents the total number of work items.  The list is
 * constructed by performing an element-wise multiplication of the block sizes
 * and the grid sizes.  To explain how the list is constructed, suppose that:
 * block_sizes[dim1] is the list of blocks sizes and it contains dim1 elements.
 * grid_sizes[dim2] is the list of grid sizes and it contains dim2 elements.
 *
 * The output of this function is constructed as follows:
 * If (dim1 > dim2) then the output is the following list:
 * grid_sizes[0]*block_sizes[0], ..., grid_sizes[dim2-1]*block_sizes[dim2-1],
 * block_sizes[dim2], ..., block_sizes[dim1-2], block_sizes[dim1-1].
 *
 * If (dim2 > dim1) then the output is the following list:
 * grid_sizes[0]*block_sizes[0], ..., grid_sizes[dim1-1] * block_sizes[dim1-1],
 * grid_sizes[dim1], grid_sizes[dim2-2], grid_sizes[dim2-1].
 *
 * To calculate the total number of work items out of the list constructed by
 * this function, the user should multiply the elements of the list.
 */
static __isl_give isl_printer *opencl_print_total_number_of_work_items_as_list(
        __isl_take isl_printer *p, struct ppcg_kernel *kernel)
{
        int i;
        int grid_dim, block_dim;

        grid_dim = isl_multi_pw_aff_dim(kernel->grid_size, isl_dim_set);
        block_dim = kernel->n_block;

        if ((grid_dim <= 0) || (block_dim <= 0)) {
                p = isl_printer_print_str(p, "1");
                return p;
        }

        for (i = 0; i <= max(grid_dim, block_dim) - 1; i++) {
                if (i > 0)
                        p = isl_printer_print_str(p, ", ");

                p = opencl_print_total_number_of_work_items_for_dim(p,
                        kernel, i);
        }

        return p;
}

/* Print the user statement of the host code to "p".
 *
 * In particular, print a block of statements that defines the grid
 * and the work group and then launches the kernel.
 *
 * A grid is composed of many work groups (blocks), each work group holds
 * many work-items (threads).
 *
 * global_work_size[kernel->n_block] represents the total number of work
 * items.  It points to an array of kernel->n_block unsigned
 * values that describe the total number of work-items that will execute
 * the kernel.  The total number of work-items is computed as:
 * global_work_size[0] *...* global_work_size[kernel->n_block - 1].
 *
 * The size of each work group (i.e. the number of work-items in each work
 * group) is described using block_size[kernel->n_block].  The total
 * number of work-items in a block (work-group) is computed as:
 * block_size[0] *... * block_size[kernel->n_block - 1].
 *
 * For more information check:
 * http://www.khronos.org/registry/cl/sdk/1.0/docs/man/xhtml/clEnqueueNDRangeKernel.html
 */
static __isl_give isl_printer *opencl_print_host_user(
        __isl_take isl_printer *p,
        __isl_take isl_ast_print_options *print_options,
        __isl_keep isl_ast_node *node, void *user)
{
        isl_id *id;
        struct ppcg_kernel *kernel;
        struct print_host_user_data_opencl *data;
        int i;

        id = isl_ast_node_get_annotation(node);
        kernel = isl_id_get_user(id);
        isl_id_free(id);

        data = (struct print_host_user_data_opencl *) user;

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "{");
        p = isl_printer_end_line(p);
        p = isl_printer_indent(p, 2);

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "size_t global_work_size[");

        if (kernel->n_block > 0)
                p = isl_printer_print_int(p, kernel->n_block);
        else
                p = isl_printer_print_int(p, 1);

        p = isl_printer_print_str(p, "] = {");
        p = opencl_print_total_number_of_work_items_as_list(p, kernel);
        p = isl_printer_print_str(p, "};");
        p = isl_printer_end_line(p);

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "size_t block_size[");

        if (kernel->n_block > 0)
                p = isl_printer_print_int(p, kernel->n_block);
        else
                p = isl_printer_print_int(p, 1);

        p = isl_printer_print_str(p, "] = {");
        p = opencl_print_block_sizes(p, kernel);
        p = isl_printer_print_str(p, "};");
        p = isl_printer_end_line(p);

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "cl_kernel kernel");
        p = isl_printer_print_int(p, kernel->id);
        p = isl_printer_print_str(p, " = clCreateKernel(program, \"kernel");
        p = isl_printer_print_int(p, kernel->id);
        p = isl_printer_print_str(p, "\", &err);");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn(err);");
        p = isl_printer_end_line(p);

        opencl_set_kernel_arguments(p, data->prog, kernel);

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn(clEnqueueNDRangeKernel"
                "(queue, kernel");
        p = isl_printer_print_int(p, kernel->id);
        p = isl_printer_print_str(p, ", ");
        if (kernel->n_block > 0)
                p = isl_printer_print_int(p, kernel->n_block);
        else
                p = isl_printer_print_int(p, 1);

        p = isl_printer_print_str(p, ", NULL, global_work_size, "
                                        "block_size, "
                                        "0, NULL, NULL));");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn("
                                        "clReleaseKernel(kernel");
        p = isl_printer_print_int(p, kernel->id);
        p = isl_printer_print_str(p, "));");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "clFinish(queue);");
        p = isl_printer_end_line(p);
        p = isl_printer_indent(p, -2);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "}");
        p = isl_printer_end_line(p);

        p = isl_printer_start_line(p);
        p = isl_printer_end_line(p);

        data->opencl->kprinter = opencl_print_kernel(data->prog, kernel,
                                                data->opencl->kprinter);

        isl_ast_print_options_free(print_options);

        return p;
}

static __isl_give isl_printer *opencl_print_host_code(
        __isl_take isl_printer *p, struct gpu_prog *prog,
        __isl_keep isl_ast_node *tree, struct opencl_info *opencl)
{
        isl_ast_print_options *print_options;
        isl_ctx *ctx = isl_ast_node_get_ctx(tree);
        struct print_host_user_data_opencl data = { opencl, prog };

        print_options = isl_ast_print_options_alloc(ctx);
        print_options = isl_ast_print_options_set_print_user(print_options,
                                &opencl_print_host_user, &data);

        p = gpu_print_macros(p, tree);
        p = isl_ast_node_print(tree, p, print_options);

        return p;
}

/* Copy "array" back from the GPU to the host.
 */
static __isl_give isl_printer *copy_array_from_device(__isl_take isl_printer *p,
        void *user)
{
        struct gpu_array_info *array = user;

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn("
                                        "clEnqueueReadBuffer(queue,"
                                        " dev_");
        p = isl_printer_print_str(p, array->name);
        p = isl_printer_print_str(p, ", CL_TRUE, 0, ");
        p = gpu_array_info_print_size(p, array);

        if (gpu_array_is_scalar(array))
                p = isl_printer_print_str(p, ", &");
        else
                p = isl_printer_print_str(p, ", ");
        p = isl_printer_print_str(p, array->name);
        p = isl_printer_print_str(p, ", 0, NULL, NULL));");
        p = isl_printer_end_line(p);

        return p;
}

/* Copy copy_out arrays back from the GPU to the host.
 *
 * Only perform the copying for arrays with strictly positive size.
 */
static __isl_give isl_printer *opencl_copy_arrays_from_device(
        __isl_take isl_printer *p, struct gpu_prog *prog)
{
        int i;
        isl_union_set *copy_out;
        copy_out = isl_union_set_copy(prog->copy_out);

        for (i = 0; i < prog->n_array; ++i) {
                struct gpu_array_info *array = &prog->array[i];
                isl_space *space;
                isl_set *copy_out_i;
                isl_set *guard;
                int empty;

                space = isl_space_copy(array->space);
                copy_out_i = isl_union_set_extract_set(copy_out, space);
                empty = isl_set_plain_is_empty(copy_out_i);
                isl_set_free(copy_out_i);
                if (empty)
                        continue;

                guard = gpu_array_positive_size_guard(array);
                p = ppcg_print_guarded(p, guard, isl_set_copy(prog->context),
                                            &copy_array_from_device, array);
        }

        isl_union_set_free(copy_out);
        p = isl_printer_start_line(p);
        p = isl_printer_end_line(p);
        return p;
}

/* Create an OpenCL device, context, command queue and build the kernel.
 * input is the name of the input file provided to ppcg.
 */
static __isl_give isl_printer *opencl_setup(__isl_take isl_printer *p,
        const char *input, struct opencl_info *info)
{
        int len;

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "cl_device_id device;");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "cl_context context;");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "cl_program program;");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "cl_command_queue queue;");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "cl_int err;");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "device = opencl_create_device(");
        p = isl_printer_print_int(p, info->options->opencl_use_gpu);
        p = isl_printer_print_str(p, ");");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "context = clCreateContext(NULL, 1, "
                "&device, NULL, NULL, &err);");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn(err);");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "queue = clCreateCommandQueue"
                                        "(context, device, 0, &err);");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn(err);");
        p = isl_printer_end_line(p);

        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "program = opencl_build_program("
                                        "context, device, \"");
        p = isl_printer_print_str(p, info->kernel_c_name);
        p = isl_printer_print_str(p, "\", \"");

        if (info->options->opencl_compiler_options)
                p = isl_printer_print_str(p,
                                        info->options->opencl_compiler_options);

        p = isl_printer_print_str(p, "\");");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_end_line(p);

        return p;
}

static __isl_give isl_printer *opencl_release_cl_objects(
        __isl_take isl_printer *p, struct opencl_info *info)
{
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn(clReleaseCommandQueue"
                                        "(queue));");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn(clReleaseProgram"
                                        "(program));");
        p = isl_printer_end_line(p);
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn(clReleaseContext"
                                        "(context));");
        p = isl_printer_end_line(p);

        return p;
}

/* Free the device array corresponding to "array"
 */
static __isl_give isl_printer *release_device_array(__isl_take isl_printer *p,
        struct gpu_array_info *array)
{
        p = isl_printer_start_line(p);
        p = isl_printer_print_str(p, "openclCheckReturn("
                                        "clReleaseMemObject(dev_");
        p = isl_printer_print_str(p, array->name);
        p = isl_printer_print_str(p, "));");
        p = isl_printer_end_line(p);

        return p;
}

/* Free the device arrays.
 */
static __isl_give isl_printer *opencl_release_device_arrays(
        __isl_take isl_printer *p, struct gpu_prog *prog)
{
        int i, j;

        for (i = 0; i < prog->n_array; ++i) {
                struct gpu_array_info *array = &prog->array[i];
                if (gpu_array_is_read_only_scalar(array))
                        continue;

                p = release_device_array(p, array);
        }
        return p;
}

/* Given a gpu_prog "prog" and the corresponding transformed AST
 * "tree", print the entire OpenCL code to "p".
 */
static __isl_give isl_printer *print_opencl(__isl_take isl_printer *p,
        struct gpu_prog *prog, __isl_keep isl_ast_node *tree,
        struct gpu_types *types, void *user)
{
        struct opencl_info *opencl = user;

        opencl->kprinter = isl_printer_set_output_format(opencl->kprinter,
                                                        ISL_FORMAT_C);
        if (any_double_elements(prog))
                opencl->kprinter = opencl_enable_double_support(
                                                        opencl->kprinter);
        opencl->kprinter = gpu_print_types(opencl->kprinter, types, prog);

        if (!opencl->kprinter)
                return isl_printer_free(p);

        p = ppcg_start_block(p);

        p = opencl_print_host_macros(p);

        p = opencl_declare_device_arrays(p, prog);
        p = opencl_setup(p, opencl->input, opencl);
        p = opencl_allocate_device_arrays(p, prog);

        p = opencl_print_host_code(p, prog, tree, opencl);

        p = opencl_copy_arrays_from_device(p, prog);
        p = opencl_release_device_arrays(p, prog);
        p = opencl_release_cl_objects(p, opencl);

        p = ppcg_end_block(p);

        return p;
}

/* Transform the code in the file called "input" by replacing
 * all scops by corresponding OpenCL code.
 * The host code is written to "output" or a name derived from
 * "input" if "output" is NULL.
 * The kernel code is placed in separate files with names
 * derived from "output" or "input".
 *
 * We let generate_gpu do all the hard work and then let it call
 * us back for printing the AST in print_cuda.
 *
 * To prepare for this printing, we first open the output files
 * and we close them after generate_gpu has finished.
 */
int generate_opencl(isl_ctx *ctx, struct ppcg_options *options,
        const char *input, const char *output)
{
        struct opencl_info opencl = { options, input, output };
        int r;

        opencl.kprinter = isl_printer_to_str(ctx);
        r = opencl_open_files(&opencl);

        if (r >= 0)
                r = generate_gpu(ctx, input, opencl.host_c, options,
                                &print_opencl, &opencl);

        opencl_close_files(&opencl);
        isl_printer_free(opencl.kprinter);

        return r;
}