ppcg_kernel_requires_array_argument: check if kernel acceses global memory

[ppcg.git] / ppcg.c

/*
 * Copyright 2011      INRIA Saclay
 * Copyright 2013      Ecole Normale Superieure
 * Copyright 2015      Sven Verdoolaege
 *
 * Use of this software is governed by the MIT license
 *
 * Written by Sven Verdoolaege, INRIA Saclay - Ile-de-France,
 * Parc Club Orsay Universite, ZAC des vignes, 4 rue Jacques Monod,
 * 91893 Orsay, France
 * and Ecole Normale Superieure, 45 rue d'Ulm, 75230 Paris, France
 */

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <isl/ctx.h>
#include <isl/flow.h>
#include <isl/options.h>
#include <isl/schedule.h>
#include <isl/ast_build.h>
#include <isl/schedule.h>
#include <pet.h>
#include "ppcg.h"
#include "ppcg_options.h"
#include "cuda.h"
#include "opencl.h"
#include "cpu.h"

struct options {
        struct isl_options *isl;
        struct pet_options *pet;
        struct ppcg_options *ppcg;
        char *input;
        char *output;
};

const char *ppcg_version(void);
static void print_version(void)
{
        printf("%s", ppcg_version());
}

ISL_ARGS_START(struct options, options_args)
ISL_ARG_CHILD(struct options, isl, "isl", &isl_options_args, "isl options")
ISL_ARG_CHILD(struct options, pet, "pet", &pet_options_args, "pet options")
ISL_ARG_CHILD(struct options, ppcg, NULL, &ppcg_options_args, "ppcg options")
ISL_ARG_STR(struct options, output, 'o', NULL,
        "filename", NULL, "output filename (c and opencl targets)")
ISL_ARG_ARG(struct options, input, "input", NULL)
ISL_ARG_VERSION(print_version)
ISL_ARGS_END

ISL_ARG_DEF(options, struct options, options_args)

/* Return a pointer to the final path component of "filename" or
 * to "filename" itself if it does not contain any components.
 */
const char *ppcg_base_name(const char *filename)
{
        const char *base;

        base = strrchr(filename, '/');
        if (base)
                return ++base;
        else
                return filename;
}

/* Copy the base name of "input" to "name" and return its length.
 * "name" is not NULL terminated.
 *
 * In particular, remove all leading directory components and
 * the final extension, if any.
 */
int ppcg_extract_base_name(char *name, const char *input)
{
        const char *base;
        const char *ext;
        int len;

        base = ppcg_base_name(input);
        ext = strrchr(base, '.');
        len = ext ? ext - base : strlen(base);

        memcpy(name, base, len);

        return len;
}

/* Does "scop" refer to any arrays that are declared, but not
 * exposed to the code after the scop?
 */
int ppcg_scop_any_hidden_declarations(struct ppcg_scop *scop)
{
        int i;

        if (!scop)
                return 0;

        for (i = 0; i < scop->pet->n_array; ++i)
                if (scop->pet->arrays[i]->declared &&
                    !scop->pet->arrays[i]->exposed)
                        return 1;

        return 0;
}

/* Collect all variable names that are in use in "scop".
 * In particular, collect all parameters in the context and
 * all the array names.
 * Store these names in an isl_id_to_ast_expr by mapping
 * them to a dummy value (0).
 */
static __isl_give isl_id_to_ast_expr *collect_names(struct pet_scop *scop)
{
        int i, n;
        isl_ctx *ctx;
        isl_ast_expr *zero;
        isl_id_to_ast_expr *names;

        ctx = isl_set_get_ctx(scop->context);

        n = isl_set_dim(scop->context, isl_dim_param);

        names = isl_id_to_ast_expr_alloc(ctx, n + scop->n_array);
        zero = isl_ast_expr_from_val(isl_val_zero(ctx));

        for (i = 0; i < n; ++i) {
                isl_id *id;

                id = isl_set_get_dim_id(scop->context, isl_dim_param, i);
                names = isl_id_to_ast_expr_set(names,
                                                id, isl_ast_expr_copy(zero));
        }

        for (i = 0; i < scop->n_array; ++i) {
                struct pet_array *array = scop->arrays[i];
                isl_id *id;

                id = isl_set_get_tuple_id(array->extent);
                names = isl_id_to_ast_expr_set(names,
                                                id, isl_ast_expr_copy(zero));
        }

        isl_ast_expr_free(zero);

        return names;
}

/* Return an isl_id called "prefix%d", with "%d" set to "i".
 * If an isl_id with such a name already appears among the variable names
 * of "scop", then adjust the name to "prefix%d_%d".
 */
static __isl_give isl_id *generate_name(struct ppcg_scop *scop,
        const char *prefix, int i)
{
        int j;
        char name[16];
        isl_ctx *ctx;
        isl_id *id;
        int has_name;

        ctx = isl_set_get_ctx(scop->context);
        snprintf(name, sizeof(name), "%s%d", prefix, i);
        id = isl_id_alloc(ctx, name, NULL);

        j = 0;
        while ((has_name = isl_id_to_ast_expr_has(scop->names, id)) == 1) {
                isl_id_free(id);
                snprintf(name, sizeof(name), "%s%d_%d", prefix, i, j++);
                id = isl_id_alloc(ctx, name, NULL);
        }

        return has_name < 0 ? isl_id_free(id) : id;
}

/* Return a list of "n" isl_ids of the form "prefix%d".
 * If an isl_id with such a name already appears among the variable names
 * of "scop", then adjust the name to "prefix%d_%d".
 */
__isl_give isl_id_list *ppcg_scop_generate_names(struct ppcg_scop *scop,
        int n, const char *prefix)
{
        int i;
        char name[10];
        isl_ctx *ctx;
        isl_id_list *names;

        ctx = isl_set_get_ctx(scop->context);
        names = isl_id_list_alloc(ctx, n);
        for (i = 0; i < n; ++i) {
                isl_id *id;

                id = generate_name(scop, prefix, i);
                names = isl_id_list_add(names, id);
        }

        return names;
}

/* Is "stmt" not a kill statement?
 */
static int is_not_kill(struct pet_stmt *stmt)
{
        return !pet_stmt_is_kill(stmt);
}

/* Collect the iteration domains of the statements in "scop" that
 * satisfy "pred".
 */
static __isl_give isl_union_set *collect_domains(struct pet_scop *scop,
        int (*pred)(struct pet_stmt *stmt))
{
        int i;
        isl_set *domain_i;
        isl_union_set *domain;

        if (!scop)
                return NULL;

        domain = isl_union_set_empty(isl_set_get_space(scop->context));

        for (i = 0; i < scop->n_stmt; ++i) {
                struct pet_stmt *stmt = scop->stmts[i];

                if (!pred(stmt))
                        continue;

                if (stmt->n_arg > 0)
                        isl_die(isl_union_set_get_ctx(domain),
                                isl_error_unsupported,
                                "data dependent conditions not supported",
                                return isl_union_set_free(domain));

                domain_i = isl_set_copy(scop->stmts[i]->domain);
                domain = isl_union_set_add_set(domain, domain_i);
        }

        return domain;
}

/* Collect the iteration domains of the statements in "scop",
 * skipping kill statements.
 */
static __isl_give isl_union_set *collect_non_kill_domains(struct pet_scop *scop)
{
        return collect_domains(scop, &is_not_kill);
}

/* This function is used as a callback to pet_expr_foreach_call_expr
 * to detect if there is any call expression in the input expression.
 * Assign the value 1 to the integer that "user" points to and
 * abort the search since we have found what we were looking for.
 */
static int set_has_call(__isl_keep pet_expr *expr, void *user)
{
        int *has_call = user;

        *has_call = 1;

        return -1;
}

/* Does "expr" contain any call expressions?
 */
static int expr_has_call(__isl_keep pet_expr *expr)
{
        int has_call = 0;

        if (pet_expr_foreach_call_expr(expr, &set_has_call, &has_call) < 0 &&
            !has_call)
                return -1;

        return has_call;
}

/* This function is a callback for pet_tree_foreach_expr.
 * If "expr" contains any call (sub)expressions, then set *has_call
 * and abort the search.
 */
static int check_call(__isl_keep pet_expr *expr, void *user)
{
        int *has_call = user;

        if (expr_has_call(expr))
                *has_call = 1;

        return *has_call ? -1 : 0;
}

/* Does "stmt" contain any call expressions?
 */
static int has_call(struct pet_stmt *stmt)
{
        int has_call = 0;

        if (pet_tree_foreach_expr(stmt->body, &check_call, &has_call) < 0 &&
            !has_call)
                return -1;

        return has_call;
}

/* Collect the iteration domains of the statements in "scop"
 * that contain a call expression.
 */
static __isl_give isl_union_set *collect_call_domains(struct pet_scop *scop)
{
        return collect_domains(scop, &has_call);
}

/* Given a union of "tagged" access relations of the form
 *
 *      [S_i[...] -> R_j[]] -> A_k[...]
 *
 * project out the "tags" (R_j[]).
 * That is, return a union of relations of the form
 *
 *      S_i[...] -> A_k[...]
 */
static __isl_give isl_union_map *project_out_tags(
        __isl_take isl_union_map *umap)
{
        return isl_union_map_domain_factor_domain(umap);
}

/* Construct a function from tagged iteration domains to the corresponding
 * untagged iteration domains with as range of the wrapped map in the domain
 * the reference tags that appear in any of the reads, writes or kills.
 * Store the result in ps->tagger.
 *
 * For example, if the statement with iteration space S[i,j]
 * contains two array references R_1[] and R_2[], then ps->tagger will contain
 *
 *      { [S[i,j] -> R_1[]] -> S[i,j]; [S[i,j] -> R_2[]] -> S[i,j] }
 */
static void compute_tagger(struct ppcg_scop *ps)
{
        isl_union_map *tagged;
        isl_union_pw_multi_aff *tagger;

        tagged = isl_union_map_copy(ps->tagged_reads);
        tagged = isl_union_map_union(tagged,
                                isl_union_map_copy(ps->tagged_may_writes));
        tagged = isl_union_map_union(tagged,
                                isl_union_map_copy(ps->tagged_must_kills));
        tagged = isl_union_map_universe(tagged);
        tagged = isl_union_set_unwrap(isl_union_map_domain(tagged));

        tagger = isl_union_map_domain_map_union_pw_multi_aff(tagged);

        ps->tagger = tagger;
}

/* Compute the live out accesses, i.e., the writes that are
 * potentially not killed by any kills or any other writes, and
 * store them in ps->live_out.
 *
 * We compute the "dependence" of any "kill" (an explicit kill
 * or a must write) on any may write.
 * The may writes with a "depending" kill are definitely killed.
 * The remaining may writes can potentially be live out.
 */
static void compute_live_out(struct ppcg_scop *ps)
{
        isl_union_pw_multi_aff *tagger;
        isl_schedule *schedule;
        isl_union_map *kills;
        isl_union_map *exposed;
        isl_union_map *covering;
        isl_union_access_info *access;
        isl_union_flow *flow;

        tagger = isl_union_pw_multi_aff_copy(ps->tagger);
        schedule = isl_schedule_copy(ps->schedule);
        schedule = isl_schedule_pullback_union_pw_multi_aff(schedule, tagger);
        kills = isl_union_map_union(isl_union_map_copy(ps->tagged_must_writes),
                                    isl_union_map_copy(ps->tagged_must_kills));
        access = isl_union_access_info_from_sink(kills);
        access = isl_union_access_info_set_may_source(access,
                                isl_union_map_copy(ps->tagged_may_writes));
        access = isl_union_access_info_set_schedule(access, schedule);
        flow = isl_union_access_info_compute_flow(access);
        covering = isl_union_flow_get_may_dependence(flow);
        isl_union_flow_free(flow);
        exposed = isl_union_map_copy(ps->tagged_may_writes);
        exposed = isl_union_map_subtract_domain(exposed,
                                isl_union_map_domain(covering));
        ps->live_out = project_out_tags(exposed);
}

/* Compute the tagged flow dependences and the live_in accesses and store
 * the results in ps->tagged_dep_flow and ps->live_in.
 *
 * We allow both the must writes and the must kills to serve as
 * definite sources such that a subsequent read would not depend
 * on any earlier write.  The resulting flow dependences with
 * a must kill as source reflect possibly uninitialized reads.
 * No dependences need to be introduced to protect such reads
 * (other than those imposed by potential flows from may writes
 * that follow the kill).  We therefore remove those flow dependences.
 * This is also useful for the dead code elimination, which assumes
 * the flow sources are non-kill instances.
 */
static void compute_tagged_flow_dep_only(struct ppcg_scop *ps)
{
        isl_union_pw_multi_aff *tagger;
        isl_schedule *schedule;
        isl_union_map *live_in;
        isl_union_access_info *access;
        isl_union_flow *flow;
        isl_union_map *must_source;
        isl_union_map *kills;
        isl_union_map *tagged_flow;

        tagger = isl_union_pw_multi_aff_copy(ps->tagger);
        schedule = isl_schedule_copy(ps->schedule);
        schedule = isl_schedule_pullback_union_pw_multi_aff(schedule, tagger);
        kills = isl_union_map_copy(ps->tagged_must_kills);
        must_source = isl_union_map_copy(ps->tagged_must_writes);
        must_source = isl_union_map_union(must_source,
                                isl_union_map_copy(kills));
        access = isl_union_access_info_from_sink(
                                isl_union_map_copy(ps->tagged_reads));
        access = isl_union_access_info_set_must_source(access, must_source);
        access = isl_union_access_info_set_may_source(access,
                                isl_union_map_copy(ps->tagged_may_writes));
        access = isl_union_access_info_set_schedule(access, schedule);
        flow = isl_union_access_info_compute_flow(access);
        tagged_flow = isl_union_flow_get_may_dependence(flow);
        tagged_flow = isl_union_map_subtract_domain(tagged_flow,
                                isl_union_map_domain(kills));
        ps->tagged_dep_flow = tagged_flow;
        live_in = isl_union_flow_get_may_no_source(flow);
        ps->live_in = project_out_tags(live_in);
        isl_union_flow_free(flow);
}

/* Compute ps->dep_flow from ps->tagged_dep_flow
 * by projecting out the reference tags.
 */
static void derive_flow_dep_from_tagged_flow_dep(struct ppcg_scop *ps)
{
        ps->dep_flow = isl_union_map_copy(ps->tagged_dep_flow);
        ps->dep_flow = isl_union_map_factor_domain(ps->dep_flow);
}

/* Compute the flow dependences and the live_in accesses and store
 * the results in ps->dep_flow and ps->live_in.
 * A copy of the flow dependences, tagged with the reference tags
 * is stored in ps->tagged_dep_flow.
 *
 * We first compute ps->tagged_dep_flow, i.e., the tagged flow dependences
 * and then project out the tags.
 */
static void compute_tagged_flow_dep(struct ppcg_scop *ps)
{
        compute_tagged_flow_dep_only(ps);
        derive_flow_dep_from_tagged_flow_dep(ps);
}

/* Compute the order dependences that prevent the potential live ranges
 * from overlapping.
 * "before" contains all pairs of statement iterations where
 * the first is executed before the second according to the original schedule.
 *
 * In particular, construct a union of relations
 *
 *      [R[...] -> R_1[]] -> [W[...] -> R_2[]]
 *
 * where [R[...] -> R_1[]] is the range of one or more live ranges
 * (i.e., a read) and [W[...] -> R_2[]] is the domain of one or more
 * live ranges (i.e., a write).  Moreover, the read and the write
 * access the same memory element and the read occurs before the write
 * in the original schedule.
 * The scheduler allows some of these dependences to be violated, provided
 * the adjacent live ranges are all local (i.e., their domain and range
 * are mapped to the same point by the current schedule band).
 *
 * Note that if a live range is not local, then we need to make
 * sure it does not overlap with _any_ other live range, and not
 * just with the "previous" and/or the "next" live range.
 * We therefore add order dependences between reads and
 * _any_ later potential write.
 *
 * We also need to be careful about writes without a corresponding read.
 * They are already prevented from moving past non-local preceding
 * intervals, but we also need to prevent them from moving past non-local
 * following intervals.  We therefore also add order dependences from
 * potential writes that do not appear in any intervals
 * to all later potential writes.
 * Note that dead code elimination should have removed most of these
 * dead writes, but the dead code elimination may not remove all dead writes,
 * so we need to consider them to be safe.
 */
static void compute_order_dependences(struct ppcg_scop *ps,
        __isl_take isl_union_map *before)
{
        isl_union_map *reads;
        isl_union_map *shared_access;
        isl_union_set *matched;
        isl_union_map *unmatched;
        isl_union_set *domain;

        reads = isl_union_map_copy(ps->tagged_reads);
        matched = isl_union_map_domain(isl_union_map_copy(ps->tagged_dep_flow));
        unmatched = isl_union_map_copy(ps->tagged_may_writes);
        unmatched = isl_union_map_subtract_domain(unmatched, matched);
        reads = isl_union_map_union(reads, unmatched);
        shared_access = isl_union_map_copy(ps->tagged_may_writes);
        shared_access = isl_union_map_reverse(shared_access);
        shared_access = isl_union_map_apply_range(reads, shared_access);
        shared_access = isl_union_map_zip(shared_access);
        shared_access = isl_union_map_intersect_domain(shared_access,
                                                isl_union_map_wrap(before));
        domain = isl_union_map_domain(isl_union_map_copy(shared_access));
        shared_access = isl_union_map_zip(shared_access);
        ps->dep_order = isl_union_set_unwrap(domain);
        ps->tagged_dep_order = shared_access;
}

/* Compute those validity dependences of the program represented by "scop"
 * that should be unconditionally enforced even when live-range reordering
 * is used.
 * "before" contains all pairs of statement iterations where
 * the first is executed before the second according to the original schedule.
 *
 * In particular, compute the external false dependences
 * as well as order dependences between sources with the same sink.
 * The anti-dependences are already taken care of by the order dependences.
 * The external false dependences are only used to ensure that live-in and
 * live-out data is not overwritten by any writes inside the scop.
 *
 * In particular, the reads from live-in data need to precede any
 * later write to the same memory element.
 * As to live-out data, the last writes need to remain the last writes.
 * That is, any earlier write in the original schedule needs to precede
 * the last write to the same memory element in the computed schedule.
 * The possible last writes have been computed by compute_live_out.
 * They may include kills, but if the last access is a kill,
 * then the corresponding dependences will effectively be ignored
 * since we do not schedule any kill statements.
 *
 * Note that the set of live-in and live-out accesses may be
 * an overapproximation.  There may therefore be potential writes
 * before a live-in access and after a live-out access.
 *
 * In the presence of may-writes, there may be multiple live-ranges
 * with the same sink, accessing the same memory element.
 * The sources of these live-ranges need to be executed
 * in the same relative order as in the original program
 * since we do not know which of the may-writes will actually
 * perform a write.  Consider all sources that share a sink and
 * that may write to the same memory element and compute
 * the order dependences among them.
 */
static void compute_forced_dependences(struct ppcg_scop *ps,
        __isl_take isl_union_map *before)
{
        isl_union_map *shared_access;
        isl_union_map *exposed;
        isl_union_map *live_in;
        isl_union_map *sink_access;
        isl_union_map *shared_sink;
        isl_union_access_info *access;
        isl_union_flow *flow;
        isl_schedule *schedule;

        exposed = isl_union_map_copy(ps->live_out);

        exposed = isl_union_map_reverse(exposed);
        shared_access = isl_union_map_copy(ps->may_writes);
        shared_access = isl_union_map_apply_range(shared_access, exposed);

        ps->dep_forced = shared_access;

        live_in = isl_union_map_apply_range(isl_union_map_copy(ps->live_in),
                    isl_union_map_reverse(isl_union_map_copy(ps->may_writes)));

        ps->dep_forced = isl_union_map_union(ps->dep_forced, live_in);
        ps->dep_forced = isl_union_map_intersect(ps->dep_forced, before);

        schedule = isl_schedule_copy(ps->schedule);
        sink_access = isl_union_map_copy(ps->tagged_dep_flow);
        sink_access = isl_union_map_range_product(sink_access,
                                isl_union_map_copy(ps->tagged_may_writes));
        sink_access = isl_union_map_domain_factor_domain(sink_access);
        access = isl_union_access_info_from_sink(
                                isl_union_map_copy(sink_access));
        access = isl_union_access_info_set_may_source(access, sink_access);
        access = isl_union_access_info_set_schedule(access, schedule);
        flow = isl_union_access_info_compute_flow(access);
        shared_sink = isl_union_flow_get_may_dependence(flow);
        isl_union_flow_free(flow);
        ps->dep_forced = isl_union_map_union(ps->dep_forced, shared_sink);
}

/* Remove independence from the tagged flow dependences.
 * Since the user has guaranteed that source and sink of an independence
 * can be executed in any order, there cannot be a flow dependence
 * between them, so they can be removed from the set of flow dependences.
 * However, if the source of such a flow dependence is a must write,
 * then it may have killed other potential sources, which would have
 * to be recovered if we were to remove those flow dependences.
 * We therefore keep the flow dependences that originate in a must write,
 * even if it corresponds to a known independence.
 */
static void remove_independences_from_tagged_flow(struct ppcg_scop *ps)
{
        isl_union_map *tf;
        isl_union_set *indep;
        isl_union_set *mw;

        tf = isl_union_map_copy(ps->tagged_dep_flow);
        tf = isl_union_map_zip(tf);
        indep = isl_union_map_wrap(isl_union_map_copy(ps->independence));
        tf = isl_union_map_intersect_domain(tf, indep);
        tf = isl_union_map_zip(tf);
        mw = isl_union_map_domain(isl_union_map_copy(ps->tagged_must_writes));
        tf = isl_union_map_subtract_domain(tf, mw);
        ps->tagged_dep_flow = isl_union_map_subtract(ps->tagged_dep_flow, tf);
}

/* Compute the dependences of the program represented by "scop"
 * in case live range reordering is allowed.
 *
 * We compute the actual live ranges and the corresponding order
 * false dependences.
 *
 * The independences are removed from the flow dependences
 * (provided the source is not a must-write) as well as
 * from the external false dependences.
 */
static void compute_live_range_reordering_dependences(struct ppcg_scop *ps)
{
        isl_union_map *before;
        isl_union_map *schedule;

        schedule = isl_schedule_get_map(ps->schedule);
        before = isl_union_map_lex_lt_union_map(schedule,
                        isl_union_map_copy(schedule));

        compute_tagged_flow_dep_only(ps);
        remove_independences_from_tagged_flow(ps);
        derive_flow_dep_from_tagged_flow_dep(ps);
        compute_order_dependences(ps, isl_union_map_copy(before));
        before = isl_union_map_subtract(before,
                                        isl_union_map_copy(ps->independence));
        compute_forced_dependences(ps, before);
}

/* Compute the potential flow dependences and the potential live in
 * accesses.
 */
static void compute_flow_dep(struct ppcg_scop *ps)
{
        isl_union_access_info *access;
        isl_union_flow *flow;

        access = isl_union_access_info_from_sink(isl_union_map_copy(ps->reads));
        access = isl_union_access_info_set_must_source(access,
                                isl_union_map_copy(ps->must_writes));
        access = isl_union_access_info_set_may_source(access,
                                isl_union_map_copy(ps->may_writes));
        access = isl_union_access_info_set_schedule(access,
                                isl_schedule_copy(ps->schedule));
        flow = isl_union_access_info_compute_flow(access);

        ps->dep_flow = isl_union_flow_get_may_dependence(flow);
        ps->live_in = isl_union_flow_get_may_no_source(flow);
        isl_union_flow_free(flow);
}

/* Compute the dependences of the program represented by "scop".
 * Store the computed potential flow dependences
 * in scop->dep_flow and the reads with potentially no corresponding writes in
 * scop->live_in.
 * Store the potential live out accesses in scop->live_out.
 * Store the potential false (anti and output) dependences in scop->dep_false.
 *
 * If live range reordering is allowed, then we compute a separate
 * set of order dependences and a set of external false dependences
 * in compute_live_range_reordering_dependences.
 */
static void compute_dependences(struct ppcg_scop *scop)
{
        isl_union_map *may_source;
        isl_union_access_info *access;
        isl_union_flow *flow;

        if (!scop)
                return;

        compute_live_out(scop);

        if (scop->options->live_range_reordering)
                compute_live_range_reordering_dependences(scop);
        else if (scop->options->target != PPCG_TARGET_C)
                compute_tagged_flow_dep(scop);
        else
                compute_flow_dep(scop);

        may_source = isl_union_map_union(isl_union_map_copy(scop->may_writes),
                                        isl_union_map_copy(scop->reads));
        access = isl_union_access_info_from_sink(
                                isl_union_map_copy(scop->may_writes));
        access = isl_union_access_info_set_must_source(access,
                                isl_union_map_copy(scop->must_writes));
        access = isl_union_access_info_set_may_source(access, may_source);
        access = isl_union_access_info_set_schedule(access,
                                isl_schedule_copy(scop->schedule));
        flow = isl_union_access_info_compute_flow(access);

        scop->dep_false = isl_union_flow_get_may_dependence(flow);
        scop->dep_false = isl_union_map_coalesce(scop->dep_false);
        isl_union_flow_free(flow);
}

/* Eliminate dead code from ps->domain.
 *
 * In particular, intersect both ps->domain and the domain of
 * ps->schedule with the (parts of) iteration
 * domains that are needed to produce the output or for statement
 * iterations that call functions.
 * Also intersect the range of the dataflow dependences with
 * this domain such that the removed instances will no longer
 * be considered as targets of dataflow.
 *
 * We start with the iteration domains that call functions
 * and the set of iterations that last write to an array
 * (except those that are later killed).
 *
 * Then we add those statement iterations that produce
 * something needed by the "live" statements iterations.
 * We keep doing this until no more statement iterations can be added.
 * To ensure that the procedure terminates, we compute the affine
 * hull of the live iterations (bounded to the original iteration
 * domains) each time we have added extra iterations.
 */
static void eliminate_dead_code(struct ppcg_scop *ps)
{
        isl_union_set *live;
        isl_union_map *dep;
        isl_union_pw_multi_aff *tagger;

        live = isl_union_map_domain(isl_union_map_copy(ps->live_out));
        if (!isl_union_set_is_empty(ps->call)) {
                live = isl_union_set_union(live, isl_union_set_copy(ps->call));
                live = isl_union_set_coalesce(live);
        }

        dep = isl_union_map_copy(ps->dep_flow);
        dep = isl_union_map_reverse(dep);

        for (;;) {
                isl_union_set *extra;

                extra = isl_union_set_apply(isl_union_set_copy(live),
                                            isl_union_map_copy(dep));
                if (isl_union_set_is_subset(extra, live)) {
                        isl_union_set_free(extra);
                        break;
                }

                live = isl_union_set_union(live, extra);
                live = isl_union_set_affine_hull(live);
                live = isl_union_set_intersect(live,
                                            isl_union_set_copy(ps->domain));
        }

        isl_union_map_free(dep);

        ps->domain = isl_union_set_intersect(ps->domain,
                                                isl_union_set_copy(live));
        ps->schedule = isl_schedule_intersect_domain(ps->schedule,
                                                isl_union_set_copy(live));
        ps->dep_flow = isl_union_map_intersect_range(ps->dep_flow,
                                                isl_union_set_copy(live));
        tagger = isl_union_pw_multi_aff_copy(ps->tagger);
        live = isl_union_set_preimage_union_pw_multi_aff(live, tagger);
        ps->tagged_dep_flow = isl_union_map_intersect_range(ps->tagged_dep_flow,
                                                live);
}

/* Intersect "set" with the set described by "str", taking the NULL
 * string to represent the universal set.
 */
static __isl_give isl_set *set_intersect_str(__isl_take isl_set *set,
        const char *str)
{
        isl_ctx *ctx;
        isl_set *set2;

        if (!str)
                return set;

        ctx = isl_set_get_ctx(set);
        set2 = isl_set_read_from_str(ctx, str);
        set = isl_set_intersect(set, set2);

        return set;
}

static void *ppcg_scop_free(struct ppcg_scop *ps)
{
        if (!ps)
                return NULL;

        isl_set_free(ps->context);
        isl_union_set_free(ps->domain);
        isl_union_set_free(ps->call);
        isl_union_map_free(ps->tagged_reads);
        isl_union_map_free(ps->reads);
        isl_union_map_free(ps->live_in);
        isl_union_map_free(ps->tagged_may_writes);
        isl_union_map_free(ps->tagged_must_writes);
        isl_union_map_free(ps->may_writes);
        isl_union_map_free(ps->must_writes);
        isl_union_map_free(ps->live_out);
        isl_union_map_free(ps->tagged_must_kills);
        isl_union_map_free(ps->tagged_dep_flow);
        isl_union_map_free(ps->dep_flow);
        isl_union_map_free(ps->dep_false);
        isl_union_map_free(ps->dep_forced);
        isl_union_map_free(ps->tagged_dep_order);
        isl_union_map_free(ps->dep_order);
        isl_schedule_free(ps->schedule);
        isl_union_pw_multi_aff_free(ps->tagger);
        isl_union_map_free(ps->independence);
        isl_id_to_ast_expr_free(ps->names);

        free(ps);

        return NULL;
}

/* Extract a ppcg_scop from a pet_scop.
 *
 * The constructed ppcg_scop refers to elements from the pet_scop
 * so the pet_scop should not be freed before the ppcg_scop.
 */
static struct ppcg_scop *ppcg_scop_from_pet_scop(struct pet_scop *scop,
        struct ppcg_options *options)
{
        int i;
        isl_ctx *ctx;
        struct ppcg_scop *ps;

        if (!scop)
                return NULL;

        ctx = isl_set_get_ctx(scop->context);

        ps = isl_calloc_type(ctx, struct ppcg_scop);
        if (!ps)
                return NULL;

        ps->names = collect_names(scop);
        ps->options = options;
        ps->start = pet_loc_get_start(scop->loc);
        ps->end = pet_loc_get_end(scop->loc);
        ps->context = isl_set_copy(scop->context);
        ps->context = set_intersect_str(ps->context, options->ctx);
        if (options->non_negative_parameters) {
                isl_space *space = isl_set_get_space(ps->context);
                isl_set *nn = isl_set_nat_universe(space);
                ps->context = isl_set_intersect(ps->context, nn);
        }
        ps->domain = collect_non_kill_domains(scop);
        ps->call = collect_call_domains(scop);
        ps->tagged_reads = pet_scop_collect_tagged_may_reads(scop);
        ps->reads = pet_scop_collect_may_reads(scop);
        ps->tagged_may_writes = pet_scop_collect_tagged_may_writes(scop);
        ps->may_writes = pet_scop_collect_may_writes(scop);
        ps->tagged_must_writes = pet_scop_collect_tagged_must_writes(scop);
        ps->must_writes = pet_scop_collect_must_writes(scop);
        ps->tagged_must_kills = pet_scop_collect_tagged_must_kills(scop);
        ps->schedule = isl_schedule_copy(scop->schedule);
        ps->pet = scop;
        ps->independence = isl_union_map_empty(isl_set_get_space(ps->context));
        for (i = 0; i < scop->n_independence; ++i)
                ps->independence = isl_union_map_union(ps->independence,
                        isl_union_map_copy(scop->independences[i]->filter));

        compute_tagger(ps);
        compute_dependences(ps);
        eliminate_dead_code(ps);

        if (!ps->context || !ps->domain || !ps->call || !ps->reads ||
            !ps->may_writes || !ps->must_writes || !ps->tagged_must_kills ||
            !ps->schedule || !ps->independence || !ps->names)
                return ppcg_scop_free(ps);

        return ps;
}

/* Internal data structure for ppcg_transform.
 */
struct ppcg_transform_data {
        struct ppcg_options *options;
        __isl_give isl_printer *(*transform)(__isl_take isl_printer *p,
                struct ppcg_scop *scop, void *user);
        void *user;
};

/* Should we print the original code?
 * That is, does "scop" involve any data dependent conditions or
 * nested expressions that cannot be handled by pet_stmt_build_ast_exprs?
 */
static int print_original(struct pet_scop *scop, struct ppcg_options *options)
{
        if (!pet_scop_can_build_ast_exprs(scop)) {
                if (options->debug->verbose)
                        fprintf(stdout, "Printing original code because "
                                "some index expressions cannot currently "
                                "be printed\n");
                return 1;
        }

        if (pet_scop_has_data_dependent_conditions(scop)) {
                if (options->debug->verbose)
                        fprintf(stdout, "Printing original code because "
                                "input involves data dependent conditions\n");
                return 1;
        }

        return 0;
}

/* Callback for pet_transform_C_source that transforms
 * the given pet_scop to a ppcg_scop before calling the
 * ppcg_transform callback.
 *
 * If "scop" contains any data dependent conditions or if we may
 * not be able to print the transformed program, then just print
 * the original code.
 */
static __isl_give isl_printer *transform(__isl_take isl_printer *p,
        struct pet_scop *scop, void *user)
{
        struct ppcg_transform_data *data = user;
        struct ppcg_scop *ps;

        if (print_original(scop, data->options)) {
                p = pet_scop_print_original(scop, p);
                pet_scop_free(scop);
                return p;
        }

        scop = pet_scop_align_params(scop);
        ps = ppcg_scop_from_pet_scop(scop, data->options);

        p = data->transform(p, ps, data->user);

        ppcg_scop_free(ps);
        pet_scop_free(scop);

        return p;
}

/* Transform the C source file "input" by rewriting each scop
 * through a call to "transform".
 * The transformed C code is written to "out".
 *
 * This is a wrapper around pet_transform_C_source that transforms
 * the pet_scop to a ppcg_scop before calling "fn".
 */
int ppcg_transform(isl_ctx *ctx, const char *input, FILE *out,
        struct ppcg_options *options,
        __isl_give isl_printer *(*fn)(__isl_take isl_printer *p,
                struct ppcg_scop *scop, void *user), void *user)
{
        struct ppcg_transform_data data = { options, fn, user };
        return pet_transform_C_source(ctx, input, out, &transform, &data);
}

/* Check consistency of options.
 *
 * Return -1 on error.
 */
static int check_options(isl_ctx *ctx)
{
        struct options *options;

        options = isl_ctx_peek_options(ctx, &options_args);
        if (!options)
                isl_die(ctx, isl_error_internal,
                        "unable to find options", return -1);

        if (options->ppcg->openmp &&
            !isl_options_get_ast_build_atomic_upper_bound(ctx))
                isl_die(ctx, isl_error_invalid,
                        "OpenMP requires atomic bounds", return -1);

        return 0;
}

int main(int argc, char **argv)
{
        int r;
        isl_ctx *ctx;
        struct options *options;

        options = options_new_with_defaults();
        assert(options);

        ctx = isl_ctx_alloc_with_options(&options_args, options);
        isl_options_set_schedule_outer_coincidence(ctx, 1);
        isl_options_set_schedule_maximize_band_depth(ctx, 1);
        pet_options_set_encapsulate_dynamic_control(ctx, 1);
        argc = options_parse(options, argc, argv, ISL_ARG_ALL);

        if (check_options(ctx) < 0)
                r = EXIT_FAILURE;
        else if (options->ppcg->target == PPCG_TARGET_CUDA)
                r = generate_cuda(ctx, options->ppcg, options->input);
        else if (options->ppcg->target == PPCG_TARGET_OPENCL)
                r = generate_opencl(ctx, options->ppcg, options->input,
                                options->output);
        else
                r = generate_cpu(ctx, options->ppcg, options->input,
                                options->output);

        isl_ctx_free(ctx);

        return r;
}