db/fixup_kernel.sh: fix clear_user() handling

[smatch.git] / smatch_implied.c

/*
 * Copyright (C) 2008 Dan Carpenter.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
 */

/*
 * Imagine we have this code:
 * foo = 1;
 * if (bar)
 *         foo = 99;
 * else
 *         frob();
 *                   //  <-- point #1
 * if (foo == 99)    //  <-- point #2
 *         bar->baz; //  <-- point #3
 *
 *
 * At point #3 bar is non null and can be dereferenced.
 *
 * It's smatch_implied.c which sets bar to non null at point #2.
 *
 * At point #1 merge_slist() stores the list of states from both
 * the true and false paths.  On the true path foo == 99 and on
 * the false path foo == 1.  merge_slist() sets their pool
 * list to show the other states which were there when foo == 99.
 *
 * When it comes to the if (foo == 99) the smatch implied hook
 * looks for all the pools where foo was not 99.  It makes a list
 * of those.
 *
 * Then for bar (and all the other states) it says, ok bar is a
 * merged state that came from these previous states.  We'll
 * chop out all the states where it came from a pool where
 * foo != 99 and merge it all back together.
 *
 * That is the implied state of bar.
 *
 * merge_slist() sets up ->pool.  An sm_state only has one ->pool and
 *    that is the pool where it was first set.  The my pool gets set when
 *    code paths merge.  States that have been set since the last merge do
 *    not have a ->pool.
 * merge_sm_state() sets ->left and ->right.  (These are the states which were
 *    merged to form the current state.)
 * a pool:  a pool is an slist that has been merged with another slist.
 */

#include <time.h>
#include "smatch.h"
#include "smatch_slist.h"
#include "smatch_extra.h"

char *implied_debug_msg;
static char *ignore_implications;

bool implications_off;

bool implied_debug;

#define full_debug 0
#define DIMPLIED(msg...) do { if (full_debug) printf(msg); } while (0)

bool debug_implied(void)
{
        return option_debug || implied_debug || full_debug;
}

void turn_off_implications(int id)
{
        ignore_implications[id] = true;
}

static bool implications_turned_off(int owner)
{
        if (owner >= 0 && owner < num_checks)
                return ignore_implications[owner];
        return false;
}

/*
 * tmp_range_list():
 * It messes things up to free range list allocations.  This helper fuction
 * lets us reuse memory instead of doing new allocations.
 */
static struct range_list *tmp_range_list(struct symbol *type, long long num)
{
        static struct range_list *my_list = NULL;
        static struct data_range *my_range;

        __free_ptr_list((struct ptr_list **)&my_list);
        my_range = alloc_range(ll_to_sval(num), ll_to_sval(num));
        add_ptr_list(&my_list, my_range);
        return my_list;
}

static const char *show_comparison(int op)
{
        if (op == PARAM_LIMIT)
                return "<lim>";
        return show_special(op);
}

static void print_debug_tf(struct sm_state *sm, int istrue, int isfalse)
{
        if (!full_debug && !option_debug)
                return;

        if (istrue && isfalse) {
                printf("%s: %d: does not exist.\n", show_sm(sm), sm->line);
        } else if (istrue) {
                printf("'%s = %s' from %d is true. %s[stree %d]\n", sm->name, show_state(sm->state),
                        sm->line, sm->merged ? "[merged]" : "[leaf]",
                        get_stree_id(sm->pool));
        } else if (isfalse) {
                printf("'%s = %s' from %d is false. %s[stree %d]\n", sm->name, show_state(sm->state),
                        sm->line,
                        sm->merged ? "[merged]" : "[leaf]",
                        get_stree_id(sm->pool));
        } else {
                printf("'%s = %s' from %d could be true or false. %s[stree %d]\n", sm->name,
                        show_state(sm->state), sm->line,
                        sm->merged ? "[merged]" : "[leaf]",
                        get_stree_id(sm->pool));
        }
}

void split_comparison_helper(struct range_list *left_orig, int op, struct range_list *right_orig,
                struct range_list **left_true_rl, struct range_list **left_false_rl)
{
        if (op == PARAM_LIMIT) {
                *left_true_rl = rl_intersection(left_orig, right_orig);
                *left_false_rl = rl_filter(left_orig, right_orig);
                return;
        }

        split_comparison_rl(left_orig, op, right_orig, left_true_rl, left_false_rl, NULL, NULL);
}

static int create_fake_history(struct sm_state *sm, int comparison, struct range_list *rl)
{
        struct range_list *orig_rl;
        struct range_list *true_rl, *false_rl;
        struct stree *true_stree, *false_stree;
        struct sm_state *true_sm, *false_sm;
        sval_t sval;

        if (is_merged(sm) || sm->left || sm->right)
                return 0;
        if (comparison != PARAM_LIMIT && !rl_to_sval(rl, &sval))
                return 0;
        if (!estate_rl(sm->state))
                return 0;

        orig_rl = cast_rl(rl_type(rl), estate_rl(sm->state));
        split_comparison_helper(orig_rl, comparison, rl, &true_rl, &false_rl);

        true_rl = rl_truncate_cast(estate_type(sm->state), true_rl);
        false_rl = rl_truncate_cast(estate_type(sm->state), false_rl);
        if (is_whole_rl(true_rl) || is_whole_rl(false_rl) ||
            !true_rl || !false_rl ||
            rl_equiv(orig_rl, true_rl) || rl_equiv(orig_rl, false_rl) ||
            rl_equiv(estate_rl(sm->state), true_rl) || rl_equiv(estate_rl(sm->state), false_rl))
                return 0;

        if (rl_intersection(true_rl, false_rl)) {
                /*
                 * Normally these won't intersect, but one exception is when
                 * we're dealing with mtags.  We have a long list of mtags and
                 * then negate the list.  Now it's over the limit for mtag list
                 * length and we squash it down to 4096-ptr_max.  So then it's
                 * possible for the true and false rl to overlap.
                 */
                return 0;
        }

        if (full_debug)
                sm_msg("fake_history: %s vs %s.  %s %s %s. --> T: %s F: %s",
                       sm->name, show_rl(rl), sm->state->name, show_comparison(comparison), show_rl(rl),
                       show_rl(true_rl), show_rl(false_rl));

        true_sm = clone_sm(sm);
        false_sm = clone_sm(sm);

        true_sm->state = clone_partial_estate(sm->state, true_rl);
        free_slist(&true_sm->possible);
        add_possible_sm(true_sm, true_sm);
        false_sm->state = clone_partial_estate(sm->state, false_rl);
        free_slist(&false_sm->possible);
        add_possible_sm(false_sm, false_sm);

        true_stree = clone_stree(sm->pool);
        false_stree = clone_stree(sm->pool);

        overwrite_sm_state_stree(&true_stree, true_sm);
        overwrite_sm_state_stree(&false_stree, false_sm);

        true_sm->pool = true_stree;
        false_sm->pool = false_stree;

        sm->leaf = 1;
        sm->merged = 1;
        sm->left = true_sm;
        sm->right = false_sm;

        return 1;
}

/*
 * add_pool() adds a slist to *pools. If the slist has already been
 * added earlier then it doesn't get added a second time.
 */
void add_pool(struct state_list **pools, struct sm_state *new)
{
        struct sm_state *tmp;

        FOR_EACH_PTR(*pools, tmp) {
                if (tmp->pool < new->pool)
                        continue;
                else if (tmp->pool == new->pool) {
                        return;
                } else {
                        INSERT_CURRENT(new, tmp);
                        return;
                }
        } END_FOR_EACH_PTR(tmp);
        add_ptr_list(pools, new);
}

static int pool_in_pools(struct stree *pool,
                         const struct state_list *slist)
{
        struct sm_state *tmp;

        FOR_EACH_PTR(slist, tmp) {
                if (!tmp->pool)
                        continue;
                if (tmp->pool == pool)
                        return 1;
        } END_FOR_EACH_PTR(tmp);
        return 0;
}

static int remove_pool(struct state_list **pools, struct stree *remove)
{
        struct sm_state *tmp;
        int ret = 0;

        FOR_EACH_PTR(*pools, tmp) {
                if (tmp->pool == remove) {
                        DELETE_CURRENT_PTR(tmp);
                        ret = 1;
                }
        } END_FOR_EACH_PTR(tmp);

        return ret;
}

static bool possibly_true_helper(struct range_list *var_rl, int comparison, struct range_list *rl)
{
        if (comparison == PARAM_LIMIT) {
                struct range_list *intersect;

                intersect = rl_intersection(var_rl, rl);
                if (intersect)
                        return true;
                return false;
        }
        return possibly_true_rl(var_rl, comparison, rl);
}

static bool possibly_false_helper(struct range_list *var_rl, int comparison, struct range_list *rl)
{
        if (comparison == PARAM_LIMIT) {
                struct range_list *intersect;

                intersect = rl_intersection(var_rl, rl);
                /* if it's not equiv then it's possibly false */
                return !rl_equiv(var_rl, intersect);
        }
        return possibly_false_rl(var_rl, comparison, rl);
}

/*
 * If 'foo' == 99 add it that pool to the true pools.  If it's false, add it to
 * the false pools.  If we're not sure, then we don't add it to either.
 */
static void do_compare(struct sm_state *sm, int comparison, struct range_list *rl,
                        struct state_list **true_stack,
                        struct state_list **maybe_stack,
                        struct state_list **false_stack,
                        int *mixed, struct sm_state *gate_sm)
{
        int istrue;
        int isfalse;
        struct range_list *var_rl;

        if (!sm->pool)
                return;

        var_rl = cast_rl(rl_type(rl), estate_rl(sm->state));

        istrue = !possibly_false_helper(var_rl, comparison, rl);
        isfalse = !possibly_true_helper(var_rl, comparison, rl);

        print_debug_tf(sm, istrue, isfalse);

        /* give up if we have borrowed implications (smatch_equiv.c) */
        if (sm->sym != gate_sm->sym ||
            strcmp(sm->name, gate_sm->name) != 0) {
                if (mixed)
                        *mixed = 1;
        }

        if (mixed && !*mixed && !is_merged(sm) && !istrue && !isfalse) {
                if (!create_fake_history(sm, comparison, rl))
                        *mixed = 1;
        }

        if (istrue)
                add_pool(true_stack, sm);
        else if (isfalse)
                add_pool(false_stack, sm);
        else
                add_pool(maybe_stack, sm);
}

static int is_checked(struct state_list *checked, struct sm_state *sm)
{
        struct sm_state *tmp;

        FOR_EACH_PTR(checked, tmp) {
                if (tmp == sm)
                        return 1;
        } END_FOR_EACH_PTR(tmp);
        return 0;
}

/*
 * separate_pools():
 * Example code:  if (foo == 99) {
 *
 * Say 'foo' is a merged state that has many possible values.  It is the combination
 * of merges.  separate_pools() iterates through the pools recursively and calls
 * do_compare() for each time 'foo' was set.
 */
static void __separate_pools(struct sm_state *sm, int comparison, struct range_list *rl,
                        struct state_list **true_stack,
                        struct state_list **maybe_stack,
                        struct state_list **false_stack,
                        struct state_list **checked, int *mixed, struct sm_state *gate_sm,
                        struct timeval *start_time)
{
        int free_checked = 0;
        struct state_list *checked_states = NULL;
        struct timeval now, diff;

        if (!sm)
                return;

        gettimeofday(&now, NULL);
        timersub(&now, start_time, &diff);
        if (diff.tv_sec >= 1) {
                if (full_debug) {
                        sm_msg("debug: %s: implications taking too long.  (%s %s %s)",
                               __func__, sm->state->name, show_comparison(comparison), show_rl(rl));
                }
                if (mixed)
                        *mixed = 1;
        }

        if (checked == NULL) {
                checked = &checked_states;
                free_checked = 1;
        }
        if (is_checked(*checked, sm))
                return;
        add_ptr_list(checked, sm);

        do_compare(sm, comparison, rl, true_stack, maybe_stack, false_stack, mixed, gate_sm);

        __separate_pools(sm->left, comparison, rl, true_stack, maybe_stack, false_stack, checked, mixed, gate_sm, start_time);
        __separate_pools(sm->right, comparison, rl, true_stack, maybe_stack, false_stack, checked, mixed, gate_sm, start_time);
        if (free_checked)
                free_slist(checked);
}

static void separate_pools(struct sm_state *sm, int comparison, struct range_list *rl,
                        struct state_list **true_stack,
                        struct state_list **false_stack,
                        struct state_list **checked, int *mixed)
{
        struct state_list *maybe_stack = NULL;
        struct sm_state *tmp;
        struct timeval start_time;


        gettimeofday(&start_time, NULL);
        __separate_pools(sm, comparison, rl, true_stack, &maybe_stack, false_stack, checked, mixed, sm, &start_time);

        if (full_debug) {
                struct sm_state *sm;

                FOR_EACH_PTR(*true_stack, sm) {
                        sm_msg("TRUE %s [stree %d %p]", show_sm(sm), get_stree_id(sm->pool), sm->pool);
                } END_FOR_EACH_PTR(sm);

                FOR_EACH_PTR(maybe_stack, sm) {
                        sm_msg("MAYBE %s %s[stree %d %p]",
                               show_sm(sm), sm->merged ? "(merged) ": "", get_stree_id(sm->pool), sm->pool);
                } END_FOR_EACH_PTR(sm);

                FOR_EACH_PTR(*false_stack, sm) {
                        sm_msg("FALSE %s [stree %d %p]", show_sm(sm), get_stree_id(sm->pool), sm->pool);
                } END_FOR_EACH_PTR(sm);
        }
        /* if it's a maybe then remove it */
        FOR_EACH_PTR(maybe_stack, tmp) {
                remove_pool(false_stack, tmp->pool);
                remove_pool(true_stack, tmp->pool);
        } END_FOR_EACH_PTR(tmp);

        /* if it's both true and false remove it from both */
        FOR_EACH_PTR(*true_stack, tmp) {
                if (remove_pool(false_stack, tmp->pool))
                        DELETE_CURRENT_PTR(tmp);
        } END_FOR_EACH_PTR(tmp);
}

static int sm_in_keep_leafs(struct sm_state *sm, const struct state_list *keep_gates)
{
        struct sm_state *tmp, *old;

        FOR_EACH_PTR(keep_gates, tmp) {
                if (!is_leaf(tmp))
                        continue;
                old = get_sm_state_stree(tmp->pool, sm->owner, sm->name, sm->sym);
                if (!old)
                        continue;
                if (old == sm)
                        return 1;
        } END_FOR_EACH_PTR(tmp);
        return 0;
}

static int going_too_slow(void)
{
        static void *printed;

        if (out_of_memory()) {
                implications_off = true;
                return 1;
        }

        if (time_parsing_function() < 60) {
                implications_off = false;
                return 0;
        }

        if (!__inline_fn && printed != cur_func_sym) {
                sm_perror("turning off implications after 60 seconds");
                printed = cur_func_sym;
        }
        implications_off = true;
        return 1;
}

static char *sm_state_info(struct sm_state *sm)
{
        static char buf[512];
        int n = 0;

        n += snprintf(buf + n, sizeof(buf) - n, "[stree %d line %d] ",
                      get_stree_id(sm->pool),  sm->line);
        if (n >= sizeof(buf))
                return buf;
        n += snprintf(buf + n, sizeof(buf) - n, "%s ", show_sm(sm));
        if (n >= sizeof(buf))
                return buf;
        n += snprintf(buf + n, sizeof(buf) - n, "left = %s [stree %d] ",
                      sm->left ? sm->left->state->name : "<none>",
                      sm->left ? get_stree_id(sm->left->pool) : -1);
        if (n >= sizeof(buf))
                return buf;
        n += snprintf(buf + n, sizeof(buf) - n, "right = %s [stree %d]",
                      sm->right ? sm->right->state->name : "<none>",
                      sm->right ? get_stree_id(sm->right->pool) : -1);
        return buf;
}

/*
 * NOTE: If a state is in both the keep stack and the remove stack then that is
 * a bug.  Only add states which are definitely true or definitely false.  If
 * you have a leaf state that could be both true and false, then create a fake
 * split history where one side is true and one side is false.  Otherwise, if
 * you can't do that, then don't add it to either list.
 */
#define RECURSE_LIMIT 300
struct sm_state *filter_pools(struct sm_state *sm,
                              const struct state_list *remove_stack,
                              const struct state_list *keep_stack,
                              int *modified, int *recurse_cnt,
                              struct timeval *start, int *skip, int *bail)
{
        struct sm_state *ret = NULL;
        struct sm_state *left;
        struct sm_state *right;
        int removed = 0;
        struct timeval now, diff;

        if (!sm)
                return NULL;
        if (*bail)
                return NULL;
        gettimeofday(&now, NULL);
        timersub(&now, start, &diff);
        if (diff.tv_sec >= 3) {
                DIMPLIED("%s: implications taking too long: %s\n", __func__, sm_state_info(sm));
                *bail = 1;
                return NULL;
        }
        if ((*recurse_cnt)++ > RECURSE_LIMIT) {
                DIMPLIED("%s: recursed too far:  %s\n", __func__, sm_state_info(sm));
                *skip = 1;
                return NULL;
        }

        if (pool_in_pools(sm->pool, remove_stack)) {
                DIMPLIED("%s: remove: %s\n", __func__, sm_state_info(sm));
                *modified = 1;
                return NULL;
        }

        if (!is_merged(sm) || pool_in_pools(sm->pool, keep_stack) || sm_in_keep_leafs(sm, keep_stack)) {
                DIMPLIED("%s: keep %s (%s, %s, %s): %s\n", __func__, sm->state->name,
                        is_merged(sm) ? "merged" : "not merged",
                        pool_in_pools(sm->pool, keep_stack) ? "in keep pools" : "not in keep pools",
                        sm_in_keep_leafs(sm, keep_stack) ? "reachable keep leaf" : "no keep leaf",
                        sm_state_info(sm));
                return sm;
        }

        left = filter_pools(sm->left, remove_stack, keep_stack, &removed, recurse_cnt, start, skip, bail);
        right = filter_pools(sm->right, remove_stack, keep_stack, &removed, recurse_cnt, start, skip, bail);
        if (*bail || *skip)
                return NULL;
        if (!removed) {
                DIMPLIED("%s: kept all: %s\n", __func__, sm_state_info(sm));
                return sm;
        }
        *modified = 1;
        if (!left && !right) {
                DIMPLIED("%s: removed all: %s\n", __func__, sm_state_info(sm));
                return NULL;
        }

        if (!left) {
                ret = clone_sm(right);
                ret->merged = 1;
                ret->right = right;
                ret->left = NULL;
        } else if (!right) {
                ret = clone_sm(left);
                ret->merged = 1;
                ret->left = left;
                ret->right = NULL;
        } else {
                if (left->sym != sm->sym || strcmp(left->name, sm->name) != 0) {
                        left = clone_sm(left);
                        left->sym = sm->sym;
                        left->name = sm->name;
                }
                if (right->sym != sm->sym || strcmp(right->name, sm->name) != 0) {
                        right = clone_sm(right);
                        right->sym = sm->sym;
                        right->name = sm->name;
                }
                ret = merge_sm_states(left, right);
        }

        ret->pool = sm->pool;

        DIMPLIED("%s: partial: %s\n", __func__, sm_state_info(sm));
        return ret;
}

static struct stree *filter_stack(struct sm_state *gate_sm,
                                  struct stree *pre_stree,
                                  const struct state_list *remove_stack,
                                  const struct state_list *keep_stack)
{
        struct stree *ret = NULL;
        struct sm_state *tmp;
        struct sm_state *filtered_sm;
        int modified;
        int recurse_cnt;
        struct timeval start;
        int skip;
        int bail = 0;

        if (!remove_stack)
                return NULL;

        gettimeofday(&start, NULL);
        FOR_EACH_SM(pre_stree, tmp) {
                if (!tmp->merged || sm_in_keep_leafs(tmp, keep_stack))
                        continue;
                modified = 0;
                recurse_cnt = 0;
                skip = 0;
                filtered_sm = filter_pools(tmp, remove_stack, keep_stack, &modified, &recurse_cnt, &start, &skip, &bail);
                if (going_too_slow())
                        return NULL;
                if (bail)
                        return ret;  /* Return the implications we figured out before time ran out. */


                if (skip || !filtered_sm || !modified)
                        continue;
                /* the assignments here are for borrowed implications */
                filtered_sm->name = tmp->name;
                filtered_sm->sym = tmp->sym;
                avl_insert(&ret, filtered_sm);
        } END_FOR_EACH_SM(tmp);
        return ret;
}

static void separate_and_filter(struct sm_state *sm, int comparison, struct range_list *rl,
                struct stree *pre_stree,
                struct stree **true_states,
                struct stree **false_states,
                int *mixed)
{
        struct state_list *true_stack = NULL;
        struct state_list *false_stack = NULL;
        struct timeval time_before;
        struct timeval time_after;
        int sec;

        gettimeofday(&time_before, NULL);

        DIMPLIED("checking implications: (%s (%s) %s %s)\n",
                 sm->name, sm->state->name, show_comparison(comparison), show_rl(rl));

        if (!is_merged(sm)) {
                DIMPLIED("%d '%s' from line %d is not merged.\n", get_lineno(), sm->name, sm->line);
                return;
        }

        separate_pools(sm, comparison, rl, &true_stack, &false_stack, NULL, mixed);

        if (full_debug) {
                struct sm_state *sm;

                FOR_EACH_PTR(true_stack, sm) {
                        sm_msg("TRUE POOL: %p", sm->pool);
                } END_FOR_EACH_PTR(sm);

                FOR_EACH_PTR(false_stack, sm) {
                        sm_msg("FALSE POOL: %p", sm->pool);
                } END_FOR_EACH_PTR(sm);
        }

        DIMPLIED("filtering true stack.\n");
        *true_states = filter_stack(sm, pre_stree, false_stack, true_stack);
        DIMPLIED("filtering false stack.\n");
        *false_states = filter_stack(sm, pre_stree, true_stack, false_stack);
        free_slist(&true_stack);
        free_slist(&false_stack);

        gettimeofday(&time_after, NULL);
        sec = time_after.tv_sec - time_before.tv_sec;
        if (sec > 20)
                sm_perror("Function too hairy.  Ignoring implications after %d seconds.", sec);
}

static struct expression *get_last_expr(struct statement *stmt)
{
        struct statement *last;

        last = last_ptr_list((struct ptr_list *)stmt->stmts);
        if (last->type == STMT_EXPRESSION)
                return last->expression;

        if (last->type == STMT_LABEL) {
                if (last->label_statement &&
                    last->label_statement->type == STMT_EXPRESSION)
                        return last->label_statement->expression;
        }

        return NULL;
}

static struct expression *get_left_most_expr(struct expression *expr)
{
        struct statement *compound;
        struct expression *fake;

        compound = get_expression_statement(expr);
        if (compound)
                return get_last_expr(compound);

        expr = strip_parens(expr);
        if (expr->type == EXPR_ASSIGNMENT)
                return get_left_most_expr(expr->left);
        fake = expr_get_fake_parent_expr(expr);
        if (fake && fake->type == EXPR_ASSIGNMENT)
                return fake->left;
        return expr;
}

static int is_merged_expr(struct expression  *expr)
{
        struct sm_state *sm;
        sval_t dummy;

        if (get_value(expr, &dummy))
                return 0;
        sm = get_sm_state_expr(SMATCH_EXTRA, expr);
        if (!sm)
                return 0;
        if (is_merged(sm))
                return 1;
        return 0;
}

static void delete_gate_sm_equiv(struct stree **stree, const char *name, struct symbol *sym)
{
        struct smatch_state *state;
        struct relation *rel;

        state = get_state(SMATCH_EXTRA, name, sym);
        if (!state)
                return;
        FOR_EACH_PTR(estate_related(state), rel) {
                delete_state_stree(stree, SMATCH_EXTRA, rel->name, rel->sym);
        } END_FOR_EACH_PTR(rel);
}

static void delete_gate_sm(struct stree **stree, const char *name, struct symbol *sym)
{
        delete_state_stree(stree, SMATCH_EXTRA, name, sym);
}

static int handle_comparison(struct expression *expr,
                              struct stree **implied_true,
                              struct stree **implied_false)
{
        struct sm_state *sm = NULL;
        struct range_list *rl = NULL;
        struct expression *left;
        struct expression *right;
        struct symbol *type;
        int comparison = expr->op;
        int mixed = 0;

        left = get_left_most_expr(expr->left);
        right = get_left_most_expr(expr->right);

        if (is_merged_expr(left)) {
                sm = get_sm_state_expr(SMATCH_EXTRA, left);
                get_implied_rl(right, &rl);
        } else if (is_merged_expr(right)) {
                sm = get_sm_state_expr(SMATCH_EXTRA, right);
                get_implied_rl(left, &rl);
                comparison = flip_comparison(comparison);
        }

        if (!rl || !sm)
                return 0;

        type = get_type(expr);
        if (!type)
                return 0;
        if (type_positive_bits(rl_type(rl)) > type_positive_bits(type))
                type = rl_type(rl);
        if (type_positive_bits(type) < 31)
                type = &int_ctype;
        rl = cast_rl(type, rl);

        separate_and_filter(sm, comparison, rl, __get_cur_stree(), implied_true, implied_false, &mixed);

        delete_gate_sm_equiv(implied_true, sm->name, sm->sym);
        delete_gate_sm_equiv(implied_false, sm->name, sm->sym);
        if (mixed) {
                delete_gate_sm(implied_true, sm->name, sm->sym);
                delete_gate_sm(implied_false, sm->name, sm->sym);
        }

        return 1;
}

static int handle_zero_comparison(struct expression *expr,
                                struct stree **implied_true,
                                struct stree **implied_false)
{
        struct symbol *sym;
        char *name;
        struct sm_state *sm;
        int mixed = 0;
        int ret = 0;

        if (expr->type == EXPR_POSTOP)
                expr = strip_expr(expr->unop);

        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;
        sm = get_sm_state(SMATCH_EXTRA, name, sym);
        if (!sm || !sm->merged)
                goto free;

        separate_and_filter(sm, SPECIAL_NOTEQUAL, tmp_range_list(estate_type(sm->state), 0), __get_cur_stree(), implied_true, implied_false, &mixed);
        delete_gate_sm_equiv(implied_true, sm->name, sm->sym);
        delete_gate_sm_equiv(implied_false, sm->name, sm->sym);
        if (mixed) {
                delete_gate_sm(implied_true, sm->name, sm->sym);
                delete_gate_sm(implied_false, sm->name, sm->sym);
        }

        ret = 1;
free:
        free_string(name);
        return ret;
}

static int handled_by_comparison_hook(struct expression *expr,
                                      struct stree **implied_true,
                                      struct stree **implied_false)
{
        struct sm_state *sm, *true_sm, *false_sm;
        struct state_list *true_stack = NULL;
        struct state_list *false_stack = NULL;
        struct stree *pre_stree;

        sm = comparison_implication_hook(expr, &true_stack, &false_stack);
        if (!sm)
                return 0;

        pre_stree = clone_stree(__get_cur_stree());

        *implied_true = filter_stack(sm, pre_stree, false_stack, true_stack);
        *implied_false = filter_stack(sm, pre_stree, true_stack, false_stack);

        true_sm = get_sm_state_stree(*implied_true, sm->owner, sm->name, sm->sym);
        false_sm = get_sm_state_stree(*implied_false, sm->owner, sm->name, sm->sym);
        if (true_sm && strcmp(true_sm->state->name, "unknown") == 0)
                delete_state_stree(implied_true, sm->owner, sm->name, sm->sym);
        if (false_sm && strcmp(false_sm->state->name, "unknown") == 0)
                delete_state_stree(implied_false, sm->owner, sm->name, sm->sym);

        free_stree(&pre_stree);
        free_slist(&true_stack);
        free_slist(&false_stack);

        return 1;
}

static int handled_by_extra_states(struct expression *expr,
                                   struct stree **implied_true,
                                   struct stree **implied_false)
{
        sval_t sval;

        /* If the expression is known then it has no implications.  */
        if (get_implied_value(expr, &sval))
                return true;

        if (expr->type == EXPR_COMPARE)
                return handle_comparison(expr, implied_true, implied_false);
        else
                return handle_zero_comparison(expr, implied_true, implied_false);
}

static int handled_by_parsed_conditions(struct expression *expr,
                                        struct stree **implied_true,
                                        struct stree **implied_false)
{
        struct state_list *true_stack = NULL;
        struct state_list *false_stack = NULL;
        struct stree *pre_stree;
        struct sm_state *sm;

        sm = parsed_condition_implication_hook(expr, &true_stack, &false_stack);
        if (!sm)
                return 0;

        pre_stree = clone_stree(__get_cur_stree());

        *implied_true = filter_stack(sm, pre_stree, false_stack, true_stack);
        *implied_false = filter_stack(sm, pre_stree, true_stack, false_stack);

        free_stree(&pre_stree);
        free_slist(&true_stack);
        free_slist(&false_stack);

        return 1;
}

static int handled_by_stored_conditions(struct expression *expr,
                                        struct stree **implied_true,
                                        struct stree **implied_false)
{
        struct state_list *true_stack = NULL;
        struct state_list *false_stack = NULL;
        struct stree *pre_stree;
        struct sm_state *sm;

        sm = stored_condition_implication_hook(expr, &true_stack, &false_stack);
        if (!sm)
                return 0;

        pre_stree = clone_stree(__get_cur_stree());

        *implied_true = filter_stack(sm, pre_stree, false_stack, true_stack);
        *implied_false = filter_stack(sm, pre_stree, true_stack, false_stack);

        free_stree(&pre_stree);
        free_slist(&true_stack);
        free_slist(&false_stack);

        return 1;
}

static struct stree *saved_implied_true;
static struct stree *saved_implied_false;
static struct stree *extra_saved_implied_true;
static struct stree *extra_saved_implied_false;

static void separate_implication_states(struct stree **implied_true,
                                         struct stree **implied_false,
                                         int owner)
{
        struct sm_state *sm;

        /* We process these states later to preserve the implications. */
        FOR_EACH_SM(*implied_true, sm) {
                if (sm->owner == owner)
                        overwrite_sm_state_stree(&extra_saved_implied_true, sm);
        } END_FOR_EACH_SM(sm);
        FOR_EACH_SM(extra_saved_implied_true, sm) {
                delete_state_stree(implied_true, sm->owner, sm->name, sm->sym);
        } END_FOR_EACH_SM(sm);

        FOR_EACH_SM(*implied_false, sm) {
                if (sm->owner == owner)
                        overwrite_sm_state_stree(&extra_saved_implied_false, sm);
        } END_FOR_EACH_SM(sm);
        FOR_EACH_SM(extra_saved_implied_false, sm) {
                delete_state_stree(implied_false, sm->owner, sm->name, sm->sym);
        } END_FOR_EACH_SM(sm);
}

static void get_tf_states(struct expression *expr,
                          struct stree **implied_true,
                          struct stree **implied_false)
{
        while (expr->type == EXPR_ASSIGNMENT && expr->op == '=')
                expr = strip_parens(expr->left);

        if (handled_by_parsed_conditions(expr, implied_true, implied_false))
                return;

        if (handled_by_comparison_hook(expr, implied_true, implied_false)) {
                separate_implication_states(implied_true, implied_false, comparison_id);
                return;
        }

        if (handled_by_extra_states(expr, implied_true, implied_false)) {
                separate_implication_states(implied_true, implied_false, SMATCH_EXTRA);
                return;
        }

        if (handled_by_stored_conditions(expr, implied_true, implied_false))
                return;
}

static void save_implications_hook(struct expression *expr)
{
        if (going_too_slow())
                return;
        get_tf_states(expr, &saved_implied_true, &saved_implied_false);
}

static void set_implied_states(struct expression *expr)
{
        struct sm_state *sm;

        if ((full_debug || implied_debug) &&
            (saved_implied_true || saved_implied_false)) {
                char *name;

                name = expr_to_str(expr);
                printf("These are the implied states for the true path: (%s)\n", name);
                __print_stree(saved_implied_true);
                printf("These are the implied states for the false path: (%s)\n", name);
                __print_stree(saved_implied_false);
                free_string(name);
        }

        FOR_EACH_SM(saved_implied_true, sm) {
                if (implications_turned_off(sm->owner))
                        continue;
                __set_true_false_sm(sm, NULL);
        } END_FOR_EACH_SM(sm);
        free_stree(&saved_implied_true);

        FOR_EACH_SM(saved_implied_false, sm) {
                if (implications_turned_off(sm->owner))
                        continue;
                __set_true_false_sm(NULL, sm);
        } END_FOR_EACH_SM(sm);
        free_stree(&saved_implied_false);
}

static void set_extra_implied_states(struct expression *expr)
{
        saved_implied_true = extra_saved_implied_true;
        saved_implied_false = extra_saved_implied_false;
        extra_saved_implied_true = NULL;
        extra_saved_implied_false = NULL;
        set_implied_states(expr);
}

void param_limit_implications(struct expression *expr, int param, char *key, char *value, struct stree **implied)
{
        struct expression *orig_expr, *arg;
        struct symbol *compare_type;
        char *name;
        struct symbol *sym;
        struct sm_state *sm;
        struct sm_state *tmp;
        struct stree *implied_true = NULL;
        struct stree *implied_false = NULL;
        struct range_list *orig, *limit;
        char *left_name = NULL;
        struct symbol *left_sym = NULL;
        int mixed = 0;

        if (time_parsing_function() > 40)
                return;

        orig_expr = expr;
        while (expr->type == EXPR_ASSIGNMENT)
                expr = strip_expr(expr->right);
        if (expr->type != EXPR_CALL)
                return;

        arg = get_argument_from_call_expr(expr->args, param);
        if (!arg)
                return;

        arg = strip_parens(arg);
        while (arg->type == EXPR_ASSIGNMENT && arg->op == '=')
                arg = strip_parens(arg->left);

        name = get_variable_from_key(arg, key, &sym);
        if (!name || !sym)
                goto free;

        sm = get_sm_state(SMATCH_EXTRA, name, sym);
        if (!sm || !sm->merged)
                goto free;

        if (strcmp(key, "$") == 0)
                compare_type = get_arg_type(expr->fn, param);
        else
                compare_type = get_member_type_from_key(arg, key);

        orig = estate_rl(sm->state);
        orig = cast_rl(compare_type, orig);

        call_results_to_rl(expr, compare_type, value, &limit);

        separate_and_filter(sm, PARAM_LIMIT, limit, __get_cur_stree(), &implied_true, &implied_false, &mixed);

        if (orig_expr->type == EXPR_ASSIGNMENT)
                left_name = expr_to_var_sym(orig_expr->left, &left_sym);

        FOR_EACH_SM(implied_true, tmp) {

                if (implied_debug)
                        sm_msg("param_implication: param='%s' limit='%s' sm='%s'", name, show_rl(limit), show_sm(tmp));

                if (implications_turned_off(tmp->owner))
                        continue;

                /*
                 * What we're trying to do here is preserve the sm state so that
                 * smatch extra doesn't create a new sm state when it parses the
                 * PARAM_LIMIT.
                 */
                if (!mixed && tmp->sym == sym &&
                    strcmp(tmp->name, name) == 0 &&
                    (!left_name || strcmp(left_name, name) != 0)) {
                        overwrite_sm_state_stree(implied, tmp);
                        continue;
                }

                __set_sm(tmp);
        } END_FOR_EACH_SM(tmp);

        free_stree(&implied_true);
        free_stree(&implied_false);
free:
        free_string(name);
}

struct stree *__implied_case_stree(struct expression *switch_expr,
                                   struct range_list *rl,
                                   struct range_list_stack **remaining_cases,
                                   struct stree **raw_stree)
{
        char *name;
        struct symbol *sym;
        struct var_sym_list *vsl;
        struct sm_state *sm;
        struct stree *true_states = NULL;
        struct stree *false_states = NULL;
        struct stree *extra_states;
        struct stree *ret = clone_stree(*raw_stree);

        name = expr_to_chunk_sym_vsl(switch_expr, &sym, &vsl);

        if (rl)
                filter_top_rl(remaining_cases, rl);
        else
                rl = clone_rl(top_rl(*remaining_cases));

        if (name) {
                sm = get_sm_state_stree(*raw_stree, SMATCH_EXTRA, name, sym);
                if (sm)
                        separate_and_filter(sm, SPECIAL_EQUAL, rl, *raw_stree, &true_states, &false_states, NULL);
        }

        __push_fake_cur_stree();
        __unnullify_path();
        if (name)
                set_extra_nomod_vsl(name, sym, vsl, NULL, alloc_estate_rl(rl));
        __pass_case_to_client(switch_expr, rl);
        extra_states = __pop_fake_cur_stree();
        overwrite_stree(extra_states, &true_states);
        overwrite_stree(true_states, &ret);
        free_stree(&extra_states);
        free_stree(&true_states);
        free_stree(&false_states);

        free_string(name);
        return ret;
}

static void match_end_func(struct symbol *sym)
{
        if (__inline_fn)
                return;
        implied_debug_msg = NULL;
}

static void get_tf_stacks_from_pool(struct sm_state *gate_sm,
                                    struct sm_state *pool_sm,
                                    struct state_list **true_stack,
                                    struct state_list **false_stack)
{
        struct sm_state *tmp;
        int possibly_true = 0;

        if (!gate_sm)
                return;

        if (is_leaf(gate_sm) &&
            strcmp(gate_sm->state->name, pool_sm->state->name) == 0) {
                add_ptr_list(true_stack, pool_sm);
                return;
        }

        FOR_EACH_PTR(gate_sm->possible, tmp) {
                if (strcmp(tmp->state->name, pool_sm->state->name) == 0) {
                        possibly_true = 1;
                        break;
                }
        } END_FOR_EACH_PTR(tmp);

        if (!possibly_true) {
                add_ptr_list(false_stack, gate_sm);
                return;
        }

        get_tf_stacks_from_pool(gate_sm->left, pool_sm, true_stack, false_stack);
        get_tf_stacks_from_pool(gate_sm->right, pool_sm, true_stack, false_stack);
}

/*
 * The situation is we have a SMATCH_EXTRA state and we want to break it into
 * each of the ->possible states and find the implications of each.  The caller
 * has to use __push_fake_cur_stree() to preserve the correct states so they
 * can be restored later.
 */
void overwrite_states_using_pool(struct sm_state *gate_sm, struct sm_state *pool_sm)
{
        struct state_list *true_stack = NULL;
        struct state_list *false_stack = NULL;
        struct stree *pre_stree;
        struct stree *implied_true;
        struct sm_state *tmp;

        if (!pool_sm->pool)
                return;

        get_tf_stacks_from_pool(gate_sm, pool_sm, &true_stack, &false_stack);

        pre_stree = clone_stree(__get_cur_stree());

        implied_true = filter_stack(gate_sm, pre_stree, false_stack, true_stack);

        free_stree(&pre_stree);
        free_slist(&true_stack);
        free_slist(&false_stack);

        FOR_EACH_SM(implied_true, tmp) {
                __set_sm(tmp);
        } END_FOR_EACH_SM(tmp);

        free_stree(&implied_true);
}

int assume(struct expression *expr)
{
        int orig_final_pass = final_pass;

        in_fake_env++;
        final_pass = 0;
        __push_fake_cur_stree();
        __split_whole_condition(expr);
        final_pass = orig_final_pass;
        in_fake_env--;

        return 1;
}

void end_assume(void)
{
        __discard_false_states();
        __free_fake_cur_stree();
}

int impossible_assumption(struct expression *left, int op, sval_t sval)
{
        struct expression *value;
        struct expression *comparison;
        int ret;

        value = value_expr(sval.value);
        comparison = compare_expression(left, op, value);

        if (!assume(comparison))
                return 0;
        ret = is_impossible_path();
        end_assume();

        return ret;
}

void __extra_match_condition(struct expression *expr);
void __comparison_match_condition(struct expression *expr);
void __stored_condition(struct expression *expr);
void register_implications(int id)
{
        ignore_implications = malloc(num_checks);
        memset(ignore_implications, 0, num_checks);

        add_hook(&save_implications_hook, CONDITION_HOOK);
        add_hook(&set_implied_states, CONDITION_HOOK);
        add_hook(&__extra_match_condition, CONDITION_HOOK);
        add_hook(&__comparison_match_condition, CONDITION_HOOK);
        add_hook(&set_extra_implied_states, CONDITION_HOOK);
        add_hook(&__stored_condition, CONDITION_HOOK);
        add_hook(&match_end_func, END_FUNC_HOOK);
}