unreachable code: don't warn about unreachable break statements

[smatch.git] / smatch_states.c

/*
 * sparse/smatch_states.c
 *
 * Copyright (C) 2006 Dan Carpenter.
 *
 * Licensed under the Open Software License version 1.1
 *
 */

/*
 * You have a lists of states.  kernel = locked, foo = NULL, ...
 * When you hit an if {} else {} statement then you swap the list
 * of states for a different list of states.  The lists are stored
 * on stacks.
 *
 * At the beginning of this file there are list of the stacks that
 * we use.  Each function in this file does something to one of
 * of the stacks.
 *
 * So the smatch_flow.c understands code but it doesn't understand states.
 * smatch_flow calls functions in this file.  This file calls functions
 * in smatch_slist.c which just has boring generic plumbing for handling
 * state lists.  But really it's this file where all the magic happens.
 */

#include <stdlib.h>
#include <stdio.h>
#include "smatch.h"
#include "smatch_slist.h"
#include "smatch_extra.h"

struct smatch_state undefined = { .name = "undefined" };
struct smatch_state merged = { .name = "merged" };
struct smatch_state true_state = { .name = "true" };
struct smatch_state false_state = { .name = "false" };

static struct state_list *cur_slist; /* current states */

static struct state_list_stack *true_stack; /* states after a t/f branch */
static struct state_list_stack *false_stack;
static struct state_list_stack *pre_cond_stack; /* states before a t/f branch */

static struct state_list_stack *cond_true_stack; /* states affected by a branch */
static struct state_list_stack *cond_false_stack;

static struct state_list_stack *fake_cur_slist_stack;
static int read_only;

static struct state_list_stack *break_stack;
static struct state_list_stack *switch_stack;
static struct range_list_stack *remaining_cases;
static struct state_list_stack *default_stack;
static struct state_list_stack *continue_stack;

static struct named_stack *goto_stack;

static struct ptr_list *backup;

struct state_list_stack *implied_pools;

int option_debug;

void __print_cur_slist(void)
{
        __print_slist(cur_slist);
}

static int in_declarations_bit(void)
{
        struct statement *tmp;

        FOR_EACH_PTR_REVERSE(big_statement_stack, tmp) {
                if (tmp->type == STMT_DECLARATION)
                        return 1;
                return 0;
        } END_FOR_EACH_PTR_REVERSE(tmp);
        return 0;
}

int unreachable(void)
{
        static int reset_warnings = 1;

        if (cur_slist) {
                if (!__inline_fn)
                        reset_warnings = 1;
                return 0;
        }

        if (in_declarations_bit())
                return 1;

        /* option spammy turns on a noisier version of this */
        if (reset_warnings && !option_spammy)
                sm_msg("info: ignoring unreachable code.");
        if (!__inline_fn)
                reset_warnings = 0;
        return 1;
}

struct sm_state *set_state(int owner, const char *name, struct symbol *sym, struct smatch_state *state)
{
        struct sm_state *ret;

        if (!name)
                return NULL;

        if (read_only)
                sm_msg("Smatch Internal Error: cur_slist is read only.");

        if (option_debug || strcmp(check_name(owner), option_debug_check) == 0) {
                struct smatch_state *s;

                s = get_state(owner, name, sym);
                if (!s)
                        printf("%d new state. name='%s' [%s] %s\n",
                                get_lineno(), name, check_name(owner), show_state(state));
                else
                        printf("%d state change name='%s' [%s] %s => %s\n",
                                get_lineno(), name, check_name(owner), show_state(s),
                                show_state(state));
        }

        if (owner != -1 && unreachable())
                return NULL;

        if (fake_cur_slist_stack)
                set_state_stack(&fake_cur_slist_stack, owner, name, sym, state);

        ret =  set_state_slist(&cur_slist, owner, name, sym, state);

        if (cond_true_stack) {
                set_state_stack(&cond_true_stack, owner, name, sym, state);
                set_state_stack(&cond_false_stack, owner, name, sym, state);
        }
        return ret;
}

struct sm_state *set_state_expr(int owner, struct expression *expr, struct smatch_state *state)
{
        char *name;
        struct symbol *sym;
        struct sm_state *ret = NULL;

        expr = strip_expr(expr);
        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;
        ret = set_state(owner, name, sym, state);
free:
        free_string(name);
        return ret;
}

void __push_fake_cur_slist()
{
        push_slist(&fake_cur_slist_stack, NULL);
        __save_pre_cond_states();
}

struct state_list *__pop_fake_cur_slist()
{
        __use_pre_cond_states();
        return pop_slist(&fake_cur_slist_stack);
}

void __free_fake_cur_slist()
{
        struct state_list *slist;

        __use_pre_cond_states();
        slist = pop_slist(&fake_cur_slist_stack);
        free_slist(&slist);
}

void __set_fake_cur_slist_fast(struct state_list *slist)
{
        push_slist(&pre_cond_stack, cur_slist);
        cur_slist = slist;
        read_only = 1;
}

void __pop_fake_cur_slist_fast()
{
        cur_slist = pop_slist(&pre_cond_stack);
        read_only = 0;
}

void __merge_slist_into_cur(struct state_list *slist)
{
        struct sm_state *sm;
        struct sm_state *orig;
        struct sm_state *merged;

        FOR_EACH_PTR(slist, sm) {
                orig = get_sm_state(sm->owner, sm->name, sm->sym);
                if (orig)
                        merged = merge_sm_states(orig, sm);
                else
                        merged = sm;
                __set_sm(merged);
        } END_FOR_EACH_PTR(sm);
}

void __set_sm(struct sm_state *sm)
{
        if (read_only)
                sm_msg("Smatch Internal Error: cur_slist is read only.");

        if (option_debug ||
            strcmp(check_name(sm->owner), option_debug_check) == 0) {
                struct smatch_state *s;

                s = get_state(sm->owner, sm->name, sm->sym);
                if (!s)
                        printf("%d new state. name='%s' [%s] %s\n",
                                get_lineno(), sm->name, check_name(sm->owner),
                                show_state(sm->state));
                else
                        printf("%d state change name='%s' [%s] %s => %s\n",
                                get_lineno(), sm->name, check_name(sm->owner), show_state(s),
                                show_state(sm->state));
        }

        if (unreachable())
                return;

        if (fake_cur_slist_stack)
                overwrite_sm_state_stack(&fake_cur_slist_stack, sm);

        overwrite_sm_state(&cur_slist, sm);

        if (cond_true_stack) {
                overwrite_sm_state_stack(&cond_true_stack, sm);
                overwrite_sm_state_stack(&cond_false_stack, sm);
        }
}

struct smatch_state *get_state(int owner, const char *name, struct symbol *sym)
{
        return get_state_slist(cur_slist, owner, name, sym);
}

struct smatch_state *get_state_expr(int owner, struct expression *expr)
{
        char *name;
        struct symbol *sym;
        struct smatch_state *ret = NULL;

        expr = strip_expr(expr);
        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;
        ret = get_state(owner, name, sym);
free:
        free_string(name);
        return ret;
}

struct state_list *get_possible_states(int owner, const char *name, struct symbol *sym)
{
        struct sm_state *sms;

        sms = get_sm_state_slist(cur_slist, owner, name, sym);
        if (sms)
                return sms->possible;
        return NULL;
}

struct state_list *get_possible_states_expr(int owner, struct expression *expr)
{
        char *name;
        struct symbol *sym;
        struct state_list *ret = NULL;

        expr = strip_expr(expr);
        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;
        ret = get_possible_states(owner, name, sym);
free:
        free_string(name);
        return ret;
}

struct sm_state *get_sm_state(int owner, const char *name, struct symbol *sym)
{
        return get_sm_state_slist(cur_slist, owner, name, sym);
}

struct sm_state *get_sm_state_expr(int owner, struct expression *expr)
{
        char *name;
        struct symbol *sym;
        struct sm_state *ret = NULL;

        expr = strip_expr(expr);
        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;
        ret = get_sm_state(owner, name, sym);
free:
        free_string(name);
        return ret;
}

void delete_state(int owner, const char *name, struct symbol *sym)
{
        delete_state_slist(&cur_slist, owner, name, sym);
        if (cond_true_stack) {
                delete_state_stack(&pre_cond_stack, owner, name, sym);
                delete_state_stack(&cond_true_stack, owner, name, sym);
                delete_state_stack(&cond_false_stack, owner, name, sym);
        }
}

void delete_state_expr(int owner, struct expression *expr)
{
        char *name;
        struct symbol *sym;

        expr = strip_expr(expr);
        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;
        delete_state(owner, name, sym);
free:
        free_string(name);
}

struct state_list *get_all_states_slist(int owner, struct state_list *source)
{
        struct state_list *slist = NULL;
        struct sm_state *tmp;

        FOR_EACH_PTR(source, tmp) {
                if (tmp->owner == owner)
                        add_ptr_list(&slist, tmp);
        } END_FOR_EACH_PTR(tmp);

        return slist;
}

struct state_list *get_all_states(int owner)
{
        struct state_list *slist = NULL;
        struct sm_state *tmp;

        FOR_EACH_PTR(cur_slist, tmp) {
                if (tmp->owner == owner)
                        add_ptr_list(&slist, tmp);
        } END_FOR_EACH_PTR(tmp);

        return slist;
}

int is_reachable(void)
{
        if (cur_slist)
                return 1;
        return 0;
}

struct state_list *__get_cur_slist(void)
{
        return cur_slist;
}

void set_true_false_states(int owner, const char *name, struct symbol *sym,
                           struct smatch_state *true_state,
                           struct smatch_state *false_state)
{
        if (option_debug || strcmp(check_name(owner), option_debug_check) == 0) {
                struct smatch_state *tmp;

                tmp = get_state(owner, name, sym);
                printf("%d set_true_false '%s'.  Was %s.  Now T:%s F:%s\n",
                       get_lineno(), name, show_state(tmp),
                       show_state(true_state), show_state(false_state));
        }

        if (unreachable())
                return;

        if (!cond_false_stack || !cond_true_stack) {
                printf("Error:  missing true/false stacks\n");
                return;
        }

        if (true_state) {
                set_state_slist(&cur_slist, owner, name, sym, true_state);
                set_state_stack(&cond_true_stack, owner, name, sym, true_state);
        }
        if (false_state)
                set_state_stack(&cond_false_stack, owner, name, sym, false_state);
}

void set_true_false_states_expr(int owner, struct expression *expr,
                           struct smatch_state *true_state,
                           struct smatch_state *false_state)
{
        char *name;
        struct symbol *sym;

        expr = strip_expr(expr);
        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;
        set_true_false_states(owner, name, sym, true_state, false_state);
free:
        free_string(name);
}

void __set_true_false_sm(struct sm_state *true_sm, struct sm_state *false_sm)
{
        if (unreachable())
                return;

        if (!cond_false_stack || !cond_true_stack) {
                printf("Error:  missing true/false stacks\n");
                return;
        }

        if (true_sm) {
                overwrite_sm_state(&cur_slist, true_sm);
                overwrite_sm_state_stack(&cond_true_stack, true_sm);
        }
        if (false_sm)
                overwrite_sm_state_stack(&cond_false_stack, false_sm);
}

void nullify_path(void)
{
        free_slist(&cur_slist);
}

void __match_nullify_path_hook(const char *fn, struct expression *expr,
                               void *unused)
{
        nullify_path();
}

/*
 * At the start of every function we mark the path
 * as unnull.  That way there is always at least one state
 * in the cur_slist until nullify_path is called.  This
 * is used in merge_slist() for the first null check.
 */
void __unnullify_path(void)
{
        set_state(-1, "unnull_path", NULL, &true_state);
}

int __path_is_null(void)
{
        if (cur_slist)
                return 0;
        return 1;
}

static void check_stack_free(struct state_list_stack **stack)
{
        if (*stack) {
                sm_msg("smatch internal error:  stack not empty");
                free_stack_and_slists(stack);
        }
}

void save_all_states(void)
{
        __add_ptr_list(&backup, cur_slist, 0);

        __add_ptr_list(&backup, true_stack, 0);
        __add_ptr_list(&backup, false_stack, 0);
        __add_ptr_list(&backup, pre_cond_stack, 0);

        __add_ptr_list(&backup, cond_true_stack, 0);
        __add_ptr_list(&backup, cond_false_stack, 0);

        __add_ptr_list(&backup, fake_cur_slist_stack, 0);

        __add_ptr_list(&backup, break_stack, 0);
        __add_ptr_list(&backup, switch_stack, 0);
        __add_ptr_list(&backup, remaining_cases, 0);
        __add_ptr_list(&backup, default_stack, 0);
        __add_ptr_list(&backup, continue_stack, 0);

        __add_ptr_list(&backup, goto_stack, 0);
}

void nullify_all_states(void)
{
        cur_slist = NULL;

        true_stack = NULL;
        false_stack = NULL;
        pre_cond_stack = NULL;

        cond_true_stack = NULL;
        cond_false_stack = NULL;

        fake_cur_slist_stack = NULL;

        break_stack = NULL;
        switch_stack = NULL;
        remaining_cases = NULL;
        default_stack = NULL;
        continue_stack = NULL;

        goto_stack = NULL;
}

static void *pop_backup(void)
{
        void *ret;

        ret = last_ptr_list(backup);
        delete_ptr_list_last(&backup);
        return ret;
}

void restore_all_states(void)
{
        goto_stack = pop_backup();

        continue_stack = pop_backup();
        default_stack = pop_backup();
        remaining_cases = pop_backup();
        switch_stack = pop_backup();
        break_stack = pop_backup();

        fake_cur_slist_stack = pop_backup();

        cond_false_stack = pop_backup();
        cond_true_stack = pop_backup();

        pre_cond_stack = pop_backup();
        false_stack = pop_backup();
        true_stack = pop_backup();

        cur_slist = pop_backup();
}

void clear_all_states(void)
{
        struct named_slist *named_slist;

        nullify_path();
        check_stack_free(&true_stack);
        check_stack_free(&false_stack);
        check_stack_free(&pre_cond_stack);
        check_stack_free(&cond_true_stack);
        check_stack_free(&cond_false_stack);
        check_stack_free(&break_stack);
        check_stack_free(&switch_stack);
        check_stack_free(&continue_stack);
        free_stack_and_slists(&implied_pools);

        FOR_EACH_PTR(goto_stack, named_slist) {
                free_slist(&named_slist->slist);
        } END_FOR_EACH_PTR(named_slist);
        __free_ptr_list((struct ptr_list **)&goto_stack);
        free_every_single_sm_state();
}

void __push_cond_stacks(void)
{
        push_slist(&cond_true_stack, NULL);
        push_slist(&cond_false_stack, NULL);
}

struct state_list *__copy_cond_true_states(void)
{
        struct state_list *ret;

        ret = pop_slist(&cond_true_stack);
        push_slist(&cond_true_stack, clone_slist(ret));
        return ret;
}

struct state_list *__copy_cond_false_states(void)
{
        struct state_list *ret;

        ret = pop_slist(&cond_false_stack);
        push_slist(&cond_false_stack, clone_slist(ret));
        return ret;
}

struct state_list *__pop_cond_true_stack(void)
{
        return pop_slist(&cond_true_stack);
}

struct state_list *__pop_cond_false_stack(void)
{
        return pop_slist(&cond_false_stack);
}

/*
 * This combines the pre cond states with either the true or false states.
 * For example:
 * a = kmalloc() ; if (a !! foo(a)
 * In the pre state a is possibly null.  In the true state it is non null.
 * In the false state it is null.  Combine the pre and the false to get
 * that when we call 'foo', 'a' is null.
 */
static void __use_cond_stack(struct state_list_stack **stack)
{
        struct state_list *slist;

        free_slist(&cur_slist);

        cur_slist = pop_slist(&pre_cond_stack);
        push_slist(&pre_cond_stack, clone_slist(cur_slist));

        slist = pop_slist(stack);
        overwrite_slist(slist, &cur_slist);
        push_slist(stack, slist);
}

void __use_pre_cond_states(void)
{
        free_slist(&cur_slist);
        cur_slist = pop_slist(&pre_cond_stack);
}

void __use_cond_true_states(void)
{
        __use_cond_stack(&cond_true_stack);
}

void __use_cond_false_states(void)
{
        __use_cond_stack(&cond_false_stack);
}

void __negate_cond_stacks(void)
{
        struct state_list *old_false, *old_true;

        __use_cond_stack(&cond_false_stack);
        old_false = pop_slist(&cond_false_stack);
        old_true = pop_slist(&cond_true_stack);
        push_slist(&cond_false_stack, old_true);
        push_slist(&cond_true_stack, old_false);
}

void __and_cond_states(void)
{
        and_slist_stack(&cond_true_stack);
        or_slist_stack(&pre_cond_stack, cur_slist, &cond_false_stack);
}

void __or_cond_states(void)
{
        or_slist_stack(&pre_cond_stack, cur_slist, &cond_true_stack);
        and_slist_stack(&cond_false_stack);
}

void __save_pre_cond_states(void)
{
        push_slist(&pre_cond_stack, clone_slist(cur_slist));
}

void __discard_pre_cond_states(void)
{
        struct state_list *tmp;

        tmp = pop_slist(&pre_cond_stack);
        free_slist(&tmp);
}

void __use_cond_states(void)
{
        struct state_list *pre, *pre_clone, *true_states, *false_states;

        pre = pop_slist(&pre_cond_stack);
        pre_clone = clone_slist(pre);

        true_states = pop_slist(&cond_true_stack);
        overwrite_slist(true_states, &pre);
        /* we use the true states right away */
        free_slist(&cur_slist);
        cur_slist = pre;

        false_states = pop_slist(&cond_false_stack);
        overwrite_slist(false_states, &pre_clone);
        push_slist(&false_stack, pre_clone);
}

void __push_true_states(void)
{
        push_slist(&true_stack, clone_slist(cur_slist));
}

void __use_false_states(void)
{
        free_slist(&cur_slist);
        cur_slist = pop_slist(&false_stack);
}

void __discard_false_states(void)
{
        struct state_list *slist;

        slist = pop_slist(&false_stack);
        free_slist(&slist);
}

void __merge_false_states(void)
{
        struct state_list *slist;

        slist = pop_slist(&false_stack);
        merge_slist(&cur_slist, slist);
        free_slist(&slist);
}

void __merge_true_states(void)
{
        struct state_list *slist;

        slist = pop_slist(&true_stack);
        merge_slist(&cur_slist, slist);
        free_slist(&slist);
}

void __push_continues(void)
{
        push_slist(&continue_stack, NULL);
}

void __discard_continues(void)
{
        struct state_list *slist;

        slist = pop_slist(&continue_stack);
        free_slist(&slist);
}

void __process_continues(void)
{
        struct state_list *slist;

        slist = pop_slist(&continue_stack);
        if (!slist)
                slist = clone_slist(cur_slist);
        else
                merge_slist(&slist, cur_slist);

        push_slist(&continue_stack, slist);
}

static int top_slist_empty(struct state_list_stack **stack)
{
        struct state_list *tmp;
        int empty = 0;

        tmp = pop_slist(stack);
        if (!tmp)
                empty = 1;
        push_slist(stack, tmp);
        return empty;
}

/* a silly loop does this:  while(i--) { return; } */
void __warn_on_silly_pre_loops(void)
{
        if (!__path_is_null())
                return;
        if (!top_slist_empty(&continue_stack))
                return;
        if (!top_slist_empty(&break_stack))
                return;
        /* if the path was nullified before the loop, then we already
           printed an error earlier */
        if (top_slist_empty(&false_stack))
                return;
        sm_msg("info: loop could be replaced with if statement.");
}

void __merge_continues(void)
{
        struct state_list *slist;

        slist = pop_slist(&continue_stack);
        merge_slist(&cur_slist, slist);
        free_slist(&slist);
}

void __push_breaks(void)
{
        push_slist(&break_stack, NULL);
}

void __process_breaks(void)
{
        struct state_list *slist;

        slist = pop_slist(&break_stack);
        if (!slist)
                slist = clone_slist(cur_slist);
        else
                merge_slist(&slist, cur_slist);

        push_slist(&break_stack, slist);
}

int __has_breaks(void)
{
        struct state_list *slist;
        int ret;

        slist = pop_slist(&break_stack);
        ret = !!slist;
        push_slist(&break_stack, slist);
        return ret;
}

void __merge_breaks(void)
{
        struct state_list *slist;

        slist = pop_slist(&break_stack);
        merge_slist(&cur_slist, slist);
        free_slist(&slist);
}

void __use_breaks(void)
{
        free_slist(&cur_slist);
        cur_slist = pop_slist(&break_stack);
}

void __save_switch_states(struct expression *switch_expr)
{
        push_rl(&remaining_cases, __get_implied_values(switch_expr));
        push_slist(&switch_stack, clone_slist(cur_slist));
}

void __merge_switches(struct expression *switch_expr, struct expression *case_expr)
{
        struct state_list *slist;
        struct state_list *implied_slist;

        slist = pop_slist(&switch_stack);
        implied_slist = __implied_case_slist(switch_expr, case_expr, &remaining_cases, &slist);
        merge_slist(&cur_slist, implied_slist);
        free_slist(&implied_slist);
        push_slist(&switch_stack, slist);
}

void __discard_switches(void)
{
        struct state_list *slist;

        pop_rl(&remaining_cases);
        slist = pop_slist(&switch_stack);
        free_slist(&slist);
}

void __push_default(void)
{
        push_slist(&default_stack, NULL);
}

void __set_default(void)
{
        set_state_stack(&default_stack, 0, "has_default", NULL, &true_state);
}

int __pop_default(void)
{
        struct state_list *slist;

        slist = pop_slist(&default_stack);
        if (slist) {
                free_slist(&slist);
                return 1;
        }
        return 0;
}

static struct named_slist *alloc_named_slist(const char *name, struct state_list *slist)
{
        struct named_slist *named_slist = __alloc_named_slist(0);

        named_slist->name = (char *)name;
        named_slist->slist = slist;
        return named_slist;
}

void __save_gotos(const char *name)
{
        struct state_list **slist;
        struct state_list *clone;

        slist = get_slist_from_named_stack(goto_stack, name);
        if (slist) {
                clone = clone_slist(cur_slist);
                merge_slist(slist, clone);
                free_slist(&clone);
                return;
        } else {
                struct named_slist *named_slist;

                clone = clone_slist(cur_slist);
                named_slist = alloc_named_slist(name, clone);
                add_ptr_list(&goto_stack, named_slist);
        }
}

void __merge_gotos(const char *name)
{
        struct state_list **slist;

        slist = get_slist_from_named_stack(goto_stack, name);
        if (slist)
                merge_slist(&cur_slist, *slist);
}