unreachable: silence "not actually initialized" false positives

[smatch.git] / smatch_conditions.c

/*
 * Copyright (C) 2006,2008 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
 */

/*
 * The simplest type of condition is
 * if (a) { ...
 *
 * The next simplest kind of conditions is
 * if (a && b) { c;
 * In that case 'a' is true when we get to 'b' and both are true
 * when we get to c.
 *
 * Or's are a little more complicated.
 * if (a || b) { c;
 * We know 'a' is not true when we get to 'b' but it may be true
 * when we get to c.
 *
 * If we mix and's and or's that's even more complicated.
 * if (a && b && c || a && d) { d ;
 * 'a' is true when we evaluate 'b', and 'd'.
 * 'b' is true when we evaluate 'c' but otherwise we don't.
 *
 * The other thing that complicates matters is if we negate
 * some if conditions.
 * if (!a) { ...
 * Smatch has passes the un-negated version to the client and flip
 * the true and false values internally.  This makes it easier
 * to write checks.
 *
 * And negations can be part of a compound.
 * if (a && !(b || c)) { d;
 * In that situation we multiply the negative through to simplify
 * stuff so that we can remove the parens like this:
 * if (a && !b && !c) { d;
 *
 * One other thing is that:
 * if ((a) != 0){ ...
 * that's basically the same as testing for just 'a' and we simplify
 * comparisons with zero before passing it to the script.
 *
 */

#include "smatch.h"
#include "smatch_slist.h"
#include "smatch_extra.h"
#include "smatch_expression_stacks.h"

extern int __expr_stmt_count;

static void split_conditions(struct expression *expr);

static int is_logical_and(struct expression *expr)
{
        if (expr->op == SPECIAL_LOGICAL_AND)
                return 1;
        return 0;
}

static int handle_zero_comparisons(struct expression *expr)
{
        struct expression *tmp = NULL;

        // if left is zero or right is zero
        if (is_zero(expr->left))
                tmp = expr->right;
        else if (is_zero(expr->right))
                tmp = expr->left;
        else
                return 0;

        // "if (foo != 0)" is the same as "if (foo)"
        if (expr->op == SPECIAL_NOTEQUAL) {
                split_conditions(tmp);
                return 1;
        }

        // "if (foo == 0)" is the same as "if (!foo)"
        if (expr->op == SPECIAL_EQUAL) {
                split_conditions(tmp);
                __negate_cond_stacks();
                return 1;
        }

        return 0;
}

/*
 * This function is for handling calls to likely/unlikely
 */

static int ignore_builtin_expect(struct expression *expr)
{
        if (sym_name_is("__builtin_expect", expr->fn)) {
                split_conditions(first_ptr_list((struct ptr_list *) expr->args));
                return 1;
        }
        return 0;
}

/*
 * handle_compound_stmt() is for: foo = ({blah; blah; blah; 1})
 */

static void handle_compound_stmt(struct statement *stmt)
{
        struct expression *expr = NULL;
        struct statement *last;
        struct statement *s;

        last = last_ptr_list((struct ptr_list *)stmt->stmts);
        if (last->type != STMT_EXPRESSION)
                last = NULL;
        else
                expr = last->expression;

        FOR_EACH_PTR(stmt->stmts, s) {
                if (s != last)
                        __split_stmt(s);
        } END_FOR_EACH_PTR(s);
        split_conditions(expr);
        return;
}

static int handle_preop(struct expression *expr)
{
        struct statement *stmt;

        if (expr->op == '!') {
                split_conditions(expr->unop);
                __negate_cond_stacks();
                return 1;
        }
        stmt = get_expression_statement(expr);
        if (stmt) {
                handle_compound_stmt(stmt);
                return 1;
        }
        return 0;
}

static void handle_logical(struct expression *expr)
{
        /*
         * If we come to an "and" expr then:
         * We split the left side.
         * We keep all the current states.
         * We split the right side.
         * We keep all the states from both true sides.
         *
         * If it's an "or" expr then:
         * We save the current slist.
         * We split the left side.
         * We use the false states for the right side.
         * We split the right side.
         * We save all the states that are the same on both sides.
         */

        split_conditions(expr->left);
        __process_post_op_stack();

        if (!is_logical_and(expr))
                __use_cond_false_states();

        __push_cond_stacks();

        __save_pre_cond_states();
        split_conditions(expr->right);
        __process_post_op_stack();
        __discard_pre_cond_states();

        if (is_logical_and(expr))
                __and_cond_states();
        else
                __or_cond_states();

        __use_cond_true_states();
}

static struct stree *combine_strees(struct stree *orig, struct stree *fake, struct stree *new)
{
        struct stree *ret = NULL;

        overwrite_stree(orig, &ret);
        overwrite_stree(fake, &ret);
        overwrite_stree(new, &ret);
        free_stree(&new);

        return ret;
}

/*
 * handle_select()
 * if ((aaa()?bbb():ccc())) { ...
 *
 * This is almost the same as:
 * if ((aaa() && bbb()) || (!aaa() && ccc())) { ...
 *
 * It's a bit complicated because we shouldn't pass aaa()
 * to the clients more than once.
 */

static void handle_select(struct expression *expr)
{
        struct stree *a_T = NULL;
        struct stree *a_F = NULL;
        struct stree *a_T_b_T = NULL;
        struct stree *a_T_b_F = NULL;
        struct stree *a_T_b_fake = NULL;
        struct stree *a_F_c_T = NULL;
        struct stree *a_F_c_F = NULL;
        struct stree *a_F_c_fake = NULL;
        struct stree *tmp;
        struct sm_state *sm;

        /*
         * Imagine we have this:  if (a ? b : c) { ...
         *
         * The condition is true if "a" is true and "b" is true or
         * "a" is false and "c" is true.  It's false if "a" is true
         * and "b" is false or "a" is false and "c" is false.
         *
         * The variable name "a_T_b_T" stands for "a true b true" etc.
         *
         * But if we know "b" is true then we can simpilify things.
         * The condition is true if "a" is true or if "a" is false and
         * "c" is true.  The only way the condition can be false is if
         * "a" is false and "c" is false.
         *
         * The remaining thing is the "a_T_b_fake".  When we simplify
         * the equations we have to take into consideration that other
         * states may have changed that don't play into the true false
         * equation.  Take the following example:
         * if ({
         *         (flags) = __raw_local_irq_save();
         *         _spin_trylock(lock) ? 1 :
         *                 ({ raw_local_irq_restore(flags);  0; });
         *    })
         * Smatch has to record that the irq flags were restored on the
         * false path.
         *
         */

        __save_pre_cond_states();

        split_conditions(expr->conditional);

        a_T = __copy_cond_true_states();
        a_F = __copy_cond_false_states();

        __push_cond_stacks();
        __push_fake_cur_stree();
        split_conditions(expr->cond_true);
        __process_post_op_stack();
        a_T_b_fake = __pop_fake_cur_stree();
        a_T_b_T = combine_strees(a_T, a_T_b_fake, __pop_cond_true_stack());
        a_T_b_F = combine_strees(a_T, a_T_b_fake, __pop_cond_false_stack());

        __use_cond_false_states();

        __push_cond_stacks();
        __push_fake_cur_stree();
        split_conditions(expr->cond_false);
        a_F_c_fake = __pop_fake_cur_stree();
        a_F_c_T = combine_strees(a_F, a_F_c_fake, __pop_cond_true_stack());
        a_F_c_F = combine_strees(a_F, a_F_c_fake, __pop_cond_false_stack());

        /* We have to restore the pre condition states so that
           implied_condition_true() will use the right cur_stree */
        __use_pre_cond_states();

        if (implied_condition_true(expr->cond_true)) {
                free_stree(&a_T_b_T);
                free_stree(&a_T_b_F);
                a_T_b_T = clone_stree(a_T);
                overwrite_stree(a_T_b_fake, &a_T_b_T);
        }
        if (implied_condition_false(expr->cond_true)) {
                free_stree(&a_T_b_T);
                free_stree(&a_T_b_F);
                a_T_b_F = clone_stree(a_T);
                overwrite_stree(a_T_b_fake, &a_T_b_F);
        }
        if (implied_condition_true(expr->cond_false)) {
                free_stree(&a_F_c_T);
                free_stree(&a_F_c_F);
                a_F_c_T = clone_stree(a_F);
                overwrite_stree(a_F_c_fake, &a_F_c_T);
        }
        if (implied_condition_false(expr->cond_false)) {
                free_stree(&a_F_c_T);
                free_stree(&a_F_c_F);
                a_F_c_F = clone_stree(a_F);
                overwrite_stree(a_F_c_fake, &a_F_c_F);
        }

        merge_stree(&a_T_b_T, a_F_c_T);
        merge_stree(&a_T_b_F, a_F_c_F);

        tmp = __pop_cond_true_stack();
        free_stree(&tmp);
        tmp = __pop_cond_false_stack();
        free_stree(&tmp);

        __push_cond_stacks();
        FOR_EACH_SM(a_T_b_T, sm) {
                __set_true_false_sm(sm, NULL);
        } END_FOR_EACH_SM(sm);
        FOR_EACH_SM(a_T_b_F, sm) {
                __set_true_false_sm(NULL, sm);
        } END_FOR_EACH_SM(sm);

        free_stree(&a_T_b_fake);
        free_stree(&a_F_c_fake);
        free_stree(&a_F_c_T);
        free_stree(&a_F_c_F);
        free_stree(&a_T_b_T);
        free_stree(&a_T_b_F);
        free_stree(&a_T);
        free_stree(&a_F);
}

static int make_op_unsigned(int op)
{
        switch (op) {
        case '<':
                return SPECIAL_UNSIGNED_LT;
        case SPECIAL_LTE:
                return SPECIAL_UNSIGNED_LTE;
        case '>':
                return SPECIAL_UNSIGNED_GT;
        case SPECIAL_GTE:
                return SPECIAL_UNSIGNED_GTE;
        }
        return op;
}

static void hackup_unsigned_compares(struct expression *expr)
{
        if (expr->type != EXPR_COMPARE)
                return;

        if (type_unsigned(get_type(expr)))
                expr->op = make_op_unsigned(expr->op);
}

static void split_conditions(struct expression *expr)
{
        if (option_debug) {
                char *cond = expr_to_str(expr);

                sm_debug("%d in split_conditions (%s)\n", get_lineno(), cond);
                free_string(cond);
        }

        expr = strip_expr(expr);
        if (!expr)
                return;

        switch (expr->type) {
        case EXPR_LOGICAL:
                __pass_to_client(expr, LOGIC_HOOK);
                handle_logical(expr);
                return;
        case EXPR_COMPARE:
                hackup_unsigned_compares(expr);
                if (handle_zero_comparisons(expr))
                        return;
                break;
        case EXPR_CALL:
                if (ignore_builtin_expect(expr))
                        return;
                break;
        case EXPR_PREOP:
                if (handle_preop(expr))
                        return;
                break;
        case EXPR_CONDITIONAL:
        case EXPR_SELECT:
                handle_select(expr);
                return;
        }

        /* fixme: this should be in smatch_flow.c
           but because of the funny stuff we do with conditions
           it's awkward to put it there.  We would need to
           call CONDITION_HOOK in smatch_flow as well.
        */
        push_expression(&big_expression_stack, expr);
        if (expr->type == EXPR_COMPARE) {
                if (expr->left->type != EXPR_POSTOP)
                        __split_expr(expr->left);
                if (expr->right->type != EXPR_POSTOP)
                        __split_expr(expr->right);
        } else if (expr->type != EXPR_POSTOP) {
                __split_expr(expr);
        }
        __pass_to_client(expr, CONDITION_HOOK);
        if (expr->type == EXPR_COMPARE) {
                if (expr->left->type == EXPR_POSTOP)
                        __split_expr(expr->left);
                if (expr->right->type == EXPR_POSTOP)
                        __split_expr(expr->right);
        } else if (expr->type == EXPR_POSTOP) {
                __split_expr(expr);
        }
        __process_post_op_stack();
        pop_expression(&big_expression_stack);
}

static int inside_condition;
void __split_whole_condition(struct expression *expr)
{
        sm_debug("%d in __split_whole_condition\n", get_lineno());
        inside_condition++;
        __save_pre_cond_states();
        __push_cond_stacks();
        /* it's a hack, but it's sometimes handy to have this stuff
           on the big_expression_stack.  */
        push_expression(&big_expression_stack, expr);
        if (expr)
                split_conditions(expr);
        __use_cond_states();
        __pass_to_client(expr, WHOLE_CONDITION_HOOK);
        pop_expression(&big_expression_stack);
        inside_condition--;
        sm_debug("%d done __split_whole_condition\n", get_lineno());
}

void __handle_logic(struct expression *expr)
{
        sm_debug("%d in __handle_logic\n", get_lineno());
        inside_condition++;
        __save_pre_cond_states();
        __push_cond_stacks();
        /* it's a hack, but it's sometimes handy to have this stuff
           on the big_expression_stack.  */
        push_expression(&big_expression_stack, expr);
        if (expr)
                split_conditions(expr);
        __use_cond_states();
        __pass_to_client(expr, WHOLE_CONDITION_HOOK);
        pop_expression(&big_expression_stack);
        __merge_false_states();
        inside_condition--;
        sm_debug("%d done __handle_logic\n", get_lineno());
}

int is_condition(struct expression *expr)
{

        expr = strip_expr(expr);
        if (!expr)
                return 0;

        switch (expr->type) {
        case EXPR_LOGICAL:
        case EXPR_COMPARE:
                return 1;
        case EXPR_PREOP:
                if (expr->op == '!')
                        return 1;
        }
        return 0;
}

int __handle_condition_assigns(struct expression *expr)
{
        struct expression *right;

        right = strip_expr(expr->right);
        if (!is_condition(expr->right))
                return 0;

        sm_debug("%d in __handle_condition_assigns\n", get_lineno());
        inside_condition++;
        __save_pre_cond_states();
        __push_cond_stacks();
        /* it's a hack, but it's sometimes handy to have this stuff
           on the big_expression_stack.  */
        push_expression(&big_expression_stack, right);
        split_conditions(right);
        __use_cond_states();
        set_extra_expr_mod(expr->left, alloc_estate_sval(sval_type_val(get_type(expr->left), 1)));
        __pass_to_client(right, WHOLE_CONDITION_HOOK);
        pop_expression(&big_expression_stack);
        inside_condition--;
        sm_debug("%d done __handle_condition_assigns\n", get_lineno());

        __push_true_states();
        __use_false_states();
        set_extra_expr_mod(expr->left, alloc_estate_sval(sval_type_val(get_type(expr->left), 0)));
        __merge_true_states();
        __pass_to_client(expr, ASSIGNMENT_HOOK);
        return 1;
}

static int is_select_assign(struct expression *expr)
{
        struct expression *right;

        if (expr->op != '=')
                return 0;
        right = strip_expr(expr->right);
        if (right->type == EXPR_CONDITIONAL)
                return 1;
        if (right->type == EXPR_SELECT)
                return 1;
        return 0;
}

static void set_fake_assign(struct expression *new,
                        struct expression *left, int op, struct expression *right)
{

        new->pos = left->pos;
        new->op = op;
        new->type = EXPR_ASSIGNMENT;
        new->left = left;
        new->right = right;
}

int __handle_select_assigns(struct expression *expr)
{
        struct expression *right;
        struct stree *final_states = NULL;
        struct sm_state *sm;
        int is_true;
        int is_false;

        if (!is_select_assign(expr))
                return 0;
        sm_debug("%d in __handle_ternary_assigns\n", get_lineno());
        right = strip_expr(expr->right);

        is_true = implied_condition_true(right->conditional);
        is_false = implied_condition_false(right->conditional);

        /* hah hah.  the ultra fake out */
        __save_pre_cond_states();
        __split_whole_condition(right->conditional);

        if (!is_false) {
                struct expression fake_expr;

                if (right->cond_true)
                        set_fake_assign(&fake_expr, expr->left, expr->op, right->cond_true);
                else
                        set_fake_assign(&fake_expr, expr->left, expr->op, right->conditional);
                __split_expr(&fake_expr);
                final_states = clone_stree(__get_cur_stree());
        }

        __use_false_states();
        if (!is_true) {
                struct expression fake_expr;

                set_fake_assign(&fake_expr, expr->left, expr->op, right->cond_false);
                __split_expr(&fake_expr);
                merge_stree(&final_states, __get_cur_stree());
        }

        __use_pre_cond_states();

        FOR_EACH_SM(final_states, sm) {
                __set_sm(sm);
        } END_FOR_EACH_SM(sm);

        free_stree(&final_states);

        sm_debug("%d done __handle_ternary_assigns\n", get_lineno());

        return 1;
}

static struct statement *split_then_return_last(struct statement *stmt)
{
        struct statement *tmp;
        struct statement *last_stmt;

        last_stmt = last_ptr_list((struct ptr_list *)stmt->stmts);
        if (!last_stmt)
                return NULL;

        __push_scope_hooks();
        FOR_EACH_PTR(stmt->stmts, tmp) {
                if (tmp == last_stmt)
                        return last_stmt;
                __split_stmt(tmp);
        } END_FOR_EACH_PTR(tmp);
        return NULL;
}

int __handle_expr_statement_assigns(struct expression *expr)
{
        struct expression *right;
        struct statement *stmt;

        right = expr->right;
        if (right->type == EXPR_PREOP && right->op == '(')
                right = right->unop;
        if (right->type != EXPR_STATEMENT)
                return 0;

        __expr_stmt_count++;
        stmt = right->statement;
        if (stmt->type == STMT_COMPOUND) {
                struct statement *last_stmt;
                struct expression fake_assign;
                struct expression fake_expr_stmt;

                last_stmt = split_then_return_last(stmt);
                if (!last_stmt) {
                        __expr_stmt_count--;
                        return 0;
                }

                fake_expr_stmt.pos = last_stmt->pos;
                fake_expr_stmt.type = EXPR_STATEMENT;
                fake_expr_stmt.statement = last_stmt;

                fake_assign.pos = last_stmt->pos;
                fake_assign.op = expr->op;
                fake_assign.type = EXPR_ASSIGNMENT;
                fake_assign.left = expr->left;
                fake_assign.right = &fake_expr_stmt;

                __split_expr(&fake_assign);

                __call_scope_hooks();
        } else if (stmt->type == STMT_EXPRESSION) {
                struct expression fake_assign;

                fake_assign.pos = stmt->pos;
                fake_assign.op = expr->op;
                fake_assign.type = EXPR_ASSIGNMENT;
                fake_assign.left = expr->left;
                fake_assign.right = stmt->expression;

                __split_expr(&fake_assign);

        } else {
                __split_stmt(stmt);
        }
        __expr_stmt_count--;
        return 1;
}

int in_condition(void)
{
        return inside_condition;
}