compact_vars.c

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/*
   +----------------------------------------------------------------------+
   | Zend Engine, Removing unused variables                               |
   +----------------------------------------------------------------------+
   | Copyright (c) The PHP Group                                          |
   +----------------------------------------------------------------------+
   | This source file is subject to version 3.01 of the PHP license,      |
   | that is bundled with this package in the file LICENSE, and is        |
   | available through the world-wide-web at the following url:           |
   | https://www.php.net/license/3_01.txt                                 |
   | If you did not receive a copy of the PHP license and are unable to   |
   | obtain it through the world-wide-web, please send a note to          |
   | license@php.net so we can mail you a copy immediately.               |
   +----------------------------------------------------------------------+
   | Authors: Nikita Popov <nikic@php.net>                                |
   +----------------------------------------------------------------------+
*/
 
#include "Optimizer/zend_optimizer_internal.h"
#include "zend_bitset.h"
#include "zend_observer.h"
 
/* This pass removes all CVs and temporaries that are completely unused. It does *not* merge any CVs or TMPs.
 * This pass does not operate on SSA form anymore. */
void zend_optimizer_compact_vars(zend_op_array *op_array) {
    int i;
 
    ALLOCA_FLAG(use_heap1);
    ALLOCA_FLAG(use_heap2);
    uint32_t used_vars_len = zend_bitset_len(op_array->last_var + op_array->T);
    zend_bitset used_vars = ZEND_BITSET_ALLOCA(used_vars_len, use_heap1);
    uint32_t *vars_map = do_alloca((op_array->last_var + op_array->T) * sizeof(uint32_t), use_heap2);
    uint32_t num_cvs, num_tmps;
 
    /* Determine which CVs are used */
    zend_bitset_clear(used_vars, used_vars_len);
    for (i = 0; i < op_array->last; i++) {
        zend_op *opline = &op_array->opcodes[i];
        if (opline->op1_type & (IS_CV|IS_VAR|IS_TMP_VAR)) {
            zend_bitset_incl(used_vars, VAR_NUM(opline->op1.var));
        }
        if (opline->op2_type & (IS_CV|IS_VAR|IS_TMP_VAR)) {
            zend_bitset_incl(used_vars, VAR_NUM(opline->op2.var));
        }
        if (opline->result_type & (IS_CV|IS_VAR|IS_TMP_VAR)) {
            zend_bitset_incl(used_vars, VAR_NUM(opline->result.var));
            if (opline->opcode == ZEND_ROPE_INIT) {
                uint32_t num = ((opline->extended_value * sizeof(zend_string*)) + (sizeof(zval) - 1)) / sizeof(zval);
                while (num > 1) {
                    num--;
                    zend_bitset_incl(used_vars, VAR_NUM(opline->result.var) + num);
                }
            }
        }
    }
 
    num_cvs = 0;
    for (i = 0; i < op_array->last_var; i++) {
        if (zend_bitset_in(used_vars, i)) {
            vars_map[i] = num_cvs++;
        } else {
            vars_map[i] = (uint32_t) -1;
        }
    }
 
    num_tmps = 0;
    for (i = op_array->last_var; i < op_array->last_var + op_array->T; i++) {
        if (zend_bitset_in(used_vars, i)) {
            vars_map[i] = num_cvs + num_tmps++;
        } else {
            vars_map[i] = (uint32_t) -1;
        }
    }
 
    free_alloca(used_vars, use_heap1);
    if (num_cvs == op_array->last_var && num_tmps == op_array->T) {
        free_alloca(vars_map, use_heap2);
        return;
    }
 
    ZEND_ASSERT(num_cvs <= op_array->last_var);
    ZEND_ASSERT(num_tmps <= op_array->T);
 
    /* Update CV and TMP references in opcodes */
    for (i = 0; i < op_array->last; i++) {
        zend_op *opline = &op_array->opcodes[i];
        if (opline->op1_type & (IS_CV|IS_VAR|IS_TMP_VAR)) {
            opline->op1.var = NUM_VAR(vars_map[VAR_NUM(opline->op1.var)]);
        }
        if (opline->op2_type & (IS_CV|IS_VAR|IS_TMP_VAR)) {
            opline->op2.var = NUM_VAR(vars_map[VAR_NUM(opline->op2.var)]);
        }
        if (opline->result_type & (IS_CV|IS_VAR|IS_TMP_VAR)) {
            opline->result.var = NUM_VAR(vars_map[VAR_NUM(opline->result.var)]);
        }
    }
 
    /* Update CV name table */
    if (num_cvs != op_array->last_var) {
        if (num_cvs) {
            zend_string **names = safe_emalloc(sizeof(zend_string *), num_cvs, 0);
            for (i = 0; i < op_array->last_var; i++) {
                if (vars_map[i] != (uint32_t) -1) {
                    names[vars_map[i]] = op_array->vars[i];
                } else {
                    zend_string_release_ex(op_array->vars[i], 0);
                }
            }
            efree(op_array->vars);
            op_array->vars = names;
        } else {
            for (i = 0; i < op_array->last_var; i++) {
                zend_string_release_ex(op_array->vars[i], 0);
            }
            efree(op_array->vars);
            op_array->vars = NULL;
        }
        op_array->last_var = num_cvs;
    }
 
    op_array->T = num_tmps + ZEND_OBSERVER_ENABLED; // reserve last temporary for observers if enabled
 
    free_alloca(vars_map, use_heap2);
}