escape_analysis.c

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/*
   +----------------------------------------------------------------------+
   | Zend OPcache, Escape Analysis                                        |
   +----------------------------------------------------------------------+
   | 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: Dmitry Stogov <dmitry@php.net>                              |
   +----------------------------------------------------------------------+
*/
 
#include "Optimizer/zend_optimizer.h"
#include "Optimizer/zend_optimizer_internal.h"
#include "zend_bitset.h"
#include "zend_cfg.h"
#include "zend_ssa.h"
#include "zend_inference.h"
#include "zend_dump.h"
 
/*
 * T. Kotzmann and H. Mossenbock. Escape analysis  in the context of dynamic
 * compilation and deoptimization. In Proceedings of the International
 * Conference on Virtual Execution Environments, pages 111-120, Chicago,
 * June 2005
 */
 
static zend_always_inline void union_find_init(int *parent, int *size, int count) /* {{{ */
{
    int i;
 
    for (i = 0; i < count; i++) {
        parent[i] = i;
        size[i] = 1;
    }
}
/* }}} */
 
static zend_always_inline int union_find_root(int *parent, int i) /* {{{ */
{
    int p = parent[i];
 
    while (i != p) {
        p = parent[p];
        parent[i] = p;
        i = p;
        p = parent[i];
    }
    return i;
}
/* }}} */
 
static zend_always_inline void union_find_unite(int *parent, int *size, int i, int j) /* {{{ */
{
    int r1 = union_find_root(parent, i);
    int r2 = union_find_root(parent, j);
 
    if (r1 != r2) {
        if (size[r1] < size[r2]) {
            parent[r1] = r2;
            size[r2] += size[r1];
        } else {
            parent[r2] = r1;
            size[r1] += size[r2];
        }
    }
}
/* }}} */
 
static zend_result zend_build_equi_escape_sets(int *parent, zend_op_array *op_array, zend_ssa *ssa) /* {{{ */
{
    zend_ssa_var *ssa_vars = ssa->vars;
    int ssa_vars_count = ssa->vars_count;
    zend_ssa_phi *p;
    int i, j;
    int *size;
    ALLOCA_FLAG(use_heap)
 
    size = do_alloca(sizeof(int) * ssa_vars_count, use_heap);
    if (!size) {
        return FAILURE;
    }
    union_find_init(parent, size, ssa_vars_count);
 
    for (i = 0; i < ssa_vars_count; i++) {
        if (ssa_vars[i].definition_phi) {
            p = ssa_vars[i].definition_phi;
            if (p->pi >= 0) {
                union_find_unite(parent, size, i, p->sources[0]);
            } else {
                for (j = 0; j < ssa->cfg.blocks[p->block].predecessors_count; j++) {
                    union_find_unite(parent, size, i, p->sources[j]);
                }
            }
        } else if (ssa_vars[i].definition >= 0) {
            int def = ssa_vars[i].definition;
            zend_ssa_op *op = ssa->ops + def;
            zend_op *opline =  op_array->opcodes + def;
 
            if (op->op1_def >= 0) {
                if (op->op1_use >= 0) {
                    if (opline->opcode != ZEND_ASSIGN) {
                        union_find_unite(parent, size, op->op1_def, op->op1_use);
                    }
                }
                if (opline->opcode == ZEND_ASSIGN && op->op2_use >= 0) {
                    union_find_unite(parent, size, op->op1_def, op->op2_use);
                }
            }
            if (op->op2_def >= 0) {
                if (op->op2_use >= 0) {
                    union_find_unite(parent, size, op->op2_def, op->op2_use);
                }
            }
            if (op->result_def >= 0) {
                if (op->result_use >= 0) {
                    if (opline->opcode != ZEND_QM_ASSIGN) {
                        union_find_unite(parent, size, op->result_def, op->result_use);
                    }
                }
                if (opline->opcode == ZEND_QM_ASSIGN && op->op1_use >= 0) {
                    union_find_unite(parent, size, op->result_def, op->op1_use);
                }
                if (opline->opcode == ZEND_ASSIGN && op->op2_use >= 0) {
                    union_find_unite(parent, size, op->result_def, op->op2_use);
                }
                if (opline->opcode == ZEND_ASSIGN && op->op1_def >= 0) {
                    union_find_unite(parent, size, op->result_def, op->op1_def);
                }
            }
        }
    }
 
    for (i = 0; i < ssa_vars_count; i++) {
        parent[i] = union_find_root(parent, i);
    }
 
    free_alloca(size, use_heap);
 
    return SUCCESS;
}
/* }}} */
 
static bool is_allocation_def(zend_op_array *op_array, zend_ssa *ssa, int def, int var, const zend_script *script) /* {{{ */
{
    zend_ssa_op *ssa_op = ssa->ops + def;
    zend_op *opline = op_array->opcodes + def;
 
    if (ssa_op->result_def == var) {
        switch (opline->opcode) {
            case ZEND_INIT_ARRAY:
                return 1;
            case ZEND_NEW: {
                /* objects with destructors should escape */
                zend_class_entry *ce = zend_optimizer_get_class_entry_from_op1(
                    script, op_array, opline);
                uint32_t forbidden_flags =
                    /* These flags will always cause an exception */
                    ZEND_ACC_IMPLICIT_ABSTRACT_CLASS | ZEND_ACC_EXPLICIT_ABSTRACT_CLASS
                    | ZEND_ACC_INTERFACE | ZEND_ACC_TRAIT;
                if (ce
                 && !ce->parent
                 && !ce->create_object
                 && ce->default_object_handlers->get_constructor == zend_std_get_constructor
                 && ce->default_object_handlers->dtor_obj == zend_objects_destroy_object
                 && !ce->constructor
                 && !ce->destructor
                 && !ce->__get
                 && !ce->__set
                 && !(ce->ce_flags & forbidden_flags)
                 && (ce->ce_flags & ZEND_ACC_CONSTANTS_UPDATED)) {
                    return 1;
                }
                break;
            }
            case ZEND_QM_ASSIGN:
                if (opline->op1_type == IS_CONST
                 && Z_TYPE_P(CRT_CONSTANT(opline->op1)) == IS_ARRAY) {
                    return 1;
                }
                if (opline->op1_type == IS_CV && (OP1_INFO() & MAY_BE_ARRAY)) {
                    return 1;
                }
                break;
            case ZEND_ASSIGN:
                if (opline->op1_type == IS_CV && (OP1_INFO() & MAY_BE_ARRAY)) {
                    return 1;
                }
                break;
        }
    } else if (ssa_op->op1_def == var) {
        switch (opline->opcode) {
            case ZEND_ASSIGN:
                if (opline->op2_type == IS_CONST
                 && Z_TYPE_P(CRT_CONSTANT(opline->op2)) == IS_ARRAY) {
                    return 1;
                }
                if (opline->op2_type == IS_CV && (OP2_INFO() & MAY_BE_ARRAY)) {
                    return 1;
                }
                break;
            case ZEND_ASSIGN_DIM:
                if (OP1_INFO() & (MAY_BE_UNDEF | MAY_BE_NULL | MAY_BE_FALSE)) {
                    /* implicit object/array allocation */
                    return 1;
                }
                break;
        }
    }
 
    return 0;
}
/* }}} */
 
static bool is_local_def(zend_op_array *op_array, zend_ssa *ssa, int def, int var, const zend_script *script) /* {{{ */
{
    zend_ssa_op *op = ssa->ops + def;
    zend_op *opline = op_array->opcodes + def;
 
    if (op->result_def == var) {
        switch (opline->opcode) {
            case ZEND_INIT_ARRAY:
            case ZEND_ADD_ARRAY_ELEMENT:
            case ZEND_QM_ASSIGN:
            case ZEND_ASSIGN:
                return 1;
            case ZEND_NEW: {
                /* objects with destructors should escape */
                zend_class_entry *ce = zend_optimizer_get_class_entry_from_op1(
                    script, op_array, opline);
                if (ce
                 && !ce->create_object
                 && ce->default_object_handlers->get_constructor == zend_std_get_constructor
                 && ce->default_object_handlers->dtor_obj == zend_objects_destroy_object
                 && !ce->constructor
                 && !ce->destructor
                 && !ce->__get
                 && !ce->__set
                 && !ce->parent) {
                    return 1;
                }
                break;
            }
        }
    } else if (op->op1_def == var) {
        switch (opline->opcode) {
            case ZEND_ASSIGN:
            case ZEND_ASSIGN_DIM:
            case ZEND_ASSIGN_OBJ:
            case ZEND_ASSIGN_OBJ_REF:
            case ZEND_ASSIGN_DIM_OP:
            case ZEND_ASSIGN_OBJ_OP:
            case ZEND_PRE_INC_OBJ:
            case ZEND_PRE_DEC_OBJ:
            case ZEND_POST_INC_OBJ:
            case ZEND_POST_DEC_OBJ:
                return 1;
        }
    }
 
    return 0;
}
/* }}} */
 
static bool is_escape_use(zend_op_array *op_array, zend_ssa *ssa, int use, int var) /* {{{ */
{
    zend_ssa_op *ssa_op = ssa->ops + use;
    zend_op *opline = op_array->opcodes + use;
 
    if (ssa_op->op1_use == var) {
        switch (opline->opcode) {
            case ZEND_ASSIGN:
                /* no_val */
                break;
            case ZEND_QM_ASSIGN:
                if (opline->op1_type == IS_CV) {
                    if (OP1_INFO() & MAY_BE_OBJECT) {
                        /* object aliasing */
                        return 1;
                    }
                }
                break;
            case ZEND_ISSET_ISEMPTY_DIM_OBJ:
            case ZEND_ISSET_ISEMPTY_PROP_OBJ:
            case ZEND_FETCH_DIM_R:
            case ZEND_FETCH_OBJ_R:
            case ZEND_FETCH_DIM_IS:
            case ZEND_FETCH_OBJ_IS:
                break;
            case ZEND_ASSIGN_OP:
                return 1;
            case ZEND_ASSIGN_DIM_OP:
            case ZEND_ASSIGN_OBJ_OP:
            case ZEND_ASSIGN_STATIC_PROP_OP:
            case ZEND_ASSIGN_DIM:
            case ZEND_ASSIGN_OBJ:
            case ZEND_ASSIGN_OBJ_REF:
                break;
            case ZEND_PRE_INC_OBJ:
            case ZEND_PRE_DEC_OBJ:
            case ZEND_POST_INC_OBJ:
            case ZEND_POST_DEC_OBJ:
                break;
            case ZEND_INIT_ARRAY:
            case ZEND_ADD_ARRAY_ELEMENT:
                if (opline->extended_value & ZEND_ARRAY_ELEMENT_REF) {
                    return 1;
                }
                if (OP1_INFO() & MAY_BE_OBJECT) {
                    /* object aliasing */
                    return 1;
                }
                /* reference dependencies processed separately */
                break;
            case ZEND_OP_DATA:
                if ((opline-1)->opcode != ZEND_ASSIGN_DIM
                 && (opline-1)->opcode != ZEND_ASSIGN_OBJ) {
                    return 1;
                }
                if (OP1_INFO() & MAY_BE_OBJECT) {
                    /* object aliasing */
                    return 1;
                }
                opline--;
                ssa_op--;
                if (opline->op1_type != IS_CV
                 || (OP1_INFO() & MAY_BE_REF)
                 || (ssa_op->op1_def >= 0 && ssa->vars[ssa_op->op1_def].alias)) {
                    /* assignment into escaping structure */
                    return 1;
                }
                /* reference dependencies processed separately */
                break;
            default:
                return 1;
        }
    }
 
    if (ssa_op->op2_use == var) {
        switch (opline->opcode) {
            case ZEND_ASSIGN:
                if (opline->op1_type != IS_CV
                 || (OP1_INFO() & MAY_BE_REF)
                 || (ssa_op->op1_def >= 0 && ssa->vars[ssa_op->op1_def].alias)) {
                    /* assignment into escaping variable */
                    return 1;
                }
                if (opline->op2_type == IS_CV || opline->result_type != IS_UNUSED) {
                    if (OP2_INFO() & MAY_BE_OBJECT) {
                        /* object aliasing */
                        return 1;
                    }
                }
                break;
            default:
                return 1;
        }
    }
 
    if (ssa_op->result_use == var) {
        switch (opline->opcode) {
            case ZEND_ASSIGN:
            case ZEND_QM_ASSIGN:
            case ZEND_INIT_ARRAY:
            case ZEND_ADD_ARRAY_ELEMENT:
                break;
            default:
                return 1;
        }
    }
 
    return 0;
}
/* }}} */
 
zend_result zend_ssa_escape_analysis(const zend_script *script, zend_op_array *op_array, zend_ssa *ssa) /* {{{ */
{
    zend_ssa_var *ssa_vars = ssa->vars;
    int ssa_vars_count = ssa->vars_count;
    int i, root, use;
    int *ees;
    bool has_allocations;
    int num_non_escaped;
    ALLOCA_FLAG(use_heap)
 
    if (!ssa_vars) {
        return SUCCESS;
    }
 
    has_allocations = 0;
    for (i = op_array->last_var; i < ssa_vars_count; i++) {
        if (ssa_vars[i].definition >= 0
          && (ssa->var_info[i].type & (MAY_BE_ARRAY|MAY_BE_OBJECT))
          && is_allocation_def(op_array, ssa, ssa_vars[i].definition, i, script)) {
            has_allocations = 1;
            break;
        }
    }
    if (!has_allocations) {
        return SUCCESS;
    }
 
 
    /* 1. Build EES (Equi-Escape Sets) */
    ees = do_alloca(sizeof(int) * ssa_vars_count, use_heap);
    if (!ees) {
        return FAILURE;
    }
 
    if (zend_build_equi_escape_sets(ees, op_array, ssa) == FAILURE) {
        free_alloca(ees, use_heap);
        return FAILURE;
    }
 
    /* 2. Identify Allocations */
    num_non_escaped = 0;
    for (i = op_array->last_var; i < ssa_vars_count; i++) {
        root = ees[i];
        if (ssa_vars[root].escape_state > ESCAPE_STATE_NO_ESCAPE) {
            /* already escape. skip */
        } else if (ssa_vars[i].alias && (ssa->var_info[i].type & MAY_BE_REF)) {
            if (ssa_vars[root].escape_state == ESCAPE_STATE_NO_ESCAPE) {
                num_non_escaped--;
            }
            ssa_vars[root].escape_state = ESCAPE_STATE_GLOBAL_ESCAPE;
        } else if (ssa_vars[i].definition >= 0
             && (ssa->var_info[i].type & (MAY_BE_ARRAY|MAY_BE_OBJECT))) {
            if (!is_local_def(op_array, ssa, ssa_vars[i].definition, i, script)) {
                if (ssa_vars[root].escape_state == ESCAPE_STATE_NO_ESCAPE) {
                    num_non_escaped--;
                }
                ssa_vars[root].escape_state = ESCAPE_STATE_GLOBAL_ESCAPE;
            } else if (ssa_vars[root].escape_state == ESCAPE_STATE_UNKNOWN
             && is_allocation_def(op_array, ssa, ssa_vars[i].definition, i, script)) {
                ssa_vars[root].escape_state = ESCAPE_STATE_NO_ESCAPE;
                num_non_escaped++;
            }
        }
    }
 
    /* 3. Mark escaped EES */
    if (num_non_escaped) {
        for (i = 0; i < ssa_vars_count; i++) {
            if (ssa_vars[i].use_chain >= 0) {
                root = ees[i];
                if (ssa_vars[root].escape_state == ESCAPE_STATE_NO_ESCAPE) {
                    FOREACH_USE(ssa_vars + i, use) {
                        if (is_escape_use(op_array, ssa, use, i)) {
                            ssa_vars[root].escape_state = ESCAPE_STATE_GLOBAL_ESCAPE;
                            num_non_escaped--;
                            if (num_non_escaped == 0) {
                                i = ssa_vars_count;
                            }
                            break;
                        }
                    } FOREACH_USE_END();
                }
            }
        }
    }
 
    /* 4. Process referential dependencies */
    if (num_non_escaped) {
        bool changed;
 
        do {
            changed = 0;
            for (i = 0; i < ssa_vars_count; i++) {
                if (ssa_vars[i].use_chain >= 0) {
                    root = ees[i];
                    if (ssa_vars[root].escape_state == ESCAPE_STATE_NO_ESCAPE) {
                        FOREACH_USE(ssa_vars + i, use) {
                            zend_ssa_op *op = ssa->ops + use;
                            zend_op *opline = op_array->opcodes + use;
                            int enclosing_root;
 
                            if (opline->opcode == ZEND_OP_DATA &&
                                ((opline-1)->opcode == ZEND_ASSIGN_DIM ||
                                 (opline-1)->opcode == ZEND_ASSIGN_OBJ ||
                                 (opline-1)->opcode == ZEND_ASSIGN_OBJ_REF) &&
                                op->op1_use == i &&
                                (op-1)->op1_use >= 0) {
                                enclosing_root = ees[(op-1)->op1_use];
                            } else if ((opline->opcode == ZEND_INIT_ARRAY ||
                                 opline->opcode == ZEND_ADD_ARRAY_ELEMENT) &&
                                op->op1_use == i &&
                                op->result_def >= 0) {
                                enclosing_root = ees[op->result_def];
                            } else {
                                continue;
                            }
 
                            if (ssa_vars[enclosing_root].escape_state == ESCAPE_STATE_UNKNOWN ||
                                ssa_vars[enclosing_root].escape_state > ssa_vars[root].escape_state) {
                                if (ssa_vars[enclosing_root].escape_state == ESCAPE_STATE_UNKNOWN) {
                                    ssa_vars[root].escape_state = ESCAPE_STATE_GLOBAL_ESCAPE;
                                } else {
                                    ssa_vars[root].escape_state = ssa_vars[enclosing_root].escape_state;
                                }
                                if (ssa_vars[root].escape_state == ESCAPE_STATE_GLOBAL_ESCAPE) {
                                    num_non_escaped--;
                                    if (num_non_escaped == 0) {
                                        changed = 0;
                                    } else {
                                        changed = 1;
                                    }
                                    break;
                                } else {
                                    changed = 1;
                                }
                            }
                        } FOREACH_USE_END();
                    }
                }
            }
        } while (changed);
    }
 
    /* 5. Propagate values of escape sets to variables */
    for (i = 0; i < ssa_vars_count; i++) {
        root = ees[i];
        if (i != root) {
            ssa_vars[i].escape_state = ssa_vars[root].escape_state;
        }
    }
 
    free_alloca(ees, use_heap);
 
    return SUCCESS;
}
/* }}} */