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dis-bench / src /php /php-src /Zend /Optimizer /scdf.c
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/*
+----------------------------------------------------------------------+
| Zend Engine, Sparse Conditional Data Flow Propagation Framework |
+----------------------------------------------------------------------+
| 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 "Optimizer/scdf.h"
/* This defines a generic framework for sparse conditional dataflow propagation. The algorithm is
* based on "Sparse conditional constant propagation" by Wegman and Zadeck. We're using a
* generalized implementation as described in chapter 8.3 of the SSA book.
*
* Every SSA variable is associated with an element on a finite-height lattice, those value can only
* ever be lowered during the operation of the algorithm. If a value is lowered all instructions and
* phis using that value need to be reconsidered (this is done by adding the variable to a
* worklist). For phi functions the result is computed by applying the meet operation to the
* operands. This continues until a fixed point is reached.
*
* The algorithm is control-flow sensitive: All blocks except the start block are initially assumed
* to be unreachable. When considering a branch instruction, we determine the feasible successors
* based on the current state of the variable lattice. If a new edge becomes feasible we either have
* to mark the successor block executable and consider all instructions in it, or, if the target is
* already executable, we only have to reconsider the phi functions (as we only consider phi
* operands which are associated with a feasible edge).
*
* The generic framework requires the definition of three functions:
* * visit_instr() should recompute the lattice values of all SSA variables defined by an
* instruction.
* * visit_phi() should recompute the lattice value of the SSA variable defined by the phi. While
* doing this it should only consider operands for which scfg_is_edge_feasible() returns true.
* * get_feasible_successors() should determine the feasible successors for a branch instruction.
* Note that this callback only needs to handle conditional branches (with two successors).
*/
#if 0
#define DEBUG_PRINT(...) fprintf(stderr, __VA_ARGS__)
#else
#define DEBUG_PRINT(...)
#endif
void scdf_mark_edge_feasible(scdf_ctx *scdf, int from, int to) {
uint32_t edge = scdf_edge(&scdf->ssa->cfg, from, to);
if (zend_bitset_in(scdf->feasible_edges, edge)) {
/* We already handled this edge */
return;
}
DEBUG_PRINT("Marking edge %d->%d feasible\n", from, to);
zend_bitset_incl(scdf->feasible_edges, edge);
if (!zend_bitset_in(scdf->executable_blocks, to)) {
if (!zend_bitset_in(scdf->block_worklist, to)) {
DEBUG_PRINT("Adding block %d to worklist\n", to);
}
zend_bitset_incl(scdf->block_worklist, to);
} else {
/* Block is already executable, only a new edge became feasible.
* Reevaluate phi nodes to account for changed source operands. */
zend_ssa_block *ssa_block = &scdf->ssa->blocks[to];
zend_ssa_phi *phi;
for (phi = ssa_block->phis; phi; phi = phi->next) {
zend_bitset_excl(scdf->phi_var_worklist, phi->ssa_var);
scdf->handlers.visit_phi(scdf, phi);
}
}
}
void scdf_init(zend_optimizer_ctx *ctx, scdf_ctx *scdf, zend_op_array *op_array, zend_ssa *ssa) {
scdf->op_array = op_array;
scdf->ssa = ssa;
scdf->instr_worklist_len = zend_bitset_len(op_array->last);
scdf->phi_var_worklist_len = zend_bitset_len(ssa->vars_count);
scdf->block_worklist_len = zend_bitset_len(ssa->cfg.blocks_count);
scdf->instr_worklist = zend_arena_calloc(&ctx->arena,
scdf->instr_worklist_len + scdf->phi_var_worklist_len + 2 * scdf->block_worklist_len + zend_bitset_len(ssa->cfg.edges_count),
sizeof(zend_ulong));
scdf->phi_var_worklist = scdf->instr_worklist + scdf->instr_worklist_len;
scdf->block_worklist = scdf->phi_var_worklist + scdf->phi_var_worklist_len;
scdf->executable_blocks = scdf->block_worklist + scdf->block_worklist_len;
scdf->feasible_edges = scdf->executable_blocks + scdf->block_worklist_len;
zend_bitset_incl(scdf->block_worklist, 0);
zend_bitset_incl(scdf->executable_blocks, 0);
}
void scdf_solve(scdf_ctx *scdf, const char *name) {
zend_ssa *ssa = scdf->ssa;
DEBUG_PRINT("Start SCDF solve (%s)\n", name);
while (!zend_bitset_empty(scdf->instr_worklist, scdf->instr_worklist_len)
|| !zend_bitset_empty(scdf->phi_var_worklist, scdf->phi_var_worklist_len)
|| !zend_bitset_empty(scdf->block_worklist, scdf->block_worklist_len)
) {
int i;
while ((i = zend_bitset_pop_first(scdf->phi_var_worklist, scdf->phi_var_worklist_len)) >= 0) {
zend_ssa_phi *phi = ssa->vars[i].definition_phi;
ZEND_ASSERT(phi);
if (zend_bitset_in(scdf->executable_blocks, phi->block)) {
scdf->handlers.visit_phi(scdf, phi);
}
}
while ((i = zend_bitset_pop_first(scdf->instr_worklist, scdf->instr_worklist_len)) >= 0) {
int block_num = ssa->cfg.map[i];
if (zend_bitset_in(scdf->executable_blocks, block_num)) {
zend_basic_block *block = &ssa->cfg.blocks[block_num];
zend_op *opline = &scdf->op_array->opcodes[i];
zend_ssa_op *ssa_op = &ssa->ops[i];
if (opline->opcode == ZEND_OP_DATA) {
opline--;
ssa_op--;
}
scdf->handlers.visit_instr(scdf, opline, ssa_op);
if (i == block->start + block->len - 1) {
if (block->successors_count == 1) {
scdf_mark_edge_feasible(scdf, block_num, block->successors[0]);
} else if (block->successors_count > 1) {
scdf->handlers.mark_feasible_successors(scdf, block_num, block, opline, ssa_op);
}
}
}
}
while ((i = zend_bitset_pop_first(scdf->block_worklist, scdf->block_worklist_len)) >= 0) {
/* This block is now live. Interpret phis and instructions in it. */
zend_basic_block *block = &ssa->cfg.blocks[i];
zend_ssa_block *ssa_block = &ssa->blocks[i];
DEBUG_PRINT("Pop block %d from worklist\n", i);
zend_bitset_incl(scdf->executable_blocks, i);
{
zend_ssa_phi *phi;
for (phi = ssa_block->phis; phi; phi = phi->next) {
zend_bitset_excl(scdf->phi_var_worklist, phi->ssa_var);
scdf->handlers.visit_phi(scdf, phi);
}
}
if (block->len == 0) {
/* Zero length blocks don't have a last instruction that would normally do this */
scdf_mark_edge_feasible(scdf, i, block->successors[0]);
} else {
zend_op *opline = NULL;
int j, end = block->start + block->len;
for (j = block->start; j < end; j++) {
opline = &scdf->op_array->opcodes[j];
zend_bitset_excl(scdf->instr_worklist, j);
if (opline->opcode != ZEND_OP_DATA) {
scdf->handlers.visit_instr(scdf, opline, &ssa->ops[j]);
}
}
if (block->successors_count == 1) {
scdf_mark_edge_feasible(scdf, i, block->successors[0]);
} else if (block->successors_count > 1) {
ZEND_ASSERT(opline && "Should have opline in non-empty block");
if (opline->opcode == ZEND_OP_DATA) {
opline--;
j--;
}
scdf->handlers.mark_feasible_successors(scdf, i, block, opline, &ssa->ops[j-1]);
}
}
}
}
}
/* If a live range starts in a reachable block and ends in an unreachable block, we should
* not eliminate the latter. While it cannot be reached, the FREE opcode of the loop var
* is necessary for the correctness of temporary compaction. */
static bool is_live_loop_var_free(
scdf_ctx *scdf, const zend_op *opline, const zend_ssa_op *ssa_op) {
if (!zend_optimizer_is_loop_var_free(opline)) {
return false;
}
int var = ssa_op->op1_use;
if (var < 0) {
return false;
}
zend_ssa_var *ssa_var = &scdf->ssa->vars[var];
uint32_t def_block;
if (ssa_var->definition >= 0) {
def_block = scdf->ssa->cfg.map[ssa_var->definition];
} else {
def_block = ssa_var->definition_phi->block;
}
return zend_bitset_in(scdf->executable_blocks, def_block);
}
static bool kept_alive_by_loop_var_free(scdf_ctx *scdf, const zend_basic_block *block) {
const zend_op_array *op_array = scdf->op_array;
const zend_cfg *cfg = &scdf->ssa->cfg;
if (!(cfg->flags & ZEND_FUNC_FREE_LOOP_VAR)) {
return false;
}
for (uint32_t i = block->start; i < block->start + block->len; i++) {
if (is_live_loop_var_free(scdf, &op_array->opcodes[i], &scdf->ssa->ops[i])) {
return true;
}
}
return false;
}
static uint32_t cleanup_loop_var_free_block(scdf_ctx *scdf, zend_basic_block *block) {
zend_ssa *ssa = scdf->ssa;
const zend_op_array *op_array = scdf->op_array;
const zend_cfg *cfg = &ssa->cfg;
int block_num = block - cfg->blocks;
uint32_t removed_ops = 0;
/* Removes phi nodes */
for (zend_ssa_phi *phi = ssa->blocks[block_num].phis; phi; phi = phi->next) {
zend_ssa_remove_uses_of_var(ssa, phi->ssa_var);
zend_ssa_remove_phi(ssa, phi);
}
for (uint32_t i = block->start; i < block->start + block->len; i++) {
zend_op *opline = &op_array->opcodes[i];
zend_ssa_op *ssa_op = &scdf->ssa->ops[i];
if (opline->opcode == ZEND_NOP
|| is_live_loop_var_free(scdf, opline, ssa_op)) {
continue;
}
/* While we have to preserve the loop var free, we can still remove other instructions
* in the block. */
zend_ssa_remove_defs_of_instr(ssa, ssa_op);
zend_ssa_remove_instr(ssa, opline, ssa_op);
removed_ops++;
}
zend_ssa_remove_block_from_cfg(ssa, block_num);
return removed_ops;
}
/* Removes unreachable blocks. This will remove both the instructions (and phis) in the
* blocks, as well as remove them from the successor / predecessor lists and mark them
* unreachable. Blocks already marked unreachable are not removed. */
uint32_t scdf_remove_unreachable_blocks(scdf_ctx *scdf) {
zend_ssa *ssa = scdf->ssa;
int i;
uint32_t removed_ops = 0;
for (i = 0; i < ssa->cfg.blocks_count; i++) {
zend_basic_block *block = &ssa->cfg.blocks[i];
if (!zend_bitset_in(scdf->executable_blocks, i) && (block->flags & ZEND_BB_REACHABLE)) {
if (!kept_alive_by_loop_var_free(scdf, block)) {
removed_ops += block->len;
zend_ssa_remove_block(scdf->op_array, ssa, i);
} else {
removed_ops += cleanup_loop_var_free_block(scdf, block);
}
}
}
return removed_ops;
}