mono/mini/linear-scan.c

   1 /*
   2  * liveness.c: liveness analysis
   3  *
   4  * Author:
   5  *   Dietmar Maurer (dietmar@ximian.com)
   6  *
   7  * (C) 2002 Ximian, Inc.
   8  */
   9
  10 #include "mini.h"
  11 #include <mono/metadata/debug-helpers.h>
  12
  13 #ifndef DISABLE_JIT
  14
  15 static void mono_linear_scan2 (MonoCompile *cfg, GList *vars, GList *regs, regmask_t *used_mask);
  16
  17 GList *
  18 mono_varlist_insert_sorted (MonoCompile *cfg, GList *list, MonoMethodVar *mv, int sort_type)
  19 {
  20         GList *l;
  21
  22         if (!list)
  23                 return g_list_prepend (NULL, mv);
  24
  25         for (l = list; l; l = l->next) {
  26                 MonoMethodVar *v1 = l->data;
  27
  28                 if (sort_type == 2) {
  29                         if (mv->spill_costs >= v1->spill_costs) {
  30                                 list = g_list_insert_before (list, l, mv);
  31                                 break;
  32                         }
  33                 } else if (sort_type == 1) {
  34                         if (mv->range.last_use.abs_pos <= v1->range.last_use.abs_pos) {
  35                                 list = g_list_insert_before (list, l, mv);
  36                                 break;
  37                         }
  38                 } else {
  39                         if (mv->range.first_use.abs_pos <= v1->range.first_use.abs_pos) {
  40                                 list = g_list_insert_before (list, l, mv);
  41                                 break;
  42                         }
  43                 }
  44         }
  45         if (!l)
  46                 list = g_list_append (list, mv);
  47
  48         return list;
  49 }
  50
  51 static gint
  52 compare_by_first_use_func (gconstpointer a, gconstpointer b)
  53 {
  54         MonoMethodVar *v1 = (MonoMethodVar*)a;
  55         MonoMethodVar *v2 = (MonoMethodVar*)b;
  56
  57         return v1->range.first_use.abs_pos - v2->range.first_use.abs_pos;
  58 }
  59
  60 GList *
  61 mono_varlist_sort (MonoCompile *cfg, GList *list, int sort_type)
  62 {
  63         if (sort_type == 0)
  64                 return g_list_sort (list, compare_by_first_use_func);
  65         else
  66                 g_assert_not_reached ();
  67
  68         return NULL;
  69 }
  70
  71 // #define DEBUG_LSCAN
  72
  73 void
  74 mono_linear_scan (MonoCompile *cfg, GList *vars, GList *regs, regmask_t *used_mask)
  75 {
  76         GList *l, *a, *active = NULL;
  77         MonoMethodVar *vmv, *amv;
  78         int max_regs, n_regvars;
  79         int gains [sizeof (regmask_t) * 8];
  80         regmask_t used_regs = 0;
  81         gboolean cost_driven;
  82
  83         if (vars && (((MonoMethodVar*)vars->data)->interval != NULL)) {
  84                 mono_linear_scan2 (cfg, vars, regs, used_mask);
  85                 return;
  86         }
  87
  88         cost_driven = TRUE;
  89
  90 #ifdef DEBUG_LSCAN
  91         printf ("Linears scan for %s\n", mono_method_full_name (cfg->method, TRUE));
  92 #endif
  93
  94 #ifdef DEBUG_LSCAN
  95         for (l = vars; l; l = l->next) {
  96                 vmv = l->data;
  97                 printf ("VAR %d %08x %08x C%d\n", vmv->idx, vmv->range.first_use.abs_pos,
  98                         vmv->range.last_use.abs_pos, vmv->spill_costs);
  99         }
 100 #endif
 101         max_regs = g_list_length (regs);
 102
 103         for (l = regs; l; l = l->next) {
 104                 int regnum = GPOINTER_TO_INT (l->data);
 105                 g_assert (regnum < G_N_ELEMENTS (gains));
 106                 gains [regnum] = 0;
 107         }
 108
 109         /* linear scan */
 110         for (l = vars; l; l = l->next) {
 111                 vmv = l->data;
 112
 113 #ifdef DEBUG_LSCAN
 114                 printf ("START  %2d %08x %08x\n",  vmv->idx, vmv->range.first_use.abs_pos,
 115                         vmv->range.last_use.abs_pos);
 116 #endif
 117                 /* expire old intervals in active */
 118                 if (!cfg->disable_reuse_registers) {
 119                         while (active) {
 120                                 amv = (MonoMethodVar *)active->data;
 121
 122                                 if (amv->range.last_use.abs_pos > vmv->range.first_use.abs_pos)
 123                                         break;
 124
 125 #ifdef DEBUG_LSCAN
 126                                 printf ("EXPIR  %2d %08x %08x C%d R%d\n", amv->idx, amv->range.first_use.abs_pos,
 127                                                 amv->range.last_use.abs_pos, amv->spill_costs, amv->reg);
 128 #endif
 129                                 active = g_list_delete_link (active, active);
 130                                 regs = g_list_prepend (regs, GINT_TO_POINTER (amv->reg));
 131                                 gains [amv->reg] += amv->spill_costs;
 132                         }
 133                 }
 134
 135                 if (active && g_list_length (active) == max_regs) {
 136                         /* Spill */
 137
 138                         a = g_list_nth (active, max_regs - 1);
 139                         amv = (MonoMethodVar *)a->data;
 140
 141                         if ((cost_driven && amv->spill_costs < vmv->spill_costs) ||
 142                             (!cost_driven && amv->range.last_use.abs_pos > vmv->range.last_use.abs_pos)) {
 143                                 vmv->reg = amv->reg;
 144                                 amv->reg = -1;
 145                                 active = g_list_delete_link (active, a);
 146
 147                                 if (cost_driven)
 148                                         active = mono_varlist_insert_sorted (cfg, active, vmv, 2);
 149                                 else
 150                                         active = mono_varlist_insert_sorted (cfg, active, vmv, 1);
 151
 152 #ifdef DEBUG_LSCAN
 153                                 printf ("SPILL0 %2d %08x %08x C%d\n",  amv->idx,
 154                                         amv->range.first_use.abs_pos, amv->range.last_use.abs_pos,
 155                                         amv->spill_costs);
 156 #endif
 157                         } else {
 158 #ifdef DEBUG_LSCAN
 159                                 printf ("SPILL1 %2d %08x %08x C%d\n",  vmv->idx,
 160                                         vmv->range.first_use.abs_pos, vmv->range.last_use.abs_pos,
 161                                         vmv->spill_costs);
 162 #endif
 163                                 vmv->reg = -1;
 164                         }
 165                 } else {
 166                         /* assign register */
 167
 168                         g_assert (regs);
 169
 170                         vmv->reg = GPOINTER_TO_INT (regs->data);
 171
 172                         used_regs |= 1LL << vmv->reg;
 173
 174                         regs = g_list_delete_link (regs, regs);
 175
 176 #ifdef DEBUG_LSCAN
 177                         printf ("ADD    %2d %08x %08x C%d R%d\n",  vmv->idx,
 178                                 vmv->range.first_use.abs_pos, vmv->range.last_use.abs_pos,
 179                                 vmv->spill_costs, vmv->reg);
 180 #endif
 181                         active = mono_varlist_insert_sorted (cfg, active, vmv, TRUE);
 182                 }
 183
 184
 185 #ifdef DEBUG_LSCAN
 186                 for (a = active; a; a = a->next) {
 187                         amv = (MonoMethodVar *)a->data;
 188                         printf ("ACT    %2d %08x %08x C%d R%d\n", amv->idx, amv->range.first_use.abs_pos,
 189                                 amv->range.last_use.abs_pos, amv->spill_costs, amv->reg);
 190                 }
 191                 printf ("NEXT\n");
 192 #endif
 193         }
 194
 195         for (a = active; a; a = a->next) {
 196                 amv = (MonoMethodVar *)a->data;
 197                 gains [amv->reg] += amv->spill_costs;
 198         }
 199
 200         n_regvars = 0;
 201         for (l = vars; l; l = l->next) {
 202                 vmv = l->data;
 203
 204                 if (vmv->reg >= 0)  {
 205                         if ((gains [vmv->reg] > mono_arch_regalloc_cost (cfg, vmv)) && (cfg->varinfo [vmv->idx]->opcode != OP_REGVAR)) {
 206                                 if (cfg->verbose_level > 2) {
 207                                         printf ("ALLOCATED R%d(%d) TO HREG %d COST %d\n", cfg->varinfo [vmv->idx]->dreg, vmv->idx, vmv->reg, vmv->spill_costs);
 208                                 }
 209                                 cfg->varinfo [vmv->idx]->opcode = OP_REGVAR;
 210                                 cfg->varinfo [vmv->idx]->dreg = vmv->reg;
 211                                 n_regvars ++;
 212                         } else {
 213                                 if (cfg->verbose_level > 2)
 214                                         printf ("COSTLY: R%d C%d C%d %s\n", vmv->idx, vmv->spill_costs, mono_arch_regalloc_cost (cfg, vmv), mono_arch_regname (vmv->reg));
 215                                 vmv->reg = -1;
 216                         }
 217                 }
 218
 219                 if (vmv->reg == -1) {
 220                         if (cfg->verbose_level > 2)
 221                                 printf ("NOT REGVAR: %d\n", vmv->idx);
 222                 }
 223         }
 224
 225         cfg->stat_n_regvars = n_regvars;
 226
 227         /* Compute used regs */
 228         used_regs = 0;
 229         for (l = vars; l; l = l->next) {
 230                 vmv = l->data;
 231
 232                 if (vmv->reg >= 0)
 233                         used_regs |= 1LL << vmv->reg;
 234         }
 235
 236         *used_mask |= used_regs;
 237
 238 #ifdef DEBUG_LSCAN
 239         if (cfg->verbose_level > 2)
 240                 printf ("EXIT: final used mask: %08x\n", *used_mask);
 241 #endif
 242
 243         g_list_free (regs);
 244         g_list_free (active);
 245         g_list_free (vars);
 246 }
 247
 248 static gint
 249 compare_by_interval_start_pos_func (gconstpointer a, gconstpointer b)
 250 {
 251         MonoMethodVar *v1 = (MonoMethodVar*)a;
 252         MonoMethodVar *v2 = (MonoMethodVar*)b;
 253
 254         if (v1 == v2)
 255                 return 0;
 256         else if (v1->interval->range && v2->interval->range)
 257                 return v1->interval->range->from - v2->interval->range->from;
 258         else if (v1->interval->range)
 259                 return -1;
 260         else
 261                 return 1;
 262 }
 263
 264 #if 0
 265 #define LSCAN_DEBUG(a) do { a; } while (0)
 266 #else
 267 #define LSCAN_DEBUG(a)
 268 #endif
 269
 270 /* FIXME: This is x86 only */
 271 static inline guint32
 272 regalloc_cost (MonoCompile *cfg, MonoMethodVar *vmv)
 273 {
 274         MonoInst *ins = cfg->varinfo [vmv->idx];
 275
 276         /* Load if it is an argument */
 277         return (ins->opcode == OP_ARG) ? 1 : 0;
 278 }
 279
 280 void
 281 mono_linear_scan2 (MonoCompile *cfg, GList *vars, GList *regs, regmask_t *used_mask)
 282 {
 283         GList *unhandled, *active, *inactive, *l;
 284         MonoMethodVar *vmv;
 285         gint32 free_pos [sizeof (regmask_t) * 8];
 286         gint32 gains [sizeof (regmask_t) * 8];
 287         regmask_t used_regs = 0;
 288         int n_regs, n_regvars, i;
 289
 290         for (l = vars; l; l = l->next) {
 291                 vmv = l->data;
 292                 LSCAN_DEBUG (printf ("VAR R%d %08x %08x C%d\n", cfg->varinfo [vmv->idx]->dreg, vmv->range.first_use.abs_pos,
 293                                                          vmv->range.last_use.abs_pos, vmv->spill_costs));
 294         }
 295
 296         LSCAN_DEBUG (printf ("Linear Scan 2 for %s:\n", mono_method_full_name (cfg->method, TRUE)));
 297
 298         n_regs = g_list_length (regs);
 299         memset (gains, 0, n_regs * sizeof (gint32));
 300         unhandled = g_list_sort (g_list_copy (vars), compare_by_interval_start_pos_func);
 301         active = NULL;
 302         inactive = NULL;
 303
 304         while (unhandled) {
 305                 MonoMethodVar *current = unhandled->data;
 306                 int pos, reg, max_free_pos;
 307                 gboolean changed;
 308
 309                 unhandled = g_list_delete_link (unhandled, unhandled);
 310
 311                 LSCAN_DEBUG (printf ("Processing R%d: ", cfg->varinfo [current->idx]->dreg));
 312                 LSCAN_DEBUG (mono_linterval_print (current->interval));
 313                 LSCAN_DEBUG (printf ("\n"));
 314
 315                 if (!current->interval->range)
 316                         continue;
 317
 318                 pos = current->interval->range->from;
 319
 320                 /* Check for intervals in active which expired or inactive */
 321                 changed = TRUE;
 322                 /* FIXME: Optimize this */
 323                 while (changed) {
 324                         changed = FALSE;
 325                         for (l = active; l != NULL; l = l->next) {
 326                                 MonoMethodVar *v = (MonoMethodVar*)l->data;
 327
 328                                 if (v->interval->last_range->to < pos) {
 329                                         active = g_list_delete_link (active, l);
 330                                         LSCAN_DEBUG (printf ("Interval R%d has expired\n", cfg->varinfo [v->idx]->dreg));
 331                                         changed = TRUE;
 332                                         break;
 333                                 }
 334                                 else if (!mono_linterval_covers (v->interval, pos)) {
 335                                         inactive = g_list_append (inactive, v);
 336                                         active = g_list_delete_link (active, l);
 337                                         LSCAN_DEBUG (printf ("Interval R%d became inactive\n", cfg->varinfo [v->idx]->dreg));
 338                                         changed = TRUE;
 339                                         break;
 340                                 }
 341                         }
 342                 }
 343
 344                 /* Check for intervals in inactive which expired or active */
 345                 changed = TRUE;
 346                 /* FIXME: Optimize this */
 347                 while (changed) {
 348                         changed = FALSE;
 349                         for (l = inactive; l != NULL; l = l->next) {
 350                                 MonoMethodVar *v = (MonoMethodVar*)l->data;
 351
 352                                 if (v->interval->last_range->to < pos) {
 353                                         inactive = g_list_delete_link (inactive, l);
 354                                         LSCAN_DEBUG (printf ("\tInterval R%d has expired\n", cfg->varinfo [v->idx]->dreg));
 355                                         changed = TRUE;
 356                                         break;
 357                                 }
 358                                 else if (mono_linterval_covers (v->interval, pos)) {
 359                                         active = g_list_append (active, v);
 360                                         inactive = g_list_delete_link (inactive, l);
 361                                         LSCAN_DEBUG (printf ("\tInterval R%d became active\n", cfg->varinfo [v->idx]->dreg));
 362                                         changed = TRUE;
 363                                         break;
 364                                 }
 365                         }
 366                 }
 367
 368                 /* Find a register for the current interval */
 369                 for (i = 0; i < n_regs; ++i)
 370                         free_pos [i] = ((gint32)0x7fffffff);
 371
 372                 for (l = active; l != NULL; l = l->next) {
 373                         MonoMethodVar *v = (MonoMethodVar*)l->data;
 374
 375                         if (v->reg >= 0) {
 376                                 free_pos [v->reg] = 0;
 377                                 LSCAN_DEBUG (printf ("\threg %d is busy (cost %d)\n", v->reg, v->spill_costs));
 378                         }
 379                 }
 380
 381                 for (l = inactive; l != NULL; l = l->next) {
 382                         MonoMethodVar *v = (MonoMethodVar*)l->data;
 383                         gint32 intersect_pos;
 384
 385                         if (v->reg >= 0) {
 386                                 intersect_pos = mono_linterval_get_intersect_pos (current->interval, v->interval);
 387                                 if (intersect_pos != -1) {
 388                                         free_pos [v->reg] = intersect_pos;
 389                                         LSCAN_DEBUG (printf ("\threg %d becomes free at %d\n", v->reg, intersect_pos));
 390                                 }
 391                         }
 392                 }
 393
 394                 max_free_pos = -1;
 395                 reg = -1;
 396                 for (i = 0; i < n_regs; ++i)
 397                         if (free_pos [i] > max_free_pos) {
 398                                 reg = i;
 399                                 max_free_pos = free_pos [i];
 400                         }
 401
 402                 g_assert (reg != -1);
 403
 404                 if (free_pos [reg] >= current->interval->last_range->to) {
 405                         /* Register available for whole interval */
 406                         current->reg = reg;
 407                         LSCAN_DEBUG (printf ("\tAssigned hreg %d to R%d\n", reg, cfg->varinfo [current->idx]->dreg));
 408
 409                         active = g_list_append (active, current);
 410                         gains [current->reg] += current->spill_costs;
 411                 }
 412                 else {
 413                         /*
 414                          * free_pos [reg] > 0 means there is a register available for parts
 415                          * of the interval, so splitting it is possible. This is not yet
 416                          * supported, so we spill in this case too.
 417                          */
 418
 419                         /* Spill an interval */
 420
 421                         /* FIXME: Optimize the selection of the interval */
 422
 423                         if (active) {
 424                                 GList *min_spill_pos;
 425 #if 0
 426                                 /*
 427                                  * This favors registers with big spill costs, thus larger liveness ranges,
 428                                  * thus actually leading to worse code size.
 429                                  */
 430                                 guint32 min_spill_value = G_MAXINT32;
 431
 432                                 for (l = active; l != NULL; l = l->next) {
 433                                         vmv = (MonoMethodVar*)l->data;
 434
 435                                         if (vmv->spill_costs < min_spill_value) {
 436                                                 min_spill_pos = l;
 437                                                 min_spill_value = vmv->spill_costs;
 438                                         }
 439                                 }
 440 #else
 441                                 /* Spill either the first active or the current interval */
 442                                 min_spill_pos = active;
 443 #endif
 444                                 vmv = (MonoMethodVar*)min_spill_pos->data;
 445                                 if (vmv->spill_costs < current->spill_costs) {
 446                                 //                              if (vmv->interval->last_range->to < current->interval->last_range->to) {
 447                                         gains [vmv->reg] -= vmv->spill_costs;
 448                                         vmv->reg = -1;
 449                                         LSCAN_DEBUG (printf ("\tSpilled R%d\n", cfg->varinfo [vmv->idx]->dreg));
 450                                         active = g_list_delete_link (active, min_spill_pos);
 451                                 }
 452                                 else
 453                                         LSCAN_DEBUG (printf ("\tSpilled current (cost %d)\n", current->spill_costs));
 454                         }
 455                         else
 456                                 LSCAN_DEBUG (printf ("\tSpilled current\n"));
 457                 }
 458         }
 459
 460         /* Decrease the gains by the cost of saving+restoring the register */
 461         for (i = 0; i < n_regs; ++i) {
 462                 if (gains [i]) {
 463                         /* FIXME: This is x86 only */
 464                         gains [i] -= cfg->method->save_lmf ? 1 : 2;
 465                         if (gains [i] < 0)
 466                                 gains [i] = 0;
 467                 }
 468         }
 469
 470         /* Do the actual register assignment */
 471         n_regvars = 0;
 472         for (l = vars; l; l = l->next) {
 473                 vmv = l->data;
 474
 475                 if (vmv->reg >= 0) {
 476                         int reg_index = vmv->reg;
 477
 478                         /* During allocation, vmv->reg is an index into the regs list */
 479                         vmv->reg = GPOINTER_TO_INT (g_list_nth_data (regs, vmv->reg));
 480
 481                         if ((gains [reg_index] > regalloc_cost (cfg, vmv)) && (cfg->varinfo [vmv->idx]->opcode != OP_REGVAR)) {
 482                                 if (cfg->verbose_level > 2)
 483                                         printf ("REGVAR R%d G%d C%d %s\n", cfg->varinfo [vmv->idx]->dreg, gains [reg_index], regalloc_cost (cfg, vmv), mono_arch_regname (vmv->reg));
 484                                 cfg->varinfo [vmv->idx]->opcode = OP_REGVAR;
 485                                 cfg->varinfo [vmv->idx]->dreg = vmv->reg;
 486                                 n_regvars ++;
 487                         }
 488                         else {
 489                                 if (cfg->verbose_level > 2)
 490                                         printf ("COSTLY: %s R%d G%d C%d %s\n", mono_method_full_name (cfg->method, TRUE), cfg->varinfo [vmv->idx]->dreg, gains [reg_index], regalloc_cost (cfg, vmv), mono_arch_regname (vmv->reg));
 491                                 vmv->reg = -1;
 492                         }
 493                 }
 494         }
 495
 496         cfg->stat_n_regvars = n_regvars;
 497
 498         /* Compute used regs */
 499         used_regs = 0;
 500         for (l = vars; l; l = l->next) {
 501                 vmv = l->data;
 502
 503                 if (vmv->reg >= 0)
 504                         used_regs |= 1LL << vmv->reg;
 505         }
 506
 507         *used_mask |= used_regs;
 508
 509         g_list_free (active);
 510         g_list_free (inactive);
 511 }
 512
 513 #endif /* #ifndef DISABLE_JIT */