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