memops.c

   1 /*
   2  * memops - try to combine memory ops.
   3  *
   4  * Copyright (C) 2004 Linus Torvalds
   5  */
   6
   7 #include <string.h>
   8 #include <stdarg.h>
   9 #include <stdlib.h>
  10 #include <stdio.h>
  11 #include <stddef.h>
  12 #include <assert.h>
  13
  14 #include "parse.h"
  15 #include "expression.h"
  16 #include "linearize.h"
  17 #include "simplify.h"
  18 #include "flow.h"
  19
  20 /*
  21  * We should probably sort the phi list just to make it easier to compare
  22  * later for equality.
  23  */
  24 static void rewrite_load_instruction(struct instruction *insn, struct pseudo_list *dominators)
  25 {
  26         pseudo_t new, phi;
  27
  28         /*
  29          * Check for somewhat common case of duplicate
  30          * phi nodes.
  31          */
  32         new = first_pseudo(dominators)->def->phi_src;
  33         FOR_EACH_PTR(dominators, phi) {
  34                 if (new != phi->def->phi_src)
  35                         goto complex_phi;
  36                 new->ident = new->ident ? : phi->ident;
  37         } END_FOR_EACH_PTR(phi);
  38
  39         /*
  40          * All the same pseudo - mark the phi-nodes unused
  41          * and convert the load into a LNOP and replace the
  42          * pseudo.
  43          */
  44         replace_with_pseudo(insn, new);
  45         FOR_EACH_PTR(dominators, phi) {
  46                 kill_instruction(phi->def);
  47         } END_FOR_EACH_PTR(phi);
  48         goto end;
  49
  50 complex_phi:
  51         /* We leave symbol pseudos with a bogus usage list here */
  52         if (insn->src->type != PSEUDO_SYM)
  53                 kill_use(&insn->src);
  54         insn->opcode = OP_PHI;
  55         insn->phi_list = dominators;
  56
  57 end:
  58         repeat_phase |= REPEAT_CSE;
  59 }
  60
  61 static int find_dominating_parents(pseudo_t pseudo, struct instruction *insn,
  62         struct basic_block *bb, unsigned long generation, struct pseudo_list **dominators,
  63         int local)
  64 {
  65         struct basic_block *parent;
  66
  67         FOR_EACH_PTR(bb->parents, parent) {
  68                 struct instruction *one;
  69                 struct instruction *br;
  70                 pseudo_t phi;
  71
  72                 FOR_EACH_PTR_REVERSE(parent->insns, one) {
  73                         int dominance;
  74                         if (!one->bb)
  75                                 continue;
  76                         if (one == insn)
  77                                 goto no_dominance;
  78                         dominance = dominates(pseudo, insn, one, local);
  79                         if (dominance < 0) {
  80                                 if (one->opcode == OP_LOAD)
  81                                         continue;
  82                                 return 0;
  83                         }
  84                         if (!dominance)
  85                                 continue;
  86                         goto found_dominator;
  87                 } END_FOR_EACH_PTR_REVERSE(one);
  88 no_dominance:
  89                 if (parent->generation == generation)
  90                         continue;
  91                 parent->generation = generation;
  92
  93                 if (!find_dominating_parents(pseudo, insn, parent, generation, dominators, local))
  94                         return 0;
  95                 continue;
  96
  97 found_dominator:
  98                 br = delete_last_instruction(&parent->insns);
  99                 phi = alloc_phi(parent, one->target, one->type);
 100                 phi->ident = phi->ident ? : one->target->ident;
 101                 add_instruction(&parent->insns, br);
 102                 use_pseudo(insn, phi, add_pseudo(dominators, phi));
 103         } END_FOR_EACH_PTR(parent);
 104         return 1;
 105 }
 106
 107 static int address_taken(pseudo_t pseudo)
 108 {
 109         struct pseudo_user *pu;
 110         FOR_EACH_PTR(pseudo->users, pu) {
 111                 struct instruction *insn = pu->insn;
 112                 if (insn->bb && (insn->opcode != OP_LOAD && insn->opcode != OP_STORE))
 113                         return 1;
 114                 if (pu->userp != &insn->src)
 115                         return 1;
 116         } END_FOR_EACH_PTR(pu);
 117         return 0;
 118 }
 119
 120 static int local_pseudo(pseudo_t pseudo)
 121 {
 122         return pseudo->type == PSEUDO_SYM
 123                 && !(pseudo->sym->ctype.modifiers & (MOD_STATIC | MOD_NONLOCAL))
 124                 && !address_taken(pseudo);
 125 }
 126
 127 static bool compatible_loads(struct instruction *a, struct instruction *b)
 128 {
 129         if (is_integral_type(a->type) && is_float_type(b->type))
 130                 return false;
 131         if (is_float_type(a->type) && is_integral_type(b->type))
 132                 return false;
 133         return true;
 134 }
 135
 136 static void simplify_loads(struct basic_block *bb)
 137 {
 138         struct instruction *insn;
 139
 140         FOR_EACH_PTR_REVERSE(bb->insns, insn) {
 141                 if (!insn->bb)
 142                         continue;
 143                 if (insn->opcode == OP_LOAD) {
 144                         struct instruction *dom;
 145                         pseudo_t pseudo = insn->src;
 146                         int local = local_pseudo(pseudo);
 147                         struct pseudo_list *dominators;
 148                         unsigned long generation;
 149
 150                         if (insn->is_volatile)
 151                                 continue;
 152
 153                         if (!has_users(insn->target)) {
 154                                 kill_instruction(insn);
 155                                 continue;
 156                         }
 157
 158                         RECURSE_PTR_REVERSE(insn, dom) {
 159                                 int dominance;
 160                                 if (!dom->bb)
 161                                         continue;
 162                                 dominance = dominates(pseudo, insn, dom, local);
 163                                 if (dominance) {
 164                                         /* possible partial dominance? */
 165                                         if (dominance < 0)  {
 166                                                 if (dom->opcode == OP_LOAD)
 167                                                         continue;
 168                                                 goto next_load;
 169                                         }
 170                                         if (!compatible_loads(insn, dom))
 171                                                 goto next_load;
 172                                         /* Yeehaa! Found one! */
 173                                         replace_with_pseudo(insn, dom->target);
 174                                         goto next_load;
 175                                 }
 176                         } END_FOR_EACH_PTR_REVERSE(dom);
 177
 178                         /* OK, go find the parents */
 179                         generation = ++bb_generation;
 180                         bb->generation = generation;
 181                         dominators = NULL;
 182                         if (find_dominating_parents(pseudo, insn, bb, generation, &dominators, local)) {
 183                                 /* This happens with initial assignments to structures etc.. */
 184                                 if (!dominators) {
 185                                         if (local) {
 186                                                 assert(pseudo->type != PSEUDO_ARG);
 187                                                 replace_with_pseudo(insn, value_pseudo(0));
 188                                         }
 189                                         goto next_load;
 190                                 }
 191                                 rewrite_load_instruction(insn, dominators);
 192                         } else {        // cleanup pending phi-sources
 193                                 int repeat = repeat_phase;
 194                                 pseudo_t phi;
 195                                 FOR_EACH_PTR(dominators, phi) {
 196                                         kill_instruction(phi->def);
 197                                 } END_FOR_EACH_PTR(phi);
 198                                 repeat_phase = repeat;
 199                         }
 200                 }
 201 next_load:
 202                 /* Do the next one */;
 203         } END_FOR_EACH_PTR_REVERSE(insn);
 204 }
 205
 206 static void kill_dominated_stores(struct basic_block *bb)
 207 {
 208         struct instruction *insn;
 209
 210         FOR_EACH_PTR_REVERSE(bb->insns, insn) {
 211                 if (!insn->bb)
 212                         continue;
 213                 if (insn->opcode == OP_STORE) {
 214                         struct instruction *dom;
 215                         pseudo_t pseudo = insn->src;
 216                         int local;
 217
 218                         if (!insn->type)
 219                                 continue;
 220                         if (insn->is_volatile)
 221                                 continue;
 222
 223                         local = local_pseudo(pseudo);
 224                         RECURSE_PTR_REVERSE(insn, dom) {
 225                                 int dominance;
 226                                 if (!dom->bb)
 227                                         continue;
 228                                 dominance = dominates(pseudo, insn, dom, local);
 229                                 if (dominance) {
 230                                         /* possible partial dominance? */
 231                                         if (dominance < 0)
 232                                                 goto next_store;
 233                                         if (dom->opcode == OP_LOAD)
 234                                                 goto next_store;
 235                                         /* Yeehaa! Found one! */
 236                                         kill_instruction_force(dom);
 237                                 }
 238                         } END_FOR_EACH_PTR_REVERSE(dom);
 239
 240                         /* OK, we should check the parents now */
 241                 }
 242 next_store:
 243                 /* Do the next one */;
 244         } END_FOR_EACH_PTR_REVERSE(insn);
 245 }
 246
 247 void simplify_memops(struct entrypoint *ep)
 248 {
 249         struct basic_block *bb;
 250         pseudo_t pseudo;
 251
 252         FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
 253                 simplify_loads(bb);
 254         } END_FOR_EACH_PTR_REVERSE(bb);
 255
 256         FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
 257                 kill_dominated_stores(bb);
 258         } END_FOR_EACH_PTR_REVERSE(bb);
 259
 260         FOR_EACH_PTR(ep->accesses, pseudo) {
 261                 struct symbol *var = pseudo->sym;
 262                 unsigned long mod;
 263                 if (!var)
 264                         continue;
 265                 mod = var->ctype.modifiers;
 266                 if (mod & (MOD_VOLATILE | MOD_NONLOCAL | MOD_STATIC))
 267                         continue;
 268                 kill_dead_stores(ep, pseudo, local_pseudo(pseudo));
 269         } END_FOR_EACH_PTR(pseudo);
 270 }