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 "flow.h"
  18
  19 static int find_dominating_parents(pseudo_t pseudo, struct instruction *insn,
  20         struct basic_block *bb, unsigned long generation, struct pseudo_list **dominators,
  21         int local, int loads)
  22 {
  23         struct basic_block *parent;
  24
  25         if (bb_list_size(bb->parents) > 1)
  26                 loads = 0;
  27         FOR_EACH_PTR(bb->parents, parent) {
  28                 struct instruction *one;
  29                 struct instruction *br;
  30                 pseudo_t phi;
  31
  32                 FOR_EACH_PTR_REVERSE(parent->insns, one) {
  33                         int dominance;
  34                         if (one == insn)
  35                                 goto no_dominance;
  36                         dominance = dominates(pseudo, insn, one, local);
  37                         if (dominance < 0) {
  38                                 if (one->opcode == OP_LOAD)
  39                                         continue;
  40                                 return 0;
  41                         }
  42                         if (!dominance)
  43                                 continue;
  44                         if (one->opcode == OP_LOAD && !loads)
  45                                 continue;
  46                         goto found_dominator;
  47                 } END_FOR_EACH_PTR_REVERSE(one);
  48 no_dominance:
  49                 if (parent->generation == generation)
  50                         continue;
  51                 parent->generation = generation;
  52
  53                 if (!find_dominating_parents(pseudo, insn, parent, generation, dominators, local, loads))
  54                         return 0;
  55                 continue;
  56
  57 found_dominator:
  58                 br = delete_last_instruction(&parent->insns);
  59                 phi = alloc_phi(parent, one->target, one->size);
  60                 phi->ident = phi->ident ? : one->target->ident;
  61                 add_instruction(&parent->insns, br);
  62                 use_pseudo(phi, add_pseudo(dominators, phi));
  63         } END_FOR_EACH_PTR(parent);
  64         return 1;
  65 }
  66
  67 static inline int address_taken(pseudo_t pseudo)
  68 {
  69         pseudo_t *usep;
  70         FOR_EACH_PTR(pseudo->users, usep) {
  71                 struct instruction *insn = container(usep, struct instruction, src);
  72                 if (insn->bb && insn->opcode == OP_SYMADDR)
  73                         return 1;
  74         } END_FOR_EACH_PTR(usep);
  75         return 0;
  76 }
  77
  78 static int local_pseudo(pseudo_t pseudo)
  79 {
  80         return pseudo->type == PSEUDO_SYM
  81                 && !(pseudo->sym->ctype.modifiers & (MOD_STATIC | MOD_NONLOCAL))
  82                 && !address_taken(pseudo);
  83 }
  84
  85 static void simplify_loads(struct basic_block *bb)
  86 {
  87         struct instruction *insn;
  88
  89         FOR_EACH_PTR_REVERSE(bb->insns, insn) {
  90                 if (!insn->bb)
  91                         continue;
  92                 if (insn->opcode == OP_LOAD) {
  93                         struct instruction *dom;
  94                         pseudo_t pseudo = insn->src;
  95                         int local = local_pseudo(pseudo);
  96                         struct pseudo_list *dominators;
  97                         unsigned long generation;
  98
  99                         RECURSE_PTR_REVERSE(insn, dom) {
 100                                 int dominance;
 101                                 if (!dom->bb)
 102                                         continue;
 103                                 dominance = dominates(pseudo, insn, dom, local);
 104                                 if (dominance) {
 105                                         /* possible partial dominance? */
 106                                         if (dominance < 0)  {
 107                                                 if (dom->opcode == OP_LOAD)
 108                                                         continue;
 109                                                 goto next_load;
 110                                         }
 111                                         /* Yeehaa! Found one! */
 112                                         convert_load_instruction(insn, dom->target);
 113                                         goto next_load;
 114                                 }
 115                         } END_FOR_EACH_PTR_REVERSE(dom);
 116
 117                         /* Ok, go find the parents */
 118                         generation = ++bb_generation;
 119                         bb->generation = generation;
 120                         dominators = NULL;
 121                         if (find_dominating_parents(pseudo, insn, bb, generation, &dominators, local, 1)) {
 122                                 /* This happens with initial assignments to structures etc.. */
 123                                 if (!dominators) {
 124                                         if (local) {
 125                                                 assert(pseudo->type != PSEUDO_ARG);
 126                                                 convert_load_instruction(insn, value_pseudo(0));
 127                                         }
 128                                         goto next_load;
 129                                 }
 130                                 rewrite_load_instruction(insn, dominators);
 131                         }
 132                 }
 133 next_load:
 134                 /* Do the next one */;
 135         } END_FOR_EACH_PTR_REVERSE(insn);
 136 }
 137
 138 static void kill_store(struct instruction *insn)
 139 {
 140         if (insn) {
 141                 insn->bb = NULL;
 142                 insn->opcode = OP_SNOP;
 143                 kill_use(&insn->target);
 144         }
 145 }
 146
 147 static void kill_dominated_stores(struct basic_block *bb)
 148 {
 149         struct instruction *insn;
 150
 151         FOR_EACH_PTR_REVERSE(bb->insns, insn) {
 152                 if (!insn->bb)
 153                         continue;
 154                 if (insn->opcode == OP_STORE) {
 155                         struct instruction *dom;
 156                         pseudo_t pseudo = insn->src;
 157                         int local = local_pseudo(pseudo);
 158
 159                         RECURSE_PTR_REVERSE(insn, dom) {
 160                                 int dominance;
 161                                 if (!dom->bb)
 162                                         continue;
 163                                 dominance = dominates(pseudo, insn, dom, local);
 164                                 if (dominance) {
 165                                         /* possible partial dominance? */
 166                                         if (dominance < 0)
 167                                                 goto next_store;
 168                                         if (dom->opcode == OP_LOAD)
 169                                                 goto next_store;
 170                                         /* Yeehaa! Found one! */
 171                                         kill_store(dom);
 172                                 }
 173                         } END_FOR_EACH_PTR_REVERSE(dom);
 174
 175                         /* Ok, we should check the parents now */
 176                 }
 177 next_store:
 178                 /* Do the next one */;
 179         } END_FOR_EACH_PTR_REVERSE(insn);
 180 }
 181
 182 void simplify_memops(struct entrypoint *ep)
 183 {
 184         struct basic_block *bb;
 185
 186         FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
 187                 simplify_loads(bb);
 188         } END_FOR_EACH_PTR_REVERSE(bb);
 189
 190         FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
 191                 kill_dominated_stores(bb);
 192         } END_FOR_EACH_PTR_REVERSE(bb);
 193 }