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(insn, phi, add_pseudo(dominators, phi));
  63         } END_FOR_EACH_PTR(parent);
  64         return 1;
  65 }
  66
  67 static int address_taken(pseudo_t pseudo)
  68 {
  69         struct pseudo_user *pu;
  70         FOR_EACH_PTR(pseudo->users, pu) {
  71                 struct instruction *insn = pu->insn;
  72                 if (insn->bb && (insn->opcode != OP_LOAD && insn->opcode != OP_STORE))
  73                         return 1;
  74         } END_FOR_EACH_PTR(pu);
  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                         /* Check for illegal offsets.. */
 100                         check_access(insn);
 101
 102                         RECURSE_PTR_REVERSE(insn, dom) {
 103                                 int dominance;
 104                                 if (!dom->bb)
 105                                         continue;
 106                                 dominance = dominates(pseudo, insn, dom, local);
 107                                 if (dominance) {
 108                                         /* possible partial dominance? */
 109                                         if (dominance < 0)  {
 110                                                 if (dom->opcode == OP_LOAD)
 111                                                         continue;
 112                                                 goto next_load;
 113                                         }
 114                                         /* Yeehaa! Found one! */
 115                                         convert_load_instruction(insn, dom->target);
 116                                         goto next_load;
 117                                 }
 118                         } END_FOR_EACH_PTR_REVERSE(dom);
 119
 120                         /* OK, go find the parents */
 121                         generation = ++bb_generation;
 122                         bb->generation = generation;
 123                         dominators = NULL;
 124                         if (find_dominating_parents(pseudo, insn, bb, generation, &dominators, local, 1)) {
 125                                 /* This happens with initial assignments to structures etc.. */
 126                                 if (!dominators) {
 127                                         if (local) {
 128                                                 assert(pseudo->type != PSEUDO_ARG);
 129                                                 convert_load_instruction(insn, value_pseudo(0));
 130                                         }
 131                                         goto next_load;
 132                                 }
 133                                 rewrite_load_instruction(insn, dominators);
 134                         }
 135                 }
 136 next_load:
 137                 /* Do the next one */;
 138         } END_FOR_EACH_PTR_REVERSE(insn);
 139 }
 140
 141 static void kill_store(struct instruction *insn)
 142 {
 143         if (insn) {
 144                 insn->bb = NULL;
 145                 insn->opcode = OP_SNOP;
 146                 kill_use(&insn->target);
 147         }
 148 }
 149
 150 static void kill_dominated_stores(struct basic_block *bb)
 151 {
 152         struct instruction *insn;
 153
 154         FOR_EACH_PTR_REVERSE(bb->insns, insn) {
 155                 if (!insn->bb)
 156                         continue;
 157                 if (insn->opcode == OP_STORE) {
 158                         struct instruction *dom;
 159                         pseudo_t pseudo = insn->src;
 160                         int local = local_pseudo(pseudo);
 161
 162                         RECURSE_PTR_REVERSE(insn, dom) {
 163                                 int dominance;
 164                                 if (!dom->bb)
 165                                         continue;
 166                                 dominance = dominates(pseudo, insn, dom, local);
 167                                 if (dominance) {
 168                                         /* possible partial dominance? */
 169                                         if (dominance < 0)
 170                                                 goto next_store;
 171                                         if (dom->opcode == OP_LOAD)
 172                                                 goto next_store;
 173                                         /* Yeehaa! Found one! */
 174                                         kill_store(dom);
 175                                 }
 176                         } END_FOR_EACH_PTR_REVERSE(dom);
 177
 178                         /* OK, we should check the parents now */
 179                 }
 180 next_store:
 181                 /* Do the next one */;
 182         } END_FOR_EACH_PTR_REVERSE(insn);
 183 }
 184
 185 void simplify_memops(struct entrypoint *ep)
 186 {
 187         struct basic_block *bb;
 188
 189         FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
 190                 simplify_loads(bb);
 191         } END_FOR_EACH_PTR_REVERSE(bb);
 192
 193         FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
 194                 kill_dominated_stores(bb);
 195         } END_FOR_EACH_PTR_REVERSE(bb);
 196 }