git.sur5r.net Git - cc65/blob - src/cc65/coptsub.c

   1 /*****************************************************************************/
   2 /*                                                                           */
   3 /*                                 coptsub.c                                 */
   4 /*                                                                           */
   5 /*                      Optimize subtraction sequences                       */
   6 /*                                                                           */
   7 /*                                                                           */
   8 /*                                                                           */
   9 /* (C) 2001      Ullrich von Bassewitz                                       */
  10 /*               Wacholderweg 14                                             */
  11 /*               D-70597 Stuttgart                                           */
  12 /* EMail:        uz@cc65.org                                                 */
  13 /*                                                                           */
  14 /*                                                                           */
  15 /* This software is provided 'as-is', without any expressed or implied       */
  16 /* warranty.  In no event will the authors be held liable for any damages    */
  17 /* arising from the use of this software.                                    */
  18 /*                                                                           */
  19 /* Permission is granted to anyone to use this software for any purpose,     */
  20 /* including commercial applications, and to alter it and redistribute it    */
  21 /* freely, subject to the following restrictions:                            */
  22 /*                                                                           */
  23 /* 1. The origin of this software must not be misrepresented; you must not   */
  24 /*    claim that you wrote the original software. If you use this software   */
  25 /*    in a product, an acknowledgment in the product documentation would be  */
  26 /*    appreciated but is not required.                                       */
  27 /* 2. Altered source versions must be plainly marked as such, and must not   */
  28 /*    be misrepresented as being the original software.                      */
  29 /* 3. This notice may not be removed or altered from any source              */
  30 /*    distribution.                                                          */
  31 /*                                                                           */
  32 /*****************************************************************************/
  33
  34
  35
  36 /* cc65 */
  37 #include "codeent.h"
  38 #include "codeinfo.h"
  39 #include "coptsub.h"
  40
  41
  42
  43 /*****************************************************************************/
  44 /*                           Optimize subtractions                           */
  45 /*****************************************************************************/
  46
  47
  48
  49 unsigned OptSub1 (CodeSeg* S)
  50 /* Search for the sequence
  51  *
  52  *      sbc     ...
  53  *      bcs     L
  54  *      dex
  55  * L:
  56  *
  57  * and remove the handling of the high byte if X is not used later.
  58  */
  59 {
  60     unsigned Changes = 0;
  61
  62     /* Walk over the entries */
  63     unsigned I = 0;
  64     while (I < CS_GetEntryCount (S)) {
  65
  66         CodeEntry* L[3];
  67
  68         /* Get next entry */
  69         CodeEntry* E = CS_GetEntry (S, I);
  70
  71         /* Check for the sequence */
  72         if (E->OPC == OP65_SBC                               &&
  73             CS_GetEntries (S, L, I+1, 3)                     &&
  74             (L[0]->OPC == OP65_BCS || L[0]->OPC == OP65_JCS) &&
  75             L[0]->JumpTo != 0                                &&
  76             !CE_HasLabel (L[0])                              &&
  77             L[1]->OPC == OP65_DEX                            &&
  78             !CE_HasLabel (L[1])                              &&
  79             L[0]->JumpTo->Owner == L[2]                      &&
  80             !RegXUsed (S, I+3)) {
  81
  82             /* Remove the bcs/dex */
  83             CS_DelEntries (S, I+1, 2);
  84
  85             /* Remember, we had changes */
  86             ++Changes;
  87
  88         }
  89
  90         /* Next entry */
  91         ++I;
  92
  93     }
  94
  95     /* Return the number of changes made */
  96     return Changes;
  97 }
  98
  99
 100
 101 unsigned OptSub2 (CodeSeg* S)
 102 /* Search for the sequence
 103  *
 104  *      lda     xx
 105  *      sec
 106  *      sta     tmp1
 107  *      lda     yy
 108  *      sbc     tmp1
 109  *      sta     yy
 110  *
 111  * and replace it by
 112  *
 113  *      sec
 114  *      lda     yy
 115  *      sbc     xx
 116  *      sta     yy
 117  */
 118 {
 119     unsigned Changes = 0;
 120
 121     /* Walk over the entries */
 122     unsigned I = 0;
 123     while (I < CS_GetEntryCount (S)) {
 124
 125         CodeEntry* L[5];
 126
 127         /* Get next entry */
 128         CodeEntry* E = CS_GetEntry (S, I);
 129
 130         /* Check for the sequence */
 131         if (E->OPC == OP65_LDA                             &&
 132             !CS_RangeHasLabel (S, I+1, 5)                  &&
 133             CS_GetEntries (S, L, I+1, 5)                   &&
 134             L[0]->OPC == OP65_SEC                          &&
 135             L[1]->OPC == OP65_STA                          &&
 136             strcmp (L[1]->Arg, "tmp1") == 0                &&
 137             L[2]->OPC == OP65_LDA                          &&
 138             L[3]->OPC == OP65_SBC                          &&
 139             strcmp (L[3]->Arg, "tmp1") == 0                &&
 140             L[4]->OPC == OP65_STA                          &&
 141             strcmp (L[4]->Arg, L[2]->Arg) == 0) {
 142
 143             /* Remove the store to tmp1 */
 144             CS_DelEntry (S, I+2);
 145
 146             /* Remove the subtraction */
 147             CS_DelEntry (S, I+3);
 148
 149             /* Move the lda to the position of the subtraction and change the
 150              * op to SBC.
 151              */
 152             CS_MoveEntry (S, I, I+3);
 153             CE_ReplaceOPC (E, OP65_SBC);
 154
 155             /* If the sequence head had a label, move this label back to the
 156              * head.
 157              */
 158             if (CE_HasLabel (E)) {
 159                 CS_MoveLabels (S, E, L[0]);
 160             }
 161
 162             /* Remember, we had changes */
 163             ++Changes;
 164
 165         }
 166
 167         /* Next entry */
 168         ++I;
 169
 170     }
 171
 172     /* Return the number of changes made */
 173     return Changes;
 174 }
 175
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