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 #include <string.h>
  37
  38 /* cc65 */
  39 #include "codeent.h"
  40 #include "codeinfo.h"
  41 #include "coptsub.h"
  42
  43
  44
  45 /*****************************************************************************/
  46 /*                           Optimize subtractions                           */
  47 /*****************************************************************************/
  48
  49
  50
  51 unsigned OptSub1 (CodeSeg* S)
  52 /* Search for the sequence
  53  *
  54  *      sbc     ...
  55  *      bcs     L
  56  *      dex
  57  * L:
  58  *
  59  * and remove the handling of the high byte if X is not used later.
  60  */
  61 {
  62     unsigned Changes = 0;
  63
  64     /* Walk over the entries */
  65     unsigned I = 0;
  66     while (I < CS_GetEntryCount (S)) {
  67
  68         CodeEntry* L[3];
  69
  70         /* Get next entry */
  71         CodeEntry* E = CS_GetEntry (S, I);
  72
  73         /* Check for the sequence */
  74         if (E->OPC == OP65_SBC                               &&
  75             CS_GetEntries (S, L, I+1, 3)                     &&
  76             (L[0]->OPC == OP65_BCS || L[0]->OPC == OP65_JCS) &&
  77             L[0]->JumpTo != 0                                &&
  78             !CE_HasLabel (L[0])                              &&
  79             L[1]->OPC == OP65_DEX                            &&
  80             !CE_HasLabel (L[1])                              &&
  81             L[0]->JumpTo->Owner == L[2]                      &&
  82             !RegXUsed (S, I+3)) {
  83
  84             /* Remove the bcs/dex */
  85             CS_DelEntries (S, I+1, 2);
  86
  87             /* Remember, we had changes */
  88             ++Changes;
  89
  90         }
  91
  92         /* Next entry */
  93         ++I;
  94
  95     }
  96
  97     /* Return the number of changes made */
  98     return Changes;
  99 }
 100
 101
 102
 103 unsigned OptSub2 (CodeSeg* S)
 104 /* Search for the sequence
 105  *
 106  *      lda     xx
 107  *      sec
 108  *      sta     tmp1
 109  *      lda     yy
 110  *      sbc     tmp1
 111  *      sta     yy
 112  *
 113  * and replace it by
 114  *
 115  *      sec
 116  *      lda     yy
 117  *      sbc     xx
 118  *      sta     yy
 119  */
 120 {
 121     unsigned Changes = 0;
 122
 123     /* Walk over the entries */
 124     unsigned I = 0;
 125     while (I < CS_GetEntryCount (S)) {
 126
 127         CodeEntry* L[5];
 128
 129         /* Get next entry */
 130         CodeEntry* E = CS_GetEntry (S, I);
 131
 132         /* Check for the sequence */
 133         if (E->OPC == OP65_LDA                             &&
 134             CS_GetEntries (S, L, I+1, 5)                   &&
 135             L[0]->OPC == OP65_SEC                          &&
 136             !CE_HasLabel (L[0])                            &&
 137             L[1]->OPC == OP65_STA                          &&
 138             strcmp (L[1]->Arg, "tmp1") == 0                &&
 139             !CE_HasLabel (L[1])                            &&
 140             L[2]->OPC == OP65_LDA                          &&
 141             !CE_HasLabel (L[2])                            &&
 142             L[3]->OPC == OP65_SBC                          &&
 143             strcmp (L[3]->Arg, "tmp1") == 0                &&
 144             !CE_HasLabel (L[3])                            &&
 145             L[4]->OPC == OP65_STA                          &&
 146             strcmp (L[4]->Arg, L[2]->Arg) == 0             &&
 147             !CE_HasLabel (L[4])) {
 148
 149             /* Remove the store to tmp1 */
 150             CS_DelEntry (S, I+2);
 151
 152             /* Remove the subtraction */
 153             CS_DelEntry (S, I+3);
 154
 155             /* Move the lda to the position of the subtraction and change the
 156              * op to SBC.
 157              */
 158             CS_MoveEntry (S, I, I+3);
 159             CE_ReplaceOPC (E, OP65_SBC);
 160
 161             /* If the sequence head had a label, move this label back to the
 162              * head.
 163              */
 164             if (CE_HasLabel (E)) {
 165                 CS_MoveLabels (S, E, L[0]);
 166             }
 167
 168             /* Remember, we had changes */
 169             ++Changes;
 170
 171         }
 172
 173         /* Next entry */
 174         ++I;
 175
 176     }
 177
 178     /* Return the number of changes made */
 179     return Changes;
 180 }
 181
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 184