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

   1 /*****************************************************************************/
   2 /*                                                                           */
   3 /*                                 codeopt.c                                 */
   4 /*                                                                           */
   5 /*                           Optimizer subroutines                           */
   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 /* b6502 */
  37 #include "codeent.h"
  38 #include "codeopt.h"
  39
  40
  41
  42 /*****************************************************************************/
  43 /*                                   Data                                    */
  44 /*****************************************************************************/
  45
  46
  47
  48 /* Counter for the number of changes in one run. The optimizer process is
  49  * repeated until there are no more changes.
  50  */
  51 static unsigned OptChanges;
  52
  53
  54
  55 /*****************************************************************************/
  56 /*                             Remove dead jumps                             */
  57 /*****************************************************************************/
  58
  59
  60
  61 static void OptDeadJumps (CodeSeg* S)
  62 /* Remove dead jumps (jumps to the next instruction) */
  63 {
  64     CodeEntry* E;
  65     unsigned I;
  66
  67     /* Get the number of entries, bail out if we have less than two entries */
  68     unsigned Count = CollCount (&S->Entries);
  69     if (Count < 2) {
  70         return;
  71     }
  72
  73     /* Walk over all entries minus the last one */
  74     I = 0;
  75     while (I < Count-1) {
  76
  77         /* Get the next entry */
  78         E = CollAt (&S->Entries, I);
  79
  80         /* Check if it's a branch, if it has a local target, and if the target
  81          * is the next instruction.
  82          */
  83         if (E->AM == AM_BRA) {
  84             printf ("BRA on entry %u:\n", I);
  85             if (E->JumpTo) {
  86                 printf ("  JumpTo ok\n");
  87                 if (E->JumpTo->Owner == CollAt (&S->Entries, I+1)) {
  88                     printf ("  Branch to next insn\n");
  89                 }
  90             }
  91         }
  92
  93         if (E->AM == AM_BRA && E->JumpTo && E->JumpTo->Owner == CollAt (&S->Entries, I+1)) {
  94
  95             /* Remember the label */
  96             CodeLabel* L = E->JumpTo;
  97
  98             /* Jump to next instruction, remove it */
  99             unsigned Remaining = RemoveLabelRef (L, E);
 100             CollDelete (&S->Entries, I);
 101             FreeCodeEntry (E);
 102             --Count;
 103
 104             /* If the label has no more references, remove it */
 105             if (Remaining == 0) {
 106                 CollDeleteItem (&L->Owner->Labels, L);
 107                 FreeCodeLabel (L);
 108             }
 109
 110             /* Remember we had changes */
 111             ++OptChanges;
 112
 113         } else {
 114
 115             /* Next entry */
 116             ++I;
 117
 118         }
 119     }
 120 }
 121
 122
 123
 124 /*****************************************************************************/
 125 /*                                   Code                                    */
 126 /*****************************************************************************/
 127
 128
 129
 130 void RunOpt (CodeSeg* S)
 131 /* Run the optimizer */
 132 {
 133     printf ("Optimize\n");
 134
 135     /* Repeat all steps until there are no more changes */
 136     do {
 137
 138         /* Reset the number of changes */
 139         OptChanges = 0;
 140
 141         OptDeadJumps (S);
 142
 143     } while (OptChanges > 0);
 144 }
 145
 146
 147