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   1 /*****************************************************************************/
   2 /*                                                                           */
   3 /*                                coptshift.h                                */
   4 /*                                                                           */
   5 /*                              Optimize shifts                              */
   6 /*                                                                           */
   7 /*                                                                           */
   8 /*                                                                           */
   9 /* (C) 2001-2012, Ullrich von Bassewitz                                      */
  10 /*                Roemerstrasse 52                                           */
  11 /*                D-70794 Filderstadt                                        */
  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 #ifndef COPTSHIFT_H
  37 #define COPTSHIFT_H
  38
  39
  40
  41 /* cc65 */
  42 #include "codeseg.h"
  43
  44
  45
  46 /*****************************************************************************/
  47 /*                              Optimize shifts                              */
  48 /*****************************************************************************/
  49
  50
  51
  52 unsigned OptShift1 (CodeSeg* S);
  53 /* A call to the shlaxN routine may get replaced by one or more asl insns
  54 ** if the value of X is not used later. If X is used later, but it is zero
  55 ** on entry and it's a shift by one, it may get replaced by:
  56 **
  57 **      asl     a
  58 **      bcc     L1
  59 **      inx
  60 **  L1:
  61 */
  62
  63 unsigned OptShift2 (CodeSeg* S);
  64 /* The sequence
  65 **
  66 **      bpl     L
  67 **      dex
  68 ** L:   jsr     asraxN
  69 **
  70 ** might be replaced by N copies of
  71 **
  72 **      cmp     #$80
  73 **      ror     a
  74 **
  75 ** if X is not used later (X is assumed to be zero on entry).
  76 */
  77
  78 unsigned OptShift3 (CodeSeg* S);
  79 /* The sequence
  80 **
  81 **      bcc     L
  82 **      inx
  83 ** L:   jsr     shrax1
  84 **
  85 ** may get replaced by
  86 **
  87 **      ror     a
  88 **
  89 ** if X is zero on entry and unused later. For shift counts > 1, more
  90 **
  91 **      shr     a
  92 **
  93 ** must be added.
  94 */
  95
  96 unsigned OptShift4 (CodeSeg* S);
  97 /* Calls to the asraxN or shraxN routines may get replaced by one or more lsr
  98 ** insns if the value of X is zero.
  99 */
 100
 101 unsigned OptShift5 (CodeSeg* S);
 102 /* Search for the sequence
 103 **
 104 **      lda     xxx
 105 **      ldx     yyy
 106 **      jsr     aslax1/asrax1/shlax1/shrax1
 107 **      sta     aaa
 108 **      stx     bbb
 109 **
 110 ** and replace it by
 111 **
 112 **      lda     xxx
 113 **      asl     a
 114 **      sta     aaa
 115 **      lda     yyy
 116 **      rol     a
 117 **      sta     bbb
 118 **
 119 ** or similar, provided that a/x is not used later
 120 */
 121
 122 unsigned OptShift6 (CodeSeg* S);
 123 /* Inline the shift subroutines. */
 124
 125
 126
 127 /* End of coptshift.h */
 128
 129 #endif