doc/sparc/B

   1 .In
   2 .SH
   3 B. IMPLEMENTATION
   4 .SH
   5 B.1. Excerpts from the non-optimized EM_table
   6 .PP
   7 Even though the non-optimized version of the EM_table is relatively
   8 straight-forward, examples have never hurt anybody.
   9 One of the simplest instructions is the \*(Siloc\*(So, which appears in
  10 our EM_table as follows:
  11 .DS
  12 \f6
  13 .TA 8 16 24 32 40 48 56 64
  14 C_loc   ==>     "set    $1, T1";
  15                 "dec    4, SP";
  16                 "st     T1, [SP]".
  17 \f1
  18 .DE
  19 Just as \*(SiSP\*(So is an alias for \*(Si%l0\*(So, \*(SiT1\*(So is
  20 an alias for \*(Si%g1\*(So.
  21 A little more complex is the \*(Siadi\*(So which performs integer
  22 addition.
  23 .DS
  24 \f6
  25 C_adi   ==>     "ld     [SP], T1";
  26                 "ld     [SP+4], T2";
  27                 "add    T1, T2, T3";
  28                 "st     T3, [SP+4];
  29                 "inc    4, SP".
  30 \f1
  31 .DE
  32 We could go on with even more complex instructions, but since that would
  33 not contribute to anything the reader is referred to the implementation
  34 for more details.
  35 .SH
  36 B.2. Excerpts from the optimized EM_table
  37 .PP
  38 The optimized EM_table uses the cache primitives mentioned in chapter 4.
  39 This means that the \*(Siloc\*(So this time appears as
  40 .DS
  41 \f6
  42 C_loc   ==>     push_const($1).
  43 \f1
  44 .DE
  45 The \*(Silol\*(So can now be written as
  46 .DS
  47 \f6
  48 C_lol   ==>     push_reg(LB);
  49                 inc_tos($1);
  50                 push_const(4);
  51                 C_los(4).
  52 \f1
  53 .DE
  54 Due to the law of conservation of misery somebody has to do the dirty work.
  55 In this case, it is the \*(Silos\*(So. To show just a small part of
  56 the implementation of the \*(Silos\*(So:
  57 .DS
  58 \f6
  59 C_los   $1 == 4 ==>
  60                 if (type_of_tos() == T_cst) {
  61                         arith size;
  62                         const_str_t n;
  63
  64                         size= pop_const();
  65                         if (size <= 4) {
  66                                 reg_t a;
  67                                 reg_t a;
  68                                 char *LD;
  69
  70                                 switch (size) {
  71                                 case 1: LD = "ldub"; break;
  72                                 case 2: LD = "lduh"; break;
  73                                 case 4: LD = "ld"; break;
  74                                 default:        arg_error("C_los", size);
  75                                 }
  76                                 a = pop_reg_c13(n);
  77                                 b = alloc_reg();
  78                                 "$LD    [$a+$n], $b";
  79                                 push_reg(b);
  80                                 free_reg(a);
  81                         } else ...
  82 \f1
  83 .DE
  84 For the full implementation, the reader is again referred to the actual
  85 implementation. Just to show how other instructions are affected
  86 by the optimization we will show that implementation of the \*(Sitge\*(So
  87 instruction:
  88 .DS
  89 \f6
  90 C_tge   ==>     {
  91                         reg_t a;
  92                         reg_t b;
  93
  94                         a = pop_reg();
  95                         b = alloc_reg();
  96                         "       tst     $a";
  97                         "       bge,a   1f";
  98                         "       mov     1, $b";         /* delay slot */
  99                         "       set     0, $b";
 100                         "1:";
 101                         free_reg(a);
 102                         push_reg(b);
 103                 }.
 104
 105 \f1
 106 .DE
 107 .SH
 108 .bp
 109 CREDITS
 110 .PP
 111 In order of appearance:
 112 .TS
 113 center;
 114 r c l.
 115 Original idea   -       Dick Grune
 116 Design & implementation -       Philip Homburg
 117         -       Raymond Michiels
 118 Tutor   -       Dick Grune
 119 Assistant Tutor -       Ceriel Jacobs
 120 Proofreading    -       Dick Grune
 121         -       Hans van Eck
 122 .TE
 123 .SH
 124 REFERENCES
 125 .PP
 126 .[
 127 $LIST$
 128 .]