toolchain/gcc/patches/4.2.2/904-flatten-switch-stmt-00.patch

   1 Hi,
   2
   3 The attached patch makes sure that we create smaller object code for
   4 simple switch statements. We just make sure to flatten the switch
   5 statement into an if-else chain, basically.
   6
   7 This fixes a size-regression as compared to gcc-3.4, as can be seen
   8 below.
   9
  10 2007-04-15  Bernhard Fischer  <..>
  11
  12         * stmt.c (expand_case): Do not create a complex binary tree when
  13         optimizing for size but rather use the simple ordered list.
  14         (emit_case_nodes): do not emit jumps to the default_label when
  15         optimizing for size.
  16
  17 Not regtested so far.
  18 Comments?
  19
  20 Attached is the test switch.c mentioned below.
  21
  22 $ for i in 2.95 3.3 3.4 4.0 4.1 4.2.orig-HEAD 4.3.orig-HEAD 4.3-HEAD;do
  23 gcc-$i  -DCHAIN -Os -o switch-CHAIN-$i.o -c switch.c ;done
  24 $ for i in 2.95 3.3 3.4 4.0 4.1 4.2.orig-HEAD 4.3.orig-HEAD 4.3-HEAD;do
  25 gcc-$i  -UCHAIN -Os -o switch-$i.o -c switch.c ;done
  26
  27 $ size switch-*.o
  28    text    data     bss     dec     hex filename
  29     169       0       0     169      a9 switch-2.95.o
  30     115       0       0     115      73 switch-3.3.o
  31     103       0       0     103      67 switch-3.4.o
  32     124       0       0     124      7c switch-4.0.o
  33     124       0       0     124      7c switch-4.1.o
  34     124       0       0     124      7c switch-4.2.orig-HEAD.o
  35      95       0       0      95      5f switch-4.3-HEAD.o
  36     124       0       0     124      7c switch-4.3.orig-HEAD.o
  37     166       0       0     166      a6 switch-CHAIN-2.95.o
  38     111       0       0     111      6f switch-CHAIN-3.3.o
  39      95       0       0      95      5f switch-CHAIN-3.4.o
  40      95       0       0      95      5f switch-CHAIN-4.0.o
  41      95       0       0      95      5f switch-CHAIN-4.1.o
  42      95       0       0      95      5f switch-CHAIN-4.2.orig-HEAD.o
  43      95       0       0      95      5f switch-CHAIN-4.3-HEAD.o
  44      95       0       0      95      5f switch-CHAIN-4.3.orig-HEAD.o
  45
  46
  47 Content-Type: text/x-diff; charset=us-ascii
  48 Content-Disposition: attachment; filename="gcc-4.3.gcc-flatten-switch-stmt.00.diff"
  49
  50 Index: gcc-4.2.0/gcc/stmt.c
  51 ===================================================================
  52 --- gcc-4.2.0.orig/gcc/stmt.c   (revision 123843)
  53 +++ gcc-4.2.0/gcc/stmt.c        (working copy)
  54 @@ -2517,7 +2517,11 @@ expand_case (tree exp)
  55           use_cost_table
  56             = (TREE_CODE (orig_type) != ENUMERAL_TYPE
  57                && estimate_case_costs (case_list));
  58 -         balance_case_nodes (&case_list, NULL);
  59 +         /* When optimizing for size, we want a straight list to avoid
  60 +            jumps as much as possible. This basically creates an if-else
  61 +            chain.  */
  62 +         if (!optimize_size)
  63 +           balance_case_nodes (&case_list, NULL);
  64           emit_case_nodes (index, case_list, default_label, index_type);
  65           emit_jump (default_label);
  66         }
  67 @@ -3075,6 +3079,7 @@ emit_case_nodes (rtx index, case_node_pt
  68             {
  69               if (!node_has_low_bound (node, index_type))
  70                 {
  71 +                 if (!optimize_size) /* don't jl to the .default_label. */
  72                   emit_cmp_and_jump_insns (index,
  73                                            convert_modes
  74                                            (mode, imode,
  75
  76
  77 Content-Type: text/x-csrc; charset=us-ascii
  78 Content-Disposition: attachment; filename="switch.c"
  79
  80 int
  81 commutative_tree_code (int code)
  82 {
  83 #define CASE(val, ret) case val:/* __asm__("# val="#val ",ret="#ret);*/ return ret;
  84 #ifndef CHAIN
  85   switch (code)
  86     {
  87 # if 1
  88   CASE(1,3)
  89   CASE(3,2)
  90   CASE(5,8)
  91   CASE(7,1)
  92   CASE(33,4)
  93   CASE(44,9)
  94   CASE(55,10)
  95   CASE(66,-1)
  96   CASE(77,99)
  97   CASE(666,0)
  98 # else
  99     case 1:
 100       return 3;
 101     case 3:
 102       return 2;
 103     case 5:
 104       return 8;
 105     case 7:
 106       return 1;
 107     case 33:
 108       return 4;
 109     case 44:
 110       return 9;
 111     case 55:
 112       return 10;
 113     case 66:
 114       return -1;
 115     case 77:
 116       return 99;
 117     case 666:
 118       return 0;
 119 # endif
 120     default:
 121       break;
 122     }
 123   return 4711;
 124
 125 #else
 126    if (code == 1)
 127         return 3;
 128   else if (code == 3)
 129         return 2;
 130   else if (code == 5)
 131         return 8;
 132   else if (code == 7)
 133         return 1;
 134   else if (code == 33)
 135         return 4;
 136   else if (code == 44)
 137         return 9;
 138   else if (code == 55)
 139         return 10;
 140   else if (code == 66)
 141         return -1;
 142   else if (code == 77)
 143         return 99;
 144   else if (code == 666)
 145         return 0;
 146   else
 147         return 4711;
 148 #endif
 149 }
 150
 151
 152 --AhhlLboLdkugWU4S--
 153