toolchain/gcc/patches/4.2.4/904-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-4.2.3/gcc/stmt.c
  51 ===================================================================
  52 --- gcc-4.2.3.orig/gcc/stmt.c   2007-09-01 17:28:30.000000000 +0200
  53 +++ gcc-4.2.3/gcc/stmt.c        2008-05-21 13:45:59.137288494 +0200
  54 @@ -2511,7 +2511,11 @@
  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 @@ -3069,6 +3073,7 @@
  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,