http://gcc.gnu.org/ml/gcc-patches/2007-04/msg00927.html Hi, The attached patch makes sure that we create smaller object code for simple switch statements. We just make sure to flatten the switch statement into an if-else chain, basically. This fixes a size-regression as compared to gcc-3.4, as can be seen below. 2007-04-15 Bernhard Fischer <..> * stmt.c (expand_case): Do not create a complex binary tree when optimizing for size but rather use the simple ordered list. (emit_case_nodes): do not emit jumps to the default_label when optimizing for size. Not regtested so far. Comments? Attached is the test switch.c mentioned below. $ 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 gcc-$i -DCHAIN -Os -o switch-CHAIN-$i.o -c switch.c ;done $ 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 gcc-$i -UCHAIN -Os -o switch-$i.o -c switch.c ;done $ size switch-*.o text data bss dec hex filename 169 0 0 169 a9 switch-2.95.o 115 0 0 115 73 switch-3.3.o 103 0 0 103 67 switch-3.4.o 124 0 0 124 7c switch-4.0.o 124 0 0 124 7c switch-4.1.o 124 0 0 124 7c switch-4.2.orig-HEAD.o 95 0 0 95 5f switch-4.3-HEAD.o 124 0 0 124 7c switch-4.3.orig-HEAD.o 166 0 0 166 a6 switch-CHAIN-2.95.o 111 0 0 111 6f switch-CHAIN-3.3.o 95 0 0 95 5f switch-CHAIN-3.4.o 95 0 0 95 5f switch-CHAIN-4.0.o 95 0 0 95 5f switch-CHAIN-4.1.o 95 0 0 95 5f switch-CHAIN-4.2.orig-HEAD.o 95 0 0 95 5f switch-CHAIN-4.3-HEAD.o 95 0 0 95 5f switch-CHAIN-4.3.orig-HEAD.o Content-Type: text/x-diff; charset=us-ascii Content-Disposition: attachment; filename="gcc-4.3.gcc-flatten-switch-stmt.00.diff" Index: gcc-4.2.0/gcc/stmt.c =================================================================== --- gcc-4.2.0.orig/gcc/stmt.c (revision 123843) +++ gcc-4.2.0/gcc/stmt.c (working copy) @@ -2517,7 +2517,11 @@ expand_case (tree exp) use_cost_table = (TREE_CODE (orig_type) != ENUMERAL_TYPE && estimate_case_costs (case_list)); - balance_case_nodes (&case_list, NULL); + /* When optimizing for size, we want a straight list to avoid + jumps as much as possible. This basically creates an if-else + chain. */ + if (!optimize_size) + balance_case_nodes (&case_list, NULL); emit_case_nodes (index, case_list, default_label, index_type); emit_jump (default_label); } @@ -3075,6 +3079,7 @@ emit_case_nodes (rtx index, case_node_pt { if (!node_has_low_bound (node, index_type)) { + if (!optimize_size) /* don't jl to the .default_label. */ emit_cmp_and_jump_insns (index, convert_modes (mode, imode, Content-Type: text/x-csrc; charset=us-ascii Content-Disposition: attachment; filename="switch.c" int commutative_tree_code (int code) { #define CASE(val, ret) case val:/* __asm__("# val="#val ",ret="#ret);*/ return ret; #ifndef CHAIN switch (code) { # if 1 CASE(1,3) CASE(3,2) CASE(5,8) CASE(7,1) CASE(33,4) CASE(44,9) CASE(55,10) CASE(66,-1) CASE(77,99) CASE(666,0) # else case 1: return 3; case 3: return 2; case 5: return 8; case 7: return 1; case 33: return 4; case 44: return 9; case 55: return 10; case 66: return -1; case 77: return 99; case 666: return 0; # endif default: break; } return 4711; #else if (code == 1) return 3; else if (code == 3) return 2; else if (code == 5) return 8; else if (code == 7) return 1; else if (code == 33) return 4; else if (code == 44) return 9; else if (code == 55) return 10; else if (code == 66) return -1; else if (code == 77) return 99; else if (code == 666) return 0; else return 4711; #endif } --AhhlLboLdkugWU4S--