| 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, |
| 75 | |
