1 Original patch from gentoo: gentoo/src/patchsets/gcc/4.3.1/gentoo/18_all_904-flatten-switch-stmt-00.patch
2 http://gcc.gnu.org/ml/gcc-patches/2007-04/msg00927.html
6 The attached patch makes sure that we create smaller object code for
7 simple switch statements. We just make sure to flatten the switch
8 statement into an if-else chain, basically.
10 This fixes a size-regression as compared to gcc-3.4, as can be seen
13 2007-04-15 Bernhard Fischer <..>
15 * stmt.c (expand_case): Do not create a complex binary tree when
16 optimizing for size but rather use the simple ordered list.
17 (emit_case_nodes): do not emit jumps to the default_label when
23 Attached is the test switch.c mentioned below.
25 $ 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
26 gcc-$i -DCHAIN -Os -o switch-CHAIN-$i.o -c switch.c ;done
27 $ 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
28 gcc-$i -UCHAIN -Os -o switch-$i.o -c switch.c ;done
31 text data bss dec hex filename
32 169 0 0 169 a9 switch-2.95.o
33 115 0 0 115 73 switch-3.3.o
34 103 0 0 103 67 switch-3.4.o
35 124 0 0 124 7c switch-4.0.o
36 124 0 0 124 7c switch-4.1.o
37 124 0 0 124 7c switch-4.2.orig-HEAD.o
38 95 0 0 95 5f switch-4.3-HEAD.o
39 124 0 0 124 7c switch-4.3.orig-HEAD.o
40 166 0 0 166 a6 switch-CHAIN-2.95.o
41 111 0 0 111 6f switch-CHAIN-3.3.o
42 95 0 0 95 5f switch-CHAIN-3.4.o
43 95 0 0 95 5f switch-CHAIN-4.0.o
44 95 0 0 95 5f switch-CHAIN-4.1.o
45 95 0 0 95 5f switch-CHAIN-4.2.orig-HEAD.o
46 95 0 0 95 5f switch-CHAIN-4.3-HEAD.o
47 95 0 0 95 5f switch-CHAIN-4.3.orig-HEAD.o
50 Content-Type: text/x-diff; charset=us-ascii
51 Content-Disposition: attachment; filename="gcc-4.3.gcc-flatten-switch-stmt.00.diff"
53 diff -durN gcc-4.3.1.orig/gcc/stmt.c gcc-4.3.1/gcc/stmt.c
54 --- gcc-4.3.1.orig/gcc/stmt.c 2008-05-09 20:12:13.000000000 +0200
55 +++ gcc-4.3.1/gcc/stmt.c 2008-06-10 14:57:58.000000000 +0200
56 @@ -2509,7 +2509,11 @@
58 = (TREE_CODE (orig_type) != ENUMERAL_TYPE
59 && estimate_case_costs (case_list));
60 - balance_case_nodes (&case_list, NULL);
61 + /* When optimizing for size, we want a straight list to avoid
62 + jumps as much as possible. This basically creates an if-else
65 + balance_case_nodes (&case_list, NULL);
66 emit_case_nodes (index, case_list, default_label, index_type);
67 emit_jump (default_label);
71 if (!node_has_low_bound (node, index_type))
73 + if (!optimize_size) /* don't jl to the .default_label. */
74 emit_cmp_and_jump_insns (index,