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From: Bernhard Reutner-Fischer <aldot@gcc.gnu.org>
Date: Tue, 1 Nov 2011 18:25:08 +0100
Subject: [PATCH] flatten switch-stmt into if-else chain for -Os
This is 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
Signed-off-by: Robert Schwebel <r.schwebel@pengutronix.de>
---
gcc/stmt.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/gcc/stmt.c b/gcc/stmt.c
index 93d643a..7bf3c04 100644
--- a/gcc/stmt.c
+++ b/gcc/stmt.c
@@ -2397,7 +2397,13 @@ expand_case (gimple stmt)
default code is emitted. */
use_cost_table = 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);
if (default_label)
emit_jump (default_label);
@@ -2965,6 +2971,7 @@ emit_case_nodes (rtx index, case_node_ptr node, rtx default_label,
{
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,
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