Original patch from gentoo: gentoo/src/patchsets/gcc/4.3.1/gentoo/18_all_904-flatten-switch-stmt-00.patch

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"

diff -durN gcc-4.3.1.orig/gcc/stmt.c gcc-4.3.1/gcc/stmt.c

--- gcc-4.3.1.orig/gcc/stmt.c	2008-05-09 20:12:13.000000000 +0200

+++ gcc-4.3.1/gcc/stmt.c	2008-06-10 14:57:58.000000000 +0200

@@ -2509,7 +2509,11 @@

 	  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);

 	}

@@ -3067,6 +3071,7 @@

 	    {

 	      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,