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--