[patch] tree-cfg.c: Speed up thread_jumps() - Part 1

[Kazu Hirata <kazu at cs dot umass dot edu>]

Hi,

Attached is a patch to speed up thread_jumps().

Now we have no unreachable block before and after calling
thread_jumps().  Even within thread_jumps(), unreachable blocks are
removed as they arise.

So basically

  /* Don't waste time on unreachable blocks.  */
  if (EDGE_COUNT (bb->preds) == 0)
    continue;

does not trigger except for ENTRY_BLOCK_PTR.  We don't want to perform
jump threading on ENTRY_BLOCK_PTR anyway, so I can change

  FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb)

to

  FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR->nextbb, EXIT_BLOCK_PTR, next_bb)

which is just the same as

  FOR_EACH_BB (bb)

The patch removes the useless if and changes FOR_BB_BETWEEN to
FOR_EACH_BB.

Tested on i686-pc-linux-gnu on top of

http://gcc.gnu.org/ml/gcc-patches/2004-10/msg00169.html
http://gcc.gnu.org/ml/gcc-patches/2004-10/msg00186.html

OK to apply?

Kazu Hirata

2004-10-04  Kazu Hirata  <kazu@cs.umass.edu>

	* tree-cfg.c (thread_jumps): Iterate with FOR_EACH_BB instead
	of FOR_BB_BETWEEN.  Remove a useless check for unreachable
	blocks.

Index: tree-cfg.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-cfg.c,v
retrieving revision 2.64
diff -c -r2.64 tree-cfg.c
*** tree-cfg.c	2 Oct 2004 12:47:10 -0000	2.64
--- tree-cfg.c	3 Oct 2004 19:31:22 -0000
***************
*** 3835,3841 ****
  /* Thread jumps over empty statements.
  
     This code should _not_ thread over obviously equivalent conditions
!    as that requires nontrivial updates to the SSA graph.  */
     
  static bool
  thread_jumps (void)
--- 3835,3845 ----
  /* Thread jumps over empty statements.
  
     This code should _not_ thread over obviously equivalent conditions
!    as that requires nontrivial updates to the SSA graph.
! 
!    As a precondition, we require that all basic blocks be reachable.
!    That is, there should be no opportunities left for
!    delete_unreachable_blocks().  */
     
  static bool
  thread_jumps (void)
***************
*** 3849,3866 ****
    FOR_EACH_BB (bb)
      bb_ann (bb)->forwardable = 1;
  
!   FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb)
      {
        edge_iterator ei;
  
!       /* Don't waste time on unreachable blocks.  */
!       if (EDGE_COUNT (bb->preds) == 0)
! 	continue;
! 
!       /* Nor on forwarders.  */
        if (tree_forwarder_block_p (bb))
  	continue;
!       
        /* This block is now part of a forwarding path, mark it as not
  	 forwardable so that we can detect loops.  This bit will be
  	 reset below.  */
--- 3853,3866 ----
    FOR_EACH_BB (bb)
      bb_ann (bb)->forwardable = 1;
  
!   FOR_EACH_BB (bb)
      {
        edge_iterator ei;
  
!       /* Don't waste time on forwarders.  */
        if (tree_forwarder_block_p (bb))
  	continue;
! 
        /* This block is now part of a forwarding path, mark it as not
  	 forwardable so that we can detect loops.  This bit will be
  	 reset below.  */