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[patch] tree-cfg.c: Speed up remove_forwarder_block_with_phi.


Hi,

Attached is a patch to speed up remove_forwarder_block_with_phi.

Note that we now make a considerable effort to ensure that a nonlocal
label appears first in a sequence of labels.  Specifically,
stmt_starts_bb_p guarantees this property when CFG is constructed, and
tree_verify_flow_info verifies it at various points in tree
optimizations.

So we should take advantage of this property and simplify a loop that
looks for nonlocal labels.  We can simply look at the very first
statement and see if it's a nonlocal label.

Tested on i686-pc-linux-gnu.  OK to apply?

Kazu Hirata

2005-01-22  Kazu Hirata  <kazu@cs.umass.edu>

	* tree-cfg.c (remove_forwarder_block_with_phi): Look at the
	first label to see if it is a nonlocal label.

Index: tree-cfg.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-cfg.c,v
retrieving revision 2.144
diff -c -d -p -r2.144 tree-cfg.c
*** tree-cfg.c	21 Jan 2005 13:05:02 -0000	2.144
--- tree-cfg.c	21 Jan 2005 14:42:31 -0000
*************** remove_forwarder_block_with_phi (basic_b
*** 4130,4137 ****
  {
    edge succ = EDGE_SUCC (bb, 0);
    basic_block dest = succ->dest;
    basic_block dombb, domdest, dom;
-   block_stmt_iterator bsi;
  
    /* We check for infinite loops already in tree_forwarder_block_p.
       However it may happen that the infinite loop is created
--- 4130,4137 ----
  {
    edge succ = EDGE_SUCC (bb, 0);
    basic_block dest = succ->dest;
+   tree label;
    basic_block dombb, domdest, dom;
  
    /* We check for infinite loops already in tree_forwarder_block_p.
       However it may happen that the infinite loop is created
*************** remove_forwarder_block_with_phi (basic_b
*** 4141,4156 ****
  
    /* If the destination block consists of a nonlocal label, do not
       merge it.  */
!   for (bsi = bsi_start (dest); !bsi_end_p (bsi); bsi_next (&bsi))
!     {
!       tree stmt = bsi_stmt (bsi);
! 
!       if (TREE_CODE (stmt) != LABEL_EXPR)
! 	break;
! 
!       if (DECL_NONLOCAL (LABEL_EXPR_LABEL (stmt)))
! 	return;
!     }
  
    /* Redirect each incoming edge to BB to DEST.  */
    while (EDGE_COUNT (bb->preds) > 0)
--- 4141,4151 ----
  
    /* If the destination block consists of a nonlocal label, do not
       merge it.  */
!   label = first_stmt (dest);
!   if (label
!       && TREE_CODE (label) == LABEL_EXPR
!       && DECL_NONLOCAL (LABEL_EXPR_LABEL (label)))
!     return;
  
    /* Redirect each incoming edge to BB to DEST.  */
    while (EDGE_COUNT (bb->preds) > 0)


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