PR optimization/15242

	* params.def (PARAM_MAX_GOTO_DUPLICATION_INSNS): New param.
	* basic-block.h (duplicate_computed_gotos): Add prototype.
	* bb-reorder.c (duplicate_computed_gotos): New function to
	duplicate sufficiently small blocks ending in a computed jump.
	* passes.c (rest_of_compilation): Call duplicate_computed_gotos
	if not optimizing for size.
	* cfgcleanup.c (try_crossjump_bb): If not optimizing for size,
	never do tail merging for blocks ending in a computed jump.
	* doc/invoke.texi: Document the max-goto-duplication-insns param.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@94531 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 100 insertions, 2 deletions

diff --git a/gcc/bb-reorder.c b/gcc/bb-reorder.c
index cac7768c981..f454ce0a3c3 100644
--- a/gcc/bb-reorder.c
+++ b/gcc/bb-reorder.c
@@ -81,6 +81,7 @@
 #include "tm_p.h"
 #include "obstack.h"
 #include "expr.h"
+#include "params.h"
 
 /* The number of rounds.  In most cases there will only be 4 rounds, but
    when partitioning hot and cold basic blocks into separate sections of
@@ -1189,8 +1190,7 @@ copy_bb_p (basic_block bb, int code_may_grow)
   if (code_may_grow && maybe_hot_bb_p (bb))
     max_size *= 8;
 
-  for (insn = BB_HEAD (bb); insn != NEXT_INSN (BB_END (bb));
-       insn = NEXT_INSN (insn))
+  FOR_BB_INSNS (bb, insn)
     {
       if (INSN_P (insn))
 	size += get_attr_length (insn);
@@ -1985,6 +1985,104 @@ reorder_basic_blocks (unsigned int flags)
   timevar_pop (TV_REORDER_BLOCKS);
 }
 
+/* Duplicate the blocks containing computed gotos.  This basically unfactors
+   computed gotos that were factored early on in the compilation process to
+   speed up edge based data flow.  We used to not unfactoring them again,
+   which can seriously pessimize code with many computed jumps in the source
+   code, such as interpreters.  See e.g. PR15242.  */
+
+void
+duplicate_computed_gotos (void)
+{
+  basic_block bb, new_bb;
+  bitmap candidates;
+  int max_size;
+
+  if (n_basic_blocks <= 1)
+    return;
+
+  if (targetm.cannot_modify_jumps_p ())
+    return;
+
+  timevar_push (TV_REORDER_BLOCKS);
+
+  cfg_layout_initialize (0);
+
+  /* We are estimating the length of uncond jump insn only once
+     since the code for getting the insn length always returns
+     the minimal length now.  */
+  if (uncond_jump_length == 0)
+    uncond_jump_length = get_uncond_jump_length ();
+
+  max_size = uncond_jump_length * PARAM_VALUE (PARAM_MAX_GOTO_DUPLICATION_INSNS);
+  candidates = BITMAP_XMALLOC ();
+
+  /* Build the reorder chain for the original order of blocks.
+     Look for a computed jump while we are at it.  */
+  FOR_EACH_BB (bb)
+    {
+      if (bb->next_bb != EXIT_BLOCK_PTR)
+	bb->rbi->next = bb->next_bb;
+
+      /* If the block ends in a computed jump and it is small enough,
+	 make it a candidate for duplication.  */
+      if (computed_jump_p (BB_END (bb)))
+	{
+	  rtx insn;
+	  int size = 0;
+
+	  FOR_BB_INSNS (bb, insn)
+	    {
+	      if (INSN_P (insn))
+	        size += get_attr_length (insn);
+	      if (size > max_size)
+		break;
+	    }
+
+	  if (size <= max_size)
+	    bitmap_set_bit (candidates, bb->index);
+	}
+    }
+
+  /* Nothing to do if there is no computed jump here.  */
+  if (bitmap_empty_p (candidates))
+    goto done;
+
+  /* Duplicate computed gotos.  */
+  FOR_EACH_BB (bb)
+    {
+      if (bb->rbi->visited)
+	continue;
+
+      bb->rbi->visited = 1;
+
+      /* BB must have one outgoing edge.  That edge must not lead to
+         the exit block or the next block.
+	 The destination must have more than one predecessor.  */
+      if (EDGE_COUNT(bb->succs) != 1
+	  || EDGE_SUCC(bb,0)->dest == EXIT_BLOCK_PTR
+	  || EDGE_SUCC(bb,0)->dest == bb->next_bb
+	  || EDGE_COUNT(EDGE_SUCC(bb,0)->dest->preds) <= 1)
+	continue;
+
+      /* The successor block has to be a duplication candidate.  */
+      if (!bitmap_bit_p (candidates, EDGE_SUCC(bb,0)->dest->index))
+	continue;
+
+      new_bb = duplicate_block (EDGE_SUCC(bb,0)->dest, EDGE_SUCC(bb,0));
+      new_bb->rbi->next = bb->rbi->next;
+      bb->rbi->next = new_bb;
+      new_bb->rbi->visited = 1;
+    }
+
+done:
+  cfg_layout_finalize ();
+
+  BITMAP_XFREE (candidates);
+
+  timevar_pop (TV_REORDER_BLOCKS);
+}
+
 /* This function is the main 'entrance' for the optimization that
    partitions hot and cold basic blocks into separate sections of the
    .o file (to improve performance and cache locality).  Ideally it