Basic block numbers no longer in sequence

[Richard Earnshaw]

Sorry, I should have forwarded this to the list as well.

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To: law@cygnus.com
Cc: richard.earnshaw@arm.com
Cc: bernds@cygnus.co.uk
Reply-To: richard.earnshaw@arm.com
Organization: ARM Ltd.
Subject: Re: Basic block numbers no longer in sequence
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Date: Mon, 04 Oct 1999 11:45:46 +0100
From: Richard Earnshaw <rearnsha@arm.com>
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> OK.  We should have deleted block 4, not block 22.  ie, we need to
> delete the block we move since that will always be the one out of
> order.  And we need to reorder starting with the lower block number.
> Ugh.  I'll put this on my list (since it's my code breaking things)
> unless you want it. 


This has been causing a bootstrap failure for the ARM port, so I finally 
got around to looking at it over the weekend.  Here's a patch.  It isn't 
wonderfully clean, but the alternative is to rewrite (or duplicate the 
code in) merge_blocks_nomove to allow us to clean up the first basic block 
of the two listed.  I think doing the swap here instead is probably 
cleaner long term.

I've moved the rtl_dump message before the cleanup call so that it gets 
the block numbers correct without more hacking (though note that the 
numbers are the old numbers (before the re-order).

With this patch the arm-netbsd port will now bootstrap again.

Richard.

<date>  Richard Earnshaw (rearnsha@arm.com)

	* flow.c (merge_blocks_move_predecessor_nojumps): Re-order the basic
	block records so that merge_blocks_nomove will clean up correctly.



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Content-Type: application/x-patch ; name="bbdel.patch"
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Index: flow.c
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/flow.c,v
retrieving revision 1.161
diff -p -r1.161 flow.c
*** flow.c	1999/09/23 15:07:25	1.161
- --- flow.c	1999/10/04 10:38:26
*************** merge_blocks_move_predecessor_nojumps (a
*** 1946,1951 ****
- --- 1946,1952 ----
       basic_block a, b;
  {
    rtx start, end, insertpoint, barrier;
+   int index;
  
    start = a->head;
    end = a->end;
*************** merge_blocks_move_predecessor_nojumps (a
*** 1977,1990 ****
    /* Scramble the insn chain.  */
    reorder_insns (start, end, insertpoint);
  
- -   /* Now blocks A and B are contiguous.  Merge them.  */
- -   merge_blocks_nomove (a, b);
- - 
    if (rtl_dump_file)
      {
        fprintf (rtl_dump_file, "Moved block %d before %d and merged.\n",
  	       a->index, b->index);
      }
  
    return 1;
  }
- --- 1978,2000 ----
    /* Scramble the insn chain.  */
    reorder_insns (start, end, insertpoint);
  
    if (rtl_dump_file)
      {
        fprintf (rtl_dump_file, "Moved block %d before %d and merged.\n",
  	       a->index, b->index);
      }
+ 
+   /* Swap the records for the two blocks around.  Although we are 
deleting B,
+      A is now where B was and we want to compact the BB array from where
+      A used to be.  */
+   BASIC_BLOCK(a->index) = b;
+   BASIC_BLOCK(b->index) = a;
+   index = a->index;
+   a->index = b->index;
+   b->index = index;
+   
+   /* Now blocks A and B are contiguous.  Merge them.  */
+   merge_blocks_nomove (a, b);
  
    return 1;
  }

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