Re: [PATCH] bbpart: Fix up ICE on asm goto [PR108596]

[Richard Biener <rguenther@suse.de>]

On Tue, 31 Jan 2023, Jakub Jelinek wrote:

> Hi!
> 
> On the following testcase we have asm goto in hot block with 2 successors,
> one cold to which it both falls through and has one of the label
> pointing to it and another hot successor with another label.
> 
> Now, during bbpart we want to ensure that no blocks from one partition fall
> through into a block in a different partition.  fix_up_fall_thru_edges
> does that by temporarily clearing the EDGE_CROSSING on the fallthrough edge,
> calling force_nonfallthru and then depending on whether it created a new
> bb either set EDGE_CROSSING on the single successor edge from the new bb
> (the new bb is kept in the same partition as the predecessor block), or
> if no new bb has been created setting EDGE_CROSSING back on the fallthru
> edge which has been forced non-EDGE_FALLTHRU.
> For asm goto this doesn't always work, force_nonfallthru can create a new bb
> and change the fallthrough edge to point to that, but if the original
> fallthru destination block has its label referenced among the asm goto
> labels, it will create a new non-fallthru edge for the label(s).
> But because we've temporarily cheated and cleared EDGE_CROSSING on the edge,
> it is cleared on the new edge as well, then the caller sees we've created
> a new bb and just sets EDGE_CROSSING on the single fallthru edge from the
> new bb.  But the direct edge from cur_bb to fallthru edge's destination
> isn't handled and fails afterwards consistency checks, because it crosses
> partitions.
> 
> The following patch notes the case and sets EDGE_CROSSING on that edge too.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

Thanks,
Richard.

> 2023-01-31  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR rtl-optimization/108596
> 	* bb-reorder.cc (fix_up_fall_thru_edges): Handle the case where cur_bb
> 	ends with asm goto and has a crossing fallthrough edge to the same bb
> 	that contains at least one of its labels by restoring EDGE_CROSSING
> 	flag even on possible edge from cur_bb to new_bb successor.
> 
> 	* gcc.c-torture/compile/pr108596.c: New test.
> 
> --- gcc/bb-reorder.cc.jj	2023-01-02 09:32:39.000000000 +0100
> +++ gcc/bb-reorder.cc	2023-01-30 17:59:29.222096645 +0100
> @@ -1998,6 +1998,7 @@ fix_up_fall_thru_edges (void)
>  		     becomes EDGE_CROSSING.  */
>  
>  		  fall_thru->flags &= ~EDGE_CROSSING;
> +		  unsigned old_count = EDGE_COUNT (cur_bb->succs);
>  		  basic_block new_bb = force_nonfallthru (fall_thru);
>  
>  		  if (new_bb)
> @@ -2009,7 +2010,25 @@ fix_up_fall_thru_edges (void)
>  		      gcc_assert (BB_PARTITION (new_bb)
>                                    == BB_PARTITION (cur_bb));
>  
> -		      single_succ_edge (new_bb)->flags |= EDGE_CROSSING;
> +		      edge e = single_succ_edge (new_bb);
> +		      e->flags |= EDGE_CROSSING;
> +		      if (EDGE_COUNT (cur_bb->succs) > old_count)
> +			{
> +			  /* If asm goto has a crossing fallthrough edge
> +			     and at least one of the labels to the same bb,
> +			     force_nonfallthru can result in the fallthrough
> +			     edge being redirected and a new edge added for the
> +			     label or more labels to e->dest.  As we've
> +			     temporarily cleared EDGE_CROSSING flag on the
> +			     fallthrough edge, we need to restore it again.
> +			     See PR108596.  */
> +			  rtx_insn *j = BB_END (cur_bb);
> +			  gcc_checking_assert (JUMP_P (j)
> +					       && asm_noperands (PATTERN (j)));
> +			  edge e2 = find_edge (cur_bb, e->dest);
> +			  if (e2)
> +			    e2->flags |= EDGE_CROSSING;
> +			}
>  		    }
>  		  else
>  		    {
> --- gcc/testsuite/gcc.c-torture/compile/pr108596.c.jj	2023-01-30 18:01:02.252730008 +0100
> +++ gcc/testsuite/gcc.c-torture/compile/pr108596.c	2023-01-30 18:00:32.405168470 +0100
> @@ -0,0 +1,26 @@
> +/* PR rtl-optimization/108596 */
> +
> +__attribute__((__cold__)) void foo (void);
> +void bar (void);
> +
> +void
> +baz (void)
> +{
> +  asm goto ("" : : : : l1, l0);
> +  goto l0;
> +l1:
> +  bar ();
> +l0:
> +  foo ();
> +}
> +
> +void
> +qux (void)
> +{
> +  asm goto ("" : : : : l1, l0);
> +  __builtin_unreachable ();
> +l1:
> +  bar ();
> +l0:
> +  foo ();
> +}
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
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