Re: [PATCH] lower-bitint: Remove single label _BitInt switches [PR113737]

[Richard Biener <rguenther@suse.de>]

On Mon, 5 Feb 2024, Jakub Jelinek wrote:

> Hi!
> 
> The following testcase ICEs, because group_case_labels_stmt optimizes
>   switch (a.0_7) <default: <L6> [50.00%], case 0: <L7> [50.00%], case 2: <L7> [50.00%]>
> where L7 block starts with __builtin_unreachable (); to
>   switch (a.0_7) <default: <L6> [50.00%]>
> and single label GIMPLE_SWITCH is something the switch expansion refuses to
> lower:
>   if (gimple_switch_num_labels (m_switch) == 1
>       || range_check_type (index_type) == NULL_TREE)
>     return false;
> (range_check_type never returns NULL for BITINT_TYPE), but the gimple
> lowering pass relies on all large/huge _BitInt switches to be lowered
> by that pass.
> 
> The following patch just removes those after making the single successor
> edge EDGE_FALLTHRU.  I've done it even if !optimize just in case in case
> we'd end up with single case label from earlier passes.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

Richard.

> 2024-02-05  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR tree-optimization/113737
> 	* gimple-lower-bitint.cc (gimple_lower_bitint): If GIMPLE_SWITCH
> 	has just a single label, remove it and make single successor edge
> 	EDGE_FALLTHRU.
> 
> 	* gcc.dg/bitint-84.c: New test.
> 
> --- gcc/gimple-lower-bitint.cc.jj	2024-02-02 11:30:05.801776658 +0100
> +++ gcc/gimple-lower-bitint.cc	2024-02-03 12:49:52.997777574 +0100
> @@ -5832,7 +5832,14 @@ gimple_lower_bitint (void)
>  
>  	  if (optimize)
>  	    group_case_labels_stmt (swtch);
> -	  switch_statements.safe_push (swtch);
> +	  if (gimple_switch_num_labels (swtch) == 1)
> +	    {
> +	      single_succ_edge (bb)->flags |= EDGE_FALLTHRU;
> +	      gimple_stmt_iterator gsi = gsi_for_stmt (swtch);
> +	      gsi_remove (&gsi, true);
> +	    }
> +	  else
> +	    switch_statements.safe_push (swtch);
>  	}
>      }
>  
> --- gcc/testsuite/gcc.dg/bitint-84.c.jj	2024-02-03 12:56:08.153622744 +0100
> +++ gcc/testsuite/gcc.dg/bitint-84.c	2024-02-03 12:57:05.425835789 +0100
> @@ -0,0 +1,32 @@
> +/* PR tree-optimization/113737 */
> +/* { dg-do compile { target bitint } } */
> +/* { dg-options "-O2 -std=c23" } */
> +
> +#if __BITINT_MAXWIDTH__ >= 129
> +_BitInt(129) a;
> +#else
> +_BitInt(63) a;
> +#endif
> +
> +int b[1], c;
> +
> +int
> +foo (void)
> +{
> +  switch (a)
> +  case 0:
> +  case 2:
> +    return 1;
> +  return 0;
> +}
> +
> +void
> +bar (int i)
> +{
> +  for (;; ++i)
> +    {
> +      c = b[i];
> +      if (!foo ())
> +	__asm__ ("");
> +    }
> +}
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)