Re: [PATCH] lower-bitint: Punt .*_OVERFLOW optimization if cast from IMAGPART_EXPR appears before REALPART_EXPR [PR113119]

[Richard Biener <rguenther@suse.de>]

On Thu, 4 Jan 2024, Jakub Jelinek wrote:

> Hi!
> 
> _BitInt lowering for .{ADD,SUB,MUL}_OVERFLOW calls which have both
> REALPART_EXPR and IMAGPART_EXPR used and have a cast from the IMAGPART_EXPR
> to a boolean or normal integral type lowers them at the point of
> the REALPART_EXPR statement (which is especially needed if the lhs of
> the call is complex with large/huge _BitInt element type); we emit the
> stmt to set the lhs of the cast at the same spot as well.
> Normally, the lowering of __builtin_{add,sub,mul}_overflow arranges
> the REALPART_EXPR to come before IMAGPART_EXPR, followed by cast from that,
> but as the testcase shows, a redundant __builtin_*_overflow call and VN
> can reorder those and we then ICE because the def-stmt of the former cast
> from IMAGPART_EXPR may appear after its uses.
> We already check that all of REALPART_EXPR, IMAGPART_EXPR and the cast
> from the latter appear in the same bb as the .{ADD,SUB,MUL}_OVERFLOW call
> in the optimization, the following patch just extends it to make sure
> cast appears after REALPART_EXPR; if not, we punt on the optimization and
> expand it as a store of a complex _BitInt on the location of the ifn call.
> Only the testcase in the testsuite is changed by the patch, all other
> __builtin_*_overflow* calls in the bitint* tests (and there are quite a few)
> have REALPART_EXPR first.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

Richard.

> 2024-01-04  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR tree-optimization/113119
> 	* gimple-lower-bitint.cc (optimizable_arith_overflow): Punt if
> 	both REALPART_EXPR and cast from IMAGPART_EXPR appear, but cast
> 	is before REALPART_EXPR.
> 
> 	* gcc.dg/bitint-61.c: New test.
> 
> --- gcc/gimple-lower-bitint.cc.jj	2023-12-22 12:27:58.497437164 +0100
> +++ gcc/gimple-lower-bitint.cc	2023-12-23 10:44:05.586522553 +0100
> @@ -305,6 +305,7 @@ optimizable_arith_overflow (gimple *stmt
>    imm_use_iterator ui;
>    use_operand_p use_p;
>    int seen = 0;
> +  gimple *realpart = NULL, *cast = NULL;
>    FOR_EACH_IMM_USE_FAST (use_p, ui, lhs)
>      {
>        gimple *g = USE_STMT (use_p);
> @@ -317,6 +318,7 @@ optimizable_arith_overflow (gimple *stmt
>  	  if ((seen & 1) != 0)
>  	    return 0;
>  	  seen |= 1;
> +	  realpart = g;
>  	}
>        else if (gimple_assign_rhs_code (g) == IMAGPART_EXPR)
>  	{
> @@ -338,13 +340,35 @@ optimizable_arith_overflow (gimple *stmt
>  	  if (!INTEGRAL_TYPE_P (TREE_TYPE (lhs2))
>  	      || TREE_CODE (TREE_TYPE (lhs2)) == BITINT_TYPE)
>  	    return 0;
> +	  cast = use_stmt;
>  	}
>        else
>  	return 0;
>      }
>    if ((seen & 2) == 0)
>      return 0;
> -  return seen == 3 ? 2 : 1;
> +  if (seen == 3)
> +    {
> +      /* Punt if the cast stmt appears before realpart stmt, because
> +	 if both appear, the lowering wants to emit all the code
> +	 at the location of realpart stmt.  */
> +      gimple_stmt_iterator gsi = gsi_for_stmt (realpart);
> +      unsigned int cnt = 0;
> +      do
> +	{
> +	  gsi_prev_nondebug (&gsi);
> +	  if (gsi_end_p (gsi) || gsi_stmt (gsi) == cast)
> +	    return 0;
> +	  if (gsi_stmt (gsi) == stmt)
> +	    return 2;
> +	  /* If realpart is too far from stmt, punt as well.
> +	     Usually it will appear right after it.  */
> +	  if (++cnt == 32)
> +	    return 0;
> +	}
> +      while (1);
> +    }
> +  return 1;
>  }
>  
>  /* If STMT is some kind of comparison (GIMPLE_COND, comparison assignment)
> --- gcc/testsuite/gcc.dg/bitint-61.c.jj	2023-12-23 10:46:17.808658852 +0100
> +++ gcc/testsuite/gcc.dg/bitint-61.c	2023-12-23 10:46:02.482874865 +0100
> @@ -0,0 +1,17 @@
> +/* PR tree-optimization/113119 */
> +/* { dg-do compile { target bitint } } */
> +/* { dg-options "-std=c23 -O2" } */
> +
> +_BitInt(8) b;
> +_Bool c;
> +#if __BITINT_MAXWIDTH__ >= 8445
> +_BitInt(8445) a;
> +
> +void
> +foo (_BitInt(4058) d)
> +{
> +  c = __builtin_add_overflow (a, 0ULL, &d);
> +  __builtin_add_overflow (a, 0ULL, &d);
> +  b = d;
> +}
> +#endif
> 
> 	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)