Re: [PATCH] ree: Fix -fcompare-debug issues in combine_reaching_defs [PR108573]

[Richard Biener <rguenther@suse.de>]

On Wed, 1 Feb 2023, Jakub Jelinek wrote:

> Hi!
> 
> The PR78437 r7-4871 changes made combine_reaching_defs punt on
> WORD_REGISTER_OPERATIONS targets if a setter of smaller than word
> register has wider uses.  This unfortunately breaks -fcompare-debug,
> because if such a use appears only in DEBUG_INSN(s), while all other
> uses aren't wider than the setter, we can REE optimize it without -g
> and not with -g.
> 
> Such decisions shouldn't be based on debug instructions.  We could try
> to reset them or adjust in some other way after we decide to perform the
> change, but at least on the testcase which used to fail on riscv64-linux
> the
> (debug_insn 8 7 9 2 (var_location:HI s (minus:HI (subreg:HI (and:DI (reg:DI 10 a0 [160])
>                 (const_int 1 [0x1])) 0)
>         (subreg:HI (ashiftrt:DI (reg/v:DI 9 s1 [orig:151 l ] [151])
>                 (debug_expr:SI D#1)) 0))) "pr108573.c":12:5 -1
>      (nil))
> clearly doesn't care about the upper bits and I have hard time imaging how
> could one end up with DEBUG_INSN which actually cares about those upper
> bits.
> 
> So, the following patch just ignores uses on DEBUG_INSNs in this case,
> if we run into something where we'd need to do something further later on,
> let's deal with it when we have a testcase for it.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux (admittedly
> non-WORD_REGISTER_OPERATIONS targets) and tested using a cross to
> riscv64-linux on the testcase, ok for trunk?

OK.

Richard.

> 2023-02-01  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR debug/108573
> 	* ree.cc (combine_reaching_defs): Don't return false for paradoxical
> 	subregs in DEBUG_INSNs.
> 
> 	* gcc.dg/pr108573.c: New test.
> 
> --- gcc/ree.cc.jj	2023-02-01 10:19:22.833436546 +0100
> +++ gcc/ree.cc	2023-02-01 12:25:57.468252609 +0100
> @@ -875,7 +875,8 @@ combine_reaching_defs (ext_cand *cand, c
>  
>  	  for (df_link *use = uses; use; use = use->next)
>  	    if (paradoxical_subreg_p (GET_MODE (*DF_REF_LOC (use->ref)),
> -				      GET_MODE (SET_DEST (*dest_sub_rtx))))
> +				      GET_MODE (SET_DEST (*dest_sub_rtx)))
> +		&& !DEBUG_INSN_P (DF_REF_INSN (use->ref)))
>  	      return false;
>  	}
>  
> @@ -963,7 +964,8 @@ combine_reaching_defs (ext_cand *cand, c
>  	      rtx dest2 = SET_DEST (*dest_sub_rtx2);
>  	      for (use = uses; use; use = use->next)
>  		if (paradoxical_subreg_p (GET_MODE (*DF_REF_LOC (use->ref)),
> -					  GET_MODE (dest2)))
> +					  GET_MODE (dest2))
> +		    && !DEBUG_INSN_P (DF_REF_INSN (use->ref)))
>  		  break;
>  	      if (use)
>  		break;
> --- gcc/testsuite/gcc.dg/pr108573.c.jj	2023-02-01 12:15:20.476577340 +0100
> +++ gcc/testsuite/gcc.dg/pr108573.c	2023-02-01 12:15:03.044832520 +0100
> @@ -0,0 +1,18 @@
> +/* PR debug/108573 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fcompare-debug" } */
> +
> +unsigned g;
> +
> +int bar (void);
> +int baz (int);
> +
> +void
> +foo (unsigned short s, long l)
> +{
> +  unsigned u = bar ();
> +  s &= __builtin_add_overflow_p (0, u, 0);
> +  s %= g;
> +  s -= l >> s;
> +  baz (s);
> +}
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
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