Re: [PATCH] internal-fn: Temporarily disable flag_trapv during .{ADD,SUB,MUL}_OVERFLOW etc. expansion [PR114753]

[Richard Biener <rguenther@suse.de>]

On Thu, 18 Apr 2024, Jakub Jelinek wrote:

> Hi!
> 
> __builtin_{add,sub,mul}_overflow{,_p} builtins are well defined
> for all inputs even for -ftrapv, and the -fsanitize=signed-integer-overflow
> ifns shouldn't abort in libgcc but emit the desired ubsan diagnostics
> or abort depending on -fsanitize* setting regardless of -ftrapv.
> The expansion of these internal functions uses expand_expr* in various
> places (e.g. MULT_EXPR at least in 2 spots), so temporarily disabling
> flag_trapv in all those spots would be hard.
> The following patch disables it around the bodies of 3 functions
> which can do the expand_expr calls.
> If it was in the C++ FE, I'd use some RAII sentinel, but I don't think
> we have one in the middle-end.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

Thanks,
Richard.

> 2024-04-18  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR middle-end/114753
> 	* internal-fn.cc (expand_mul_overflow): Save flag_trapv and
> 	temporarily clear it for the duration of the function, then
> 	restore previous value.
> 	(expand_vector_ubsan_overflow): Likewise.
> 	(expand_arith_overflow): Likewise.
> 
> 	* gcc.dg/pr114753.c: New test.
> 
> --- gcc/internal-fn.cc.jj	2024-03-23 08:22:50.490607002 +0100
> +++ gcc/internal-fn.cc	2024-04-17 13:44:21.673594413 +0200
> @@ -1631,7 +1631,11 @@ expand_mul_overflow (location_t loc, tre
>    rtx target = NULL_RTX;
>    signop sign;
>    enum insn_code icode;
> +  int save_flag_trapv = flag_trapv;
>  
> +  /* We don't want any __mulv?i3 etc. calls from the expansion of
> +     these internal functions, so disable -ftrapv temporarily.  */
> +  flag_trapv = 0;
>    done_label = gen_label_rtx ();
>    do_error = gen_label_rtx ();
>  
> @@ -2479,6 +2483,7 @@ expand_mul_overflow (location_t loc, tre
>        else
>  	expand_arith_overflow_result_store (lhs, target, mode, res);
>      }
> +  flag_trapv = save_flag_trapv;
>  }
>  
>  /* Expand UBSAN_CHECK_* internal function if it has vector operands.  */
> @@ -2499,7 +2504,11 @@ expand_vector_ubsan_overflow (location_t
>    rtx resvr = NULL_RTX;
>    unsigned HOST_WIDE_INT const_cnt = 0;
>    bool use_loop_p = (!cnt.is_constant (&const_cnt) || const_cnt > 4);
> +  int save_flag_trapv = flag_trapv;
>  
> +  /* We don't want any __mulv?i3 etc. calls from the expansion of
> +     these internal functions, so disable -ftrapv temporarily.  */
> +  flag_trapv = 0;
>    if (lhs)
>      {
>        optab op;
> @@ -2629,6 +2638,7 @@ expand_vector_ubsan_overflow (location_t
>      }
>    else if (resvr)
>      emit_move_insn (lhsr, resvr);
> +  flag_trapv = save_flag_trapv;
>  }
>  
>  /* Expand UBSAN_CHECK_ADD call STMT.  */
> @@ -2707,7 +2717,11 @@ expand_arith_overflow (enum tree_code co
>    prec0 = MIN (prec0, pr);
>    pr = get_min_precision (arg1, uns1_p ? UNSIGNED : SIGNED);
>    prec1 = MIN (prec1, pr);
> +  int save_flag_trapv = flag_trapv;
>  
> +  /* We don't want any __mulv?i3 etc. calls from the expansion of
> +     these internal functions, so disable -ftrapv temporarily.  */
> +  flag_trapv = 0;
>    /* If uns0_p && uns1_p, precop is minimum needed precision
>       of unsigned type to hold the exact result, otherwise
>       precop is minimum needed precision of signed type to
> @@ -2748,6 +2762,7 @@ expand_arith_overflow (enum tree_code co
>  	  ops.location = loc;
>  	  rtx tem = expand_expr_real_2 (&ops, NULL_RTX, mode, EXPAND_NORMAL);
>  	  expand_arith_overflow_result_store (lhs, target, mode, tem);
> +	  flag_trapv = save_flag_trapv;
>  	  return;
>  	}
>  
> @@ -2771,6 +2786,7 @@ expand_arith_overflow (enum tree_code co
>  	      if (integer_zerop (arg0) && !unsr_p)
>  		{
>  		  expand_neg_overflow (loc, lhs, arg1, false, NULL);
> +		  flag_trapv = save_flag_trapv;
>  		  return;
>  		}
>  	      /* FALLTHRU */
> @@ -2781,6 +2797,7 @@ expand_arith_overflow (enum tree_code co
>  	    case MULT_EXPR:
>  	      expand_mul_overflow (loc, lhs, arg0, arg1, unsr_p,
>  				   unsr_p, unsr_p, false, NULL);
> +	      flag_trapv = save_flag_trapv;
>  	      return;
>  	    default:
>  	      gcc_unreachable ();
> @@ -2826,6 +2843,7 @@ expand_arith_overflow (enum tree_code co
>  	  else
>  	    expand_mul_overflow (loc, lhs, arg0, arg1, unsr_p,
>  				 uns0_p, uns1_p, false, NULL);
> +	  flag_trapv = save_flag_trapv;
>  	  return;
>  	}
>  
> --- gcc/testsuite/gcc.dg/pr114753.c.jj	2024-04-17 13:55:16.246482369 +0200
> +++ gcc/testsuite/gcc.dg/pr114753.c	2024-04-17 13:54:14.035352376 +0200
> @@ -0,0 +1,14 @@
> +/* PR middle-end/114753 */
> +/* { dg-do run } */
> +/* { dg-options "-O2 -ftrapv" } */
> +
> +int
> +main ()
> +{
> +  volatile long long i = __LONG_LONG_MAX__;
> +  volatile long long j = 2;
> +  long long k;
> +  if (!__builtin_mul_overflow (i, j, &k) || k != -2LL)
> +    __builtin_abort ();
> +  return 0;
> +}
> 
> 	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)