Re: [COMMITTED] [range-op-float] Implement MINUS_EXPR.

[Xi Ruoyao <xry111@xry111.site>]

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Hi Aldy,

This commit breaks the attached test case at -O2 on x86_64-linux-gnu and
loongarch64-linux-gnu :(.

The code is simplified from Glibc: the breakage causes two Glibc test
failures on loongarch64-linux-gnu.

Reverting the commit can fix the breakage.

On Wed, 2022-11-09 at 08:07 +0100, Aldy Hernandez via Gcc-patches wrote:
> Now that the generic parts of the binary operators have been
> abstracted, implementing MINUS_EXPR is a cinch.
> 
> The op[12]_range entries will be submitted as a follow-up.
> 
> gcc/ChangeLog:
> 
>         * range-op-float.cc (class foperator_minus): New.
>         (floating_op_table::floating_op_table): Add MINUS_EXPR entry.
> ---
>  gcc/range-op-float.cc | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
> index 7075c25442a..d52e971f84e 100644
> --- a/gcc/range-op-float.cc
> +++ b/gcc/range-op-float.cc
> @@ -1884,6 +1884,29 @@ class foperator_plus : public
> range_operator_float
>  } fop_plus;
>  
>  
> +class foperator_minus : public range_operator_float
> +{
> +  void rv_fold (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, bool
> &maybe_nan,
> +               tree type,
> +               const REAL_VALUE_TYPE &lh_lb,
> +               const REAL_VALUE_TYPE &lh_ub,
> +               const REAL_VALUE_TYPE &rh_lb,
> +               const REAL_VALUE_TYPE &rh_ub) const final override
> +  {
> +    frange_arithmetic (MINUS_EXPR, type, lb, lh_lb, rh_ub,
> dconstninf);
> +    frange_arithmetic (MINUS_EXPR, type, ub, lh_ub, rh_lb,
> dconstinf);
> +
> +    // [+INF] - [+INF] = NAN
> +    if (real_isinf (&lh_ub, false) && real_isinf (&rh_ub, false))
> +      maybe_nan = true;
> +    // [-INF] - [-INF] = NAN
> +    else if (real_isinf (&lh_lb, true) && real_isinf (&rh_lb, true))
> +      maybe_nan = true;
> +    else
> +      maybe_nan = false;
> +  }
> +} fop_minus;
> +
>  // Instantiate a range_op_table for floating point operations.
>  static floating_op_table global_floating_table;
>  
> @@ -1917,6 +1940,7 @@ floating_op_table::floating_op_table ()
>    set (ABS_EXPR, fop_abs);
>    set (NEGATE_EXPR, fop_negate);
>    set (PLUS_EXPR, fop_plus);
> +  set (MINUS_EXPR, fop_minus);
>  }
>  
>  // Return a pointer to the range_operator_float instance, if there is

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University

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__attribute__((noipa,noinline))
int t(double a, double b)
{
	double c = a - b;
	if (!__builtin_isfinite(c)) {
		if (__builtin_isnan(c)) {
			if (!__builtin_isnan(a) && !__builtin_isnan(b))
				return 1;
		} else if (__builtin_isfinite(a) && __builtin_isfinite(b))
			return 2;
	} else if (c == 0 && a != b)
		return 3;
	return 4;
}

int main()
{
	double a = __builtin_inf();
	if (t(a, a) != 1)
		__builtin_abort();
}