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Message-ID: <f957dbf6f94cd553478baaa1ad6066b67c71c7a6.camel@xry111.site>
Subject: Re: Implement a build-in function with floating point exceptions.
From: Xi Ruoyao <xry111@xry111.site>
To: =?gb2312?Q?=B3=C2_=D0=A1=C1=FA?= <chenxl04200420@outlook.com>, 
	"gcc-patches@gcc.gnu.org"
	 <gcc-patches@gcc.gnu.org>
Cc: "i@xen0n.name" <i@xen0n.name>, "xuchenghua@loongson.cn"
	 <xuchenghua@loongson.cn>, "chenglulu@loongson.cn" <chenglulu@loongson.cn>
Date: Tue, 29 Nov 2022 22:19:45 +0800
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On Tue, 2022-11-29 at 09:52 +0000, =E9=99=88 =E5=B0=8F=E9=BE=99 wrote:
> +(define_insn "<float_pattern><mode>2"
> +  [(set (match_operand:ANYF 0 "register_operand" "=3Df")
> +	(unspec:ANYF[(match_operand:ANYF 1 "register_operand" "f")]
> +		FLOAT))]
> +      "TARGET_HARD_FLOAT&&(flag_fp_int_builtin_inexact ||
> !flag_trapping_math)"
> +    =20
> "ftint<float_submenmonic>.<wl>.<fmt>\t%0,%1\n\tffint.<fmt>.<wl>\t%0,%0

It's wrong.  For example, consider ceil(0x1.0p+100).  0x1.0p+100 cannot
be represented by any 64-bit integer, so ftintrp.l.d will raise an
overflow exception and provide "some value" as the output.  Then ffint
can't produce the correct result.

Nacked-by: Xi Ruoyao <xry111@xry111.site>

I'd suggest to add frint.{w,l}.{s,d}.{rm,rp,rz} etc. (BTW, also the
variants without raising inexact exceptions) into a future LoongArch ISA
version for this.

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University