Segher,
Does BCD comparison return false when either operand is invalid coding?
If yes, the result could be 3-way. We can check gt and eq bits for ge.
We still can't use crnot to only check lt bit as there could be invalid
coding.
Also, do you think finite-math-only excludes invalid coding? Seems GCC
doesn't clear define it.
Thanks.
Gui Haochen
On 2/6/2022 上午 6:05, Segher Boessenkool wrote:
> Hi!
>
> On Tue, May 31, 2022 at 06:56:00PM -0500, Segher Boessenkool wrote:
>> It's not clear to me how this can ever happen without finite_math_only?
>> The patch is safe, sure, but it may the real problem is elsewhere.
>
> So, it is incorrect the RTL for our bcd{add,sub} insns uses CCFP at all.
>
> CCFP stands for the result of a 4-way comparison, regular float
> comparison: lt gt eq un. But bcdadd does not have an unordered at all.
> Instead, it has the result of a 3-way comparison (lt gt eq), and bit 3
> is set if an overflow happened -- but still exactly one of bits 0..2 is
> set then! (If one of the inputs is an invalid number it sets bits 0..3
> to 0001 though.)
>
> So it would be much more correct and sensible to use regular integer
> comparison results here, so, CC.
>
> Does that fix the problem?
>
>
> Segher
