Hi Linus,
On 17 March 2017 at 10:38, Dibyendu Majumdar <mobile@xxxxxxxxxxxxxxx> wrote:
> On 17 March 2017 at 00:24, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>> There's something seriously screwed up with explicit double casting.
>> See the differences between
>>
>> double f1(void) { return -1; }
>> double f2(void) { return (double)-1; }
>> double f3(void) { return -1.0; }
>>
>> and notice how the first one and third ones actually kind-of make
>> sense. The second one? Not so much, it just uses a 64-bit integer.
>>
>> The bug is already at the parse tree stage, the linearization doesn't
>> even see the cast.
>>
>> I think it's this, in simplify_cast():
>>
>> /* A cast of a constant? */
>> if (constant(src)) {
>> int sign = orig_type->ctype.modifiers & MOD_SIGNED;
>> long long val = get_cast_value(src->value, orig_size,
>> size, sign);
>> src = value_pseudo(val);
>> goto simplify;
>> }
>>
>> which doesn't even check whether it's a FP value, it just looks if
>> it's a constant and assumes it's an integer. At least it checks the
>> sign ;)
>>
>
> Thank you for pointing me to the location where the issue might be.
>
It seems that not only here but elsewhere also during simplification
of expressions involving constants there is no check whether the
instruction type is floating point. As a test I simply disabled the
simplification if the instruction type is floating point. Good news is
that while before the paranoia test was hanging and giving many
errors, but now it says:
No failures, defects nor flaws have been discovered.
Rounding appears to conform to the proposed IEEE standard P754.
The arithmetic diagnosed appears to be Excellent!
END OF TEST.
Regards
Dibyendu
--
To unsubscribe from this list: send the line "unsubscribe linux-sparse" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
