[LLVMdev] How doesn't llvm generate IR for logical negate operation

[zhi chen]

I see. My CPU is a general Core i7 Ivy bridge CPU.

On Fri, Apr 10, 2015 at 6:48 PM, Bruce Hoult <bruce at hoult.org> wrote:

> I suppose that depends on your CPU.  Do you even have a CPU that supports
> operations on <N x i1> as packed bits in vector registers?
>
>
> On Sat, Apr 11, 2015 at 12:43 PM, zhi chen <zchenhn at gmail.com> wrote:
>
>> Yes, but my point is that there would be some overhead to do cast the <N
>> x i1> vectortype to an integerNty. Is there any good way to check not all
>> of these N bits in the vectortype are 0s?
>>
>> On Fri, Apr 10, 2015 at 5:37 PM, Bruce Hoult <bruce at hoult.org> wrote:
>>
>>> Sure, if you actually just want an i1 saying whether or not at least one
>>> bit is set to 1, then comparing against 0 is the right thing.
>>>
>>> That should end up generating a unary TST instruction on ISAs that have
>>> one.
>>>
>>> On Sat, Apr 11, 2015 at 12:29 PM, zhi chen <zchenhn at gmail.com> wrote:
>>>
>>>> Thanks, Bruce. So, what is the easiest way to check if there is any bit
>>>> set to 1 in a <N x i1> vector type? I used bitcast instruction to cast it
>>>> into "iN" first and them compare iN to 0. Do you have a better way to do
>>>> it? Thanks again.
>>>>
>>>> On Fri, Apr 10, 2015 at 5:22 PM, Bruce Hoult <bruce at hoult.org> wrote:
>>>>
>>>>> LLVM doesn't have a "logical neg" (or "not") operator. That's a C
>>>>> thing. Do a compare against 0 to create an i1 result, then zero extend the
>>>>> i1 to the size of integer result you want.
>>>>>
>>>>>
>>>>> On Sat, Apr 11, 2015 at 12:07 PM, zhi chen <zchenhn at gmail.com> wrote:
>>>>>
>>>>>> How can I generate LLVM IR for both logical NEG (!)? For example, if
>>>>>> I have Int32Ty a,
>>>>>>
>>>>>> For the bitwise NEG(~):
>>>>>>
>>>>>> c = ~a ;
>>>>>>
>>>>>> I can use the following API from LLVM:
>>>>>>
>>>>>> BinaryOperator *neg = BinaryOperator::CreateNeg(nbits, "bitwiseNEG", insertBefore);
>>>>>>
>>>>>> How, if I want to generate logical NEG:
>>>>>>
>>>>>> c = !a;
>>>>>>
>>>>>> what should I do for this?
>>>>>>
>>>>>> Thanks
>>>>>>
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>>>>>>
>>>>>
>>>>
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>>>
>>
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