llvm dev - Apr 2015 - [LLVMdev] How doesn't llvm generate IR for logical negate operation

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
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
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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
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>>
>>
>
> --
> This message has been scanned for viruses and
> dangerous content by *MailScanner* <http://www.mailscanner.info/>,
and is
> believed to be clean.
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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
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>
>>>>
>>>
>>
>> --
>> This message has been scanned for viruses and
>> dangerous content by *MailScanner*
<http://www.mailscanner.info/>, and
>> is
>> believed to be clean.
>
>
>
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