zhi chen
2015-Apr-11 00:29 UTC
[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 >> >> >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150410/8f0ce264/attachment.html>
Bruce Hoult
2015-Apr-11 00:37 UTC
[LLVMdev] How doesn't llvm generate IR for logical negate operation
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.-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150411/e5462f63/attachment.html>
zhi chen
2015-Apr-11 00:43 UTC
[LLVMdev] How doesn't llvm generate IR for logical negate operation
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. > > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150410/5aa6a7fe/attachment.html>
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