[llvm-dev] Beginner question: Calling intrinsic

[Craig Topper via llvm-dev]

If you are using x86, you probably need to pass something like
-mcpu=haswell or -mattr=bmi2 to enable support for the intrinsic. It seems
to -mcpu=native doesn't work for lli so it can't just autodetect your CPU.

~Craig

On Sun, Jan 7, 2018 at 7:54 AM, Nemanja Ivanovic via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi John,
> What targer are you trying to compile this for? I imagine this is just a
> case of using an X86 intrinsic on a non-X86 back end. Or is this an
> intrinsic you added and didn't provide a selection pattern for?
>
> In any case, this intrinsic makes it into the selection DAG and the
> instruction selector tries to select a sequence of instructions for it.
> However, it fails to find a pattern that it can match in your back end, so
> you get this error.
>
> As far as learning LLVM, The documentation at llvm.org is the best place
> to start. However, it is a huge project so you probably want to be a bit
> more specific in terms of what it is you want to learn. Based on your
> question, I imagine you want to learn how code generation works, so you
> might want to check out http://llvm.org/docs/CodeGenerator.html
>
> Hope this helps.
>
> On Sun, Jan 7, 2018 at 4:21 PM John Ky via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hello,
>>
>> I’m not sure if this is the right place to ask beginner questions.
>>
>> If not, please direct me to the appropriate place.
>>
>> I’m writing my first llvm program and I’m trying to call an intrinsic,
>> but failing.
>>
>> So far this is what I have:
>>
>> declare ccc i32 @llvm.x86.bmi.pdep.32(i32, i32)
>>
>> @.str2 = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
>>
>> declare i32 @printf(i8*, ...) nounwind
>>
>> ; Definition of main function
>> define i32 @main() {
>>   %res = call ccc i32 (i32, i32) @llvm.x86.bmi.pdep.32( i32 1, i32 1 )
>>
>>   %a = alloca i32, align 8
>>   %1 = load i32, i32* %a, align 8
>>   %ss = getelementptr inbounds [4 x i8], [4 x i8]*  @.str2, i32 0, i32 0
>>   call i32 (i8*, ...) @printf( i8* %ss, i32 %res)
>>
>>   ret i32 0
>> }
>>
>> When I run this code, I get the following error:
>>
>> $ lli helloWorld.ll
>> LLVM ERROR: Cannot select: intrinsic %llvm.x86.bmi.pdep.32
>>
>> Where am I going wrong?
>>
>> Also, what’s the best resource for learning llvm?
>>
>> Cheers,
>>
>> -John
>> ​
>>
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>>
>
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