# Using LLVM intrinsic functions inside \`llvmcall\`
**URL:** https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955
**Category:** Performance
**Tags:** llvm
**Created:** [September 28, 2022, 10:11pm UTC](https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955 "2022-09-28T22:11:29Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@matthias314](https://discourse.julialang.org/u/matthias314)
#### Post date: [September 28, 2022, 10:11pm UTC](https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955/1 "2022-09-28T22:11:29Z")
I’m playing around with `llvmcall`. I can use LLVM IR instructions (like [`add`](https://llvm.org/docs/LangRef.html#add-instruction)), but I cannot get intrinsic functions (like [`@llvm.abs.i32`](https://llvm.org/docs/LangRef.html#llvm-abs-intrinsic)) to work. From the post [Debugging float SIMD Intrinsics via llvmcall](https://discourse.julialang.org/t/debugging-float-simd-intrinsics-via-llvmcall/27855) I get the impression that it should possible. However, when I try to run the example discussed in that post, I get the error “Module IR does not contain specified entry function”. (Have the arguments to `llvmcall` possibly changed since then?) Anyway, an example of calling an intrinsic function would be appreciated.
---
### Author:  [@gbaraldi](https://discourse.julialang.org/u/gbaraldi)
#### Post date: [September 28, 2022, 10:21pm UTC](https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955/2 "2022-09-28T22:21:06Z")
Did you declare the intrinsic before calling it? Like in the example?
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### Author:  [@matthias314](https://discourse.julialang.org/u/matthias314)
#### Post date: [September 28, 2022, 10:36pm UTC](https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955/3 "2022-09-28T22:36:59Z")
I think so. Following the [advice](https://discourse.julialang.org/t/debugging-float-simd-intrinsics-via-llvmcall/27855/4) about the input argument type, I wrote:
```julia
using SIMD
function rsqrt(f)
Base.llvmcall(("declare <4 x float> @llvm.x86.sse.rsqrt.ps(<4 x float>) nounwind readnone", "
%2 = call <4 x float> @llvm.x86.sse.rsqrt.ps(<4 x float> %0)
ret <4 x float> %2"), Vec{4, Float32}, Tuple{NTuple{4, VecElement{Float32}},},
(VecElement(f[1]),VecElement(f[2]),VecElement(f[3]),VecElement(f[4])))
end
```
Then I get
```julia
julia> rsqrt(Vec(Float32(1),Float32(1),Float32(1),Float32(1)))
ERROR: Module IR does not contain specified entry function
```
The [documentation](https://docs.julialang.org/en/v1/base/c/#Core.Intrinsics.llvmcall) of `llvmcall` says that if the first argument is a tuple, then its second member must be “a string representing the name of the entry-point function to call”. In the example, this doesn’t seem to be the case.
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### Author:  [@gbaraldi](https://discourse.julialang.org/u/gbaraldi)
#### Post date: [September 28, 2022, 10:42pm UTC](https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955/4 "2022-09-28T22:42:00Z")
I see the issue here, you are passing the IR via a tuple, that method requires a tuple with an LLVM IR module with defined functions and what function to call. The way you are using it, all the IR should be in the same string without a tuple.
---
### Author:  [@matthias314](https://discourse.julialang.org/u/matthias314)
#### Post date: [September 28, 2022, 10:47pm UTC](https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955/5 "2022-09-28T22:47:41Z")
Could you post a working example? I’ve already tried
```julia
@generated function f(x::Int64)
quote
Base.llvmcall(("""
declare i64 @llvm.abs.i64(i64, i1)
%x = call i64 @llvm.abs.64(i64 %0, i1 0)
ret i64 %x
"""), Int64, Tuple{Int64}, x)
end
end
```
but that gives
```julia
julia> f(1)
ERROR: Failed to parse LLVM assembly:
:3:1: error: expected instruction opcode
declare i64 @llvm.abs.i64(i64, i1)
^
```
---
### Author:  [@gbaraldi](https://discourse.julialang.org/u/gbaraldi)
#### Post date: [September 28, 2022, 11:00pm UTC](https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955/6 "2022-09-28T23:00:58Z")
I’m sorry, in your case I think you have to use the module level IR.
with declarations and a function definition
```julia
function foo(x)
Base.llvmcall(("""
declare i64 @llvm.abs.i64(i64, i1)
define i64 @entry(i64) {
%x = call i64 @llvm.abs.i64(i64 %0, i1 0)
ret i64 %x
}
""","entry"), Int64, Tuple{Int64}, x)
end
```
There are a bunch of examples in [julia/llvmcall.jl at master · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/blob/master/test/llvmcall.jl) and
[julia/llvmcall2.jl at master · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/blob/master/test/llvmcall2.jl)
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### Author:  [@matthias314](https://discourse.julialang.org/u/matthias314)
#### Post date: [September 28, 2022, 11:16pm UTC](https://discourse.julialang.org/t/using-llvm-intrinsic-functions-inside-llvmcall/87955/7 "2022-09-28T23:16:19Z")
Great! Thanks!