Using LLVM intrinsic functions inside `llvmcall`

General Usage Performance
6

I’m sorry, in your case I think you have to use the module level IR.
with declarations and a function definition

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 and
julia/llvmcall2.jl at master · JuliaLang/julia · GitHub