Make Julia’s Error Codes Even Better Than Elm’s

Internals & Design
51

Does this really require compiler work? We already have @noinline which is sufficient for this as far as I’m aware:

my_sqrt(x::Real) = x >= 0.0 ? sqrt(x) : my_sqrt_error(x);

@noinline my_sqrt_error(x) = throw(DomainError("my_sqrt requires inputs greater than 0, you gave $x which is less than 0"));

julia> @benchmark my_sqrt(x) setup=(x= 100*rand())
BenchmarkTools.Trial: 10000 samples with 1000 evaluations.
 Range (min … max):  2.159 ns … 20.240 ns  ┊ GC (min … max): 0.00% … 0.00%
 Time  (median):     2.160 ns              ┊ GC (median):    0.00%
 Time  (mean ± σ):   2.168 ns ±  0.192 ns  ┊ GC (mean ± σ):  0.00% ± 0.00%

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  2.16 ns        Histogram: frequency by time        2.21 ns <

 Memory estimate: 0 bytes, allocs estimate: 0.

julia> @benchmark sqrt(x) setup=(x= 100*rand())
BenchmarkTools.Trial: 10000 samples with 1000 evaluations.
 Range (min … max):  2.159 ns … 11.370 ns  ┊ GC (min … max): 0.00% … 0.00%
 Time  (median):     2.160 ns              ┊ GC (median):    0.00%
 Time  (mean ± σ):   2.167 ns ±  0.107 ns  ┊ GC (mean ± σ):  0.00% ± 0.00%

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  2.16 ns      Histogram: log(frequency) by time     2.21 ns <

 Memory estimate: 0 bytes, allocs estimate: 0.

In fact, now that I look, it appears that whoever wrote the sqrt(::Float64) method in Base already knew and took advantage of this:

julia> @code_typed sqrt(1.0)
CodeInfo(
1 ─ %1 = Base.lt_float(x, 0.0)::Bool
└──      goto #3 if not %1
2 ─      invoke Base.Math.throw_complex_domainerror(:sqrt::Symbol, x::Float64)::Union{}
└──      unreachable
3 ─ %5 = Base.Math.sqrt_llvm(x)::Float64
└──      return %5
) => Float64
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