Conditional iolist_to_binary?

[Dániel Szoboszlay]

Hi,

My guess the reason is that the iolist_to_binary(Value0) call compiles into
a call_ext, while the is_binary(Value0) to a test assembly instruction.
This means all live X registers have to be saved to the heap (and restored
later) in the first case. Inlining the is_binary check can save you that
(and a somewhat expensive external function call) when Value0 is already a
binary. But how much a difference this is depends on how many live X
registers you have at that point. Maybe try compiling the actual module
with erlc -S and compare the generated assembly code with and without the
if statement?

Cheers,
Daniel

On Fri, 27 Dec 2019 at 11:07, Loïc Hoguin <essen@REDACTED> wrote:

> Hello,
>
> I seem to be getting a small but noticeable performance improvement when
> I change the following:
>
> Value = iolist_to_binary(Value0)
>
> Into the following:
>
> Value = if
>      is_binary(Value0) -> Value0;
>      true -> iolist_to_binary(Value0)
> end
>
> At least when the input data is mostly binaries. Anyone else seeing this?
>
> The only difference between is_binary and iolist_to_binary seems to be
> that is_binary calls is_binary/binary_bitsize on the same if expression
> while iolist_to_binary has two if statements.
>
> What gives?
>
> Cheers,
>
> --
> Loïc Hoguin
> https://ninenines.eu
>
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