Re: Special-case executor expression steps for common combinations

Hi,

On 2023-10-12 13:24:27 +0300, Heikki Linnakangas wrote:
> On 12/10/2023 12:48, Daniel Gustafsson wrote:
> > The attached patch adds special-case expression steps for common sets of steps
> > in the executor to shave a few cycles off during execution, and make the JIT
> > generated code simpler.
> >
> > * Adds EEOP_FUNCEXPR_STRICT_1 and EEOP_FUNCEXPR_STRICT_2 for function calls of
> > strict functions with 1 or 2 arguments (EEOP_FUNCEXPR_STRICT remains used for
> > > 2 arguments).
> > * Adds EEOP_AGG_STRICT_INPUT_CHECK_ARGS_1 which is a special case for the
> > common case of one arg aggs.
>
> Are these relevant when JITting? I'm a little sad if the JIT compiler cannot
> unroll these on its own. Is there something we could do to hint it, so that
> it could treat the number of arguments as a constant?

I think it's mainly important for interpreted execution.

> > skip extra setup for steps which are only interested in the side effects.
>
> I'm a little surprised if this makes a measurable performance difference,
> but sure, why not. It seems nice to be more explicit when you don't expect a
> return value.

IIRC this is more interesting for JIT than the above, because it allows LLVM
to know that the return value isn't needed and thus doesn't need to be
computed.

Greetings,

Andres Freund