Re: BUG #18722: Processing arrays with plpgsql raises errors

I wrote:
> What EEOP_NULLIF needs to do is pass a read-only pointer to the
> equality function, so that the object is not modified and remains
> available to return if we want to do so.

> Attached is a quick WIP patch to handle that. It is missing a test
> case, but the real omission is that llvm_compile_expr()'s EEOP_NULLIF
> handling also needs to be fixed, and I'm pretty unsure how to do that.

Here's a fleshed-out patch with a test case and JIT support. This
is about the first time I've messed with LLVM, so I wouldn't mind
some review of what I did in llvmjit_expr.c. In particular, do I
correctly understand that "l_funcvalue(b, v_fcinfo, 0)" produces
a reference to a copy of the initial value of args[0].value?
It seems to work in testing --- the original R/W pointer is returned
out of the expression --- but if we returned the R/O pointer instead
it'd be mighty difficult to detect the resulting inefficiency.

> I'm wondering now if any of our other conditional expressions have
> similar bugs ...

I was amused to discover that case.sql already had infrastructure
suitable for testing this, thanks to bug #14472.

regards, tom lane