Re: JIT compiling expressions/deform + inlining prototype v2.0

On 01.09.2017 09:41, Andres Freund wrote:
> Hi,
>
> I previously had an early prototype of JITing [1] expression evaluation
> and tuple deforming. I've since then worked a lot on this.
>
> Here's an initial, not really pretty but functional, submission. This
> supports all types of expressions, and tuples, and allows, albeit with
> some drawbacks, inlining of builtin functions. Between the version at
> [1] and this I'd done some work in c++, because that allowed to
> experiment more with llvm, but I've now translated everything back.
> Some features I'd to re-implement due to limitations of C API.
>
>
> I've whacked this around quite heavily today, this likely has some new
> bugs, sorry for that :(

Can you please clarify the following fragment calculating attributes
alignment:

/* compute what following columns are aligned to */
+ if (att->attlen < 0)
+ {
+ /* can't guarantee any alignment after varlen field */
+ attcuralign = -1;
+ }
+ else if (att->attnotnull && attcuralign >= 0)
+ {
+ Assert(att->attlen > 0);
+ attcuralign += att->attlen;
+ }
+ else if (att->attnotnull)
+ {
+ /*
+ * After a NOT NULL fixed-width column, alignment is
+ * guaranteed to be the minimum of the forced alignment and
+ * length. XXX
+ */
+ attcuralign = alignto + att->attlen;
+ Assert(attcuralign > 0);
+ }
+ else
+ {
+ //elog(LOG, "attnotnullreset: %d", attnum);
+ attcuralign = -1;
+ }

I wonder why in this branch (att->attnotnull && attcuralign >= 0)
we are not adding "alignto" and comment in the following branch else if
(att->attnotnull)
seems to be not related to this branch, because in this case attcuralign
is expected to be less then zero wjhich means that previous attribute is
varlen field.

--
Konstantin Knizhnik
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