Re: Compiler warning in costsize.c

David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
> On 8 April 2017 at 04:42, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> BTW, is it really true that only these two places produce such warnings
>> on MSVC? I see about three dozen uses of PG_USED_FOR_ASSERTS_ONLY in our
>> tree, and I'd have expected all of those places to be causing warnings on
>> a compiler that doesn't have a way to understand that annotation.

> Seems that MSVC is happy once the variable is assigned, and does not
> bother checking if the variable is used after being assigned, whereas,
> some other compilers might see the variable as uselessly assigned.

> At the moment there are no other warnings from MSVC since all the
> other places the variable gets assigned a value in some code path.

I wonder if we shouldn't just do

RangeTblEntry *rte PG_USED_FOR_ASSERTS_ONLY;
ListCell *lc;

/* Should only be applied to base relations that are subqueries */
Assert(rel->relid > 0);
-#ifdef USE_ASSERT_CHECKING
rte = planner_rt_fetch(rel->relid, root);
Assert(rte->rtekind == RTE_SUBQUERY);
-#endif

and eat the "useless" calculation of rte.

regards, tom lane