Profiler reports wrong or missing PSQL line statistics #9220

PLG$PROF_PSQL_STATS (and PLG$PROF_PSQL_STATS_VIEW) has wrong data for some common PSQL constructs:

1. FOR SELECT / FOR EXECUTE STATEMENT loops are counted wrong.
   The profiler only changes the current line when a statement starts. The next fetch of the loop
   does not start the FOR statement again, so:

   • the FOR line counts 1 (only the open), not one per fetch;
   • the time of each fetch is charged to the last line of the loop body;
   • when the body has only one statement, the current line never changes, so the body line also
     counts 1 instead of the number of iterations.

2. Some statements are not in the report at all.
   DSQL wraps some statements in internal BLR nodes, and the source line/column is attached to the
   wrapper instead of the statement:

   • DML, EXCEPTION, EXECUTE STATEMENT and MERGE in a block that has WHEN handlers;
   • UPDATE OR INSERT, always;
   • FOR EXECUTE STATEMENT, always.

   Those lines are missing from the stats, and their time is charged to the line before them.

Test case

create database 'profiler-test.fdb';

create table t (id integer);
insert into t select row_number() over () from rdb$types rows 5;
commit;

select rdb$profiler.start_session('test') from rdb$database;

set term !;

execute block as
    declare n integer = 0;
begin
    for select id from t into :n do
        n = n + 1;
end!

execute block as
    declare n integer = 0;
begin
    insert into t values (100);
    update or insert into t values (101) matching (id);
    for execute statement 'select id from t' into :n do
        n = n + 1;
    when any do
        n = 0;
end!

set term ;!

execute procedure rdb$profiler.finish_session(true);
commit;

select statement_id, line_num, column_num, counter
  from plg$profiler.plg$prof_psql_stats_view
  order by statement_id, line_num, column_num;

drop database;

Current result

First block (5 rows):

Second block (7 rows): lines 4 (insert), 5 (update or insert) and 6 (for execute statement) are
missing, and line 7 (n = n + 1) counts 1.

Expected result

First block:

Second block:

Fetch time should be charged to the FOR line, not to the loop body.

The missing lines can be fixed when the BLR is parsed, so routines already stored in a database
get correct stats without being recompiled.