sql: `EXPLAIN ANALYZE (DEBUG)` has seemingly exponential behavior on some UDFs

[yuzefovich]

If we adjust the regression test from #162512 to execute the statement via EXPLAIN ANALYZE (DEBUG), we have seemingly exponential blow-up in latency and RAM usage when populating opt-vv.txt file

CREATE TABLE t161993 (
  id INT8 NOT NULL DEFAULT 0,
  k VARCHAR(50) NULL,
  CONSTRAINT t1_pkey PRIMARY KEY (id ASC)
);
CREATE TABLE u161993 (
  code VARCHAR(20) NOT NULL,
  name VARCHAR NULL,
  active BOOL NULL DEFAULT true,
  flag BOOL NULL DEFAULT false,
  CONSTRAINT u161993_pkey PRIMARY KEY (code ASC)
);
CREATE FUNCTION f161993(p_in JSONB, OUT p_out JSONB)
  RETURNS JSONB
  LANGUAGE plpgsql
  AS $$
  DECLARE
  v1 BOOL;
  v2 BOOL;
  v3 TIMESTAMP;
  v4 INT8;
  v5 JSONB;
  v6 JSONB;
  v7 JSONB;
  v8 VARCHAR;
  v9 BOOL;
  v10 VARCHAR;
  v11 VARCHAR;
  BEGIN
  v2 := true;
  v5 := p_in;
  v8 := COALESCE(btrim(v5->>'code'), '1')::VARCHAR;
  v10 := '';
  v11 := '';
  -- Block 1
  IF v2 = true THEN
    SELECT id FROM t161993 WHERE k = split_part(v10, '|', 5) INTO v4;
    v2 := true;
  END IF;
  -- Block 2
  IF v4 IN (11, 16, 89) THEN
    v1 := COALESCE(btrim((v5->>'flag')), 'false')::BOOL;
  END IF;
  -- Block 3
  IF v2 = true THEN
    v7 := '{}'::JSONB;
  END IF;
  -- Block 4
  IF v2 = true THEN
    v8 := CASE WHEN EXISTS (SELECT 1 FROM u161993 AS x WHERE (x.code = v8) AND (x.active = true)) THEN v8 ELSE '1' END;
  END IF;
  -- Block 5
  IF v2 = true THEN
    v6 := '{}'::JSONB;
  END IF;
  -- Block 6
  IF (v2 = true) AND (v9::BOOL = true) THEN
    SELECT COALESCE(flag, false) FROM u161993 WHERE name = split_part(v11, '|', 4) INTO v9;
  END IF;
  -- Block 7
  IF v2 = true THEN
    v7 := '{}'::JSONB;
  END IF;
  -- Block 8
  IF v2 = true THEN
    v8 := CASE WHEN EXISTS (SELECT 1 FROM u161993 AS x WHERE (x.code = v8) AND (x.active = true)) THEN v8 ELSE '1' END;
  END IF;
  -- Block 9
  IF v2 = true THEN
    v6 := '{}'::JSONB;
  END IF;
  -- Block 10
  IF v2 = true THEN
    v7 := '{}'::JSONB;
  END IF;
  -- Block 11
  IF v2 = true THEN
    v8 := CASE WHEN EXISTS (SELECT 1 FROM u161993 AS x WHERE (x.code = v8) AND (x.active = true)) THEN v8 ELSE '1' END;
  END IF;
  -- Block 12
  IF v2 = true THEN
    v6 := '{}'::JSONB;
  END IF;
  -- Block 13
  IF v2 = true THEN
    v7 := '{}'::JSONB;
  END IF;
  -- Block 14
  IF v2 = true THEN
    v8 := CASE WHEN EXISTS (SELECT 1 FROM u161993 AS x WHERE (x.code = v8) AND (x.active = true)) THEN v8 ELSE '1' END;
  END IF;
  -- Block 15
  IF v2 = true THEN
    v6 := '{}'::JSONB;
  END IF;
  -- Block 16
  IF v2 = true THEN
    v7 := '{}'::JSONB;
  END IF;
  -- Block 17
  IF v2 = true THEN
    v8 := CASE WHEN EXISTS (SELECT 1 FROM u161993 AS x WHERE (x.code = v8) AND (x.active = true)) THEN v8 ELSE '1' END;
  END IF;
  -- Block 18
  IF v2 = true THEN
    v6 := '{}'::JSONB;
  END IF;
  -- Block 19
  IF v2 = true THEN
    v7 := '{}'::JSONB;
  END IF;
  -- Block 20
  IF v2 = true THEN
    v8 := CASE WHEN EXISTS (SELECT 1 FROM u161993 AS x WHERE (x.code = v8) AND (x.active = true)) THEN v8 ELSE '1' END;
  END IF;
  -- Block 21
  IF v2 = true THEN
    v6 := '{}'::JSONB;
  END IF;
  -- Block 22
  IF v2 = true THEN
    v7 := '{}'::JSONB;
  END IF;
  -- Block 23
  IF v2 = true THEN
    v8 := CASE WHEN EXISTS (SELECT 1 FROM u161993 AS x WHERE (x.code = v8) AND (x.active = true)) THEN v8 ELSE '1' END;
  END IF;
  -- Block 24
  IF v2 = true THEN
    v6 := '{}'::JSONB;
  END IF;
  -- Block 25
  IF v2 = true THEN
    v3 := clock_timestamp();
    v7 := v7::JSONB || jsonb_build_object('key', split_part(v10, '|', 5));
    p_out := '{}'::JSONB;
  END IF;
  END;
$$;
EXPLAIN ANALYZE (DEBUG) SELECT f161993('{}');

Jira issue: CRDB-61718