diagnostics: tweak diagnostic_path::interprocedural_p [PR106626]

diagnostics: tweak diagnostic_path::interprocedural_p [PR106626]

The region-creation event at the start of...

<source>: In function 'int_arr_write_element_after_end_off_by_one':
<source>:14:11: warning: buffer overflow [CWE-787] [-Wanalyzer-out-of-bounds]
   14 |   arr[10] = x;
      |   ~~~~~~~~^~~
  event 1
    |
    |   10 | int32_t arr[10];
    |      |         ^~~
    |      |         |
    |      |         (1) capacity is 40 bytes
    |
    +--> 'int_arr_write_element_after_end_off_by_one': events 2-3
           |
           |   12 | void int_arr_write_element_after_end_off_by_one(int32_t x)
           |      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           |      |      |
           |      |      (2) entry to 'int_arr_write_element_after_end_off_by_one'
           |   13 | {
           |   14 |   arr[10] = x;  /* { dg-line line } */
           |      |   ~~~~~~~~~~~
           |      |           |
           |      |           (3) out-of-bounds write from byte 40 till byte 43 but 'arr' ends at byte 40
           |
<source>:14:11: note: write of 4 bytes to beyond the end of 'arr'
   14 |   arr[10] = x;
      |   ~~~~~~~~^~~
<source>:14:11: note: valid subscripts for 'arr' are '[0]' to '[9]'

...makes diagnostic_manager::finish_pruning consider the path to be
interprocedural, and so it doesn't prune the function entry event.

This patch tweaks diagnostic_path::interprocedural_p to ignore
leading events outside of any function, so that it considers the
path to be intraprocedural, and thus diagnostic_manager::finish_pruning
prunes the function entry event, leading to this simpler output:

<source>: In function 'int_arr_write_element_after_end_off_by_one':
<source>:14:11: warning: buffer overflow [CWE-787] [-Wanalyzer-out-of-bounds]
   14 |   arr[10] = x;
      |   ~~~~~~~~^~~
  event 1
    |
    |   10 | int32_t arr[10];
    |      |         ^~~
    |      |         |
    |      |         (1) capacity is 40 bytes
    |
    +--> 'int_arr_write_element_after_end_off_by_one': event 2
           |
           |   14 |   arr[10] = x;
           |      |   ~~~~~~~~^~~
           |      |           |
           |      |           (2) out-of-bounds write from byte 40 till byte 43 but 'arr' ends at byte 40
           |
<source>:14:11: note: write of 4 bytes to beyond the end of 'arr'
<source>:14:11: note: valid subscripts for 'arr' are '[0]' to '[9]'

gcc/ChangeLog:
	PR analyzer/106626
	* diagnostic-path.h
	(diagnostic_path::get_first_event_in_a_function): New decl.
	* diagnostic.cc (diagnostic_path::get_first_event_in_a_function):
	New.
	(diagnostic_path::interprocedural_p): Ignore leading events that
	are outside of any function.

gcc/testsuite/ChangeLog:
	PR analyzer/106626
	* gcc.dg/analyzer/out-of-bounds-multiline-1.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>