[Bug ada/32234] Default pointer initialization not occuring - due to the use of <>

["baldrick at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #7 from baldrick at gcc dot gnu dot org  2007-06-07 07:07 -------
> Valgrind is helful only if there is a crash (segmentation fault).

This is completely wrong.  Valgrind detects problems that *may*
cause a crash.  The fact that crashes occur rarely doesn't mean
there isn't something wrong.  I already explained that you can't
expect to get a segmentation fault on a small program.  So for a
testcase I either had to provide the large (300k/loc) original
program which showed the segmentation fault systematically,
or a small program which basically never shows a segmentation
fault.  i.e. testcases become less and less deterministic as you
make them smaller.  However there is a way to keep things
deterministic: run under a tool such as valgrind.  Valgrind detects
the same problem every time no matter how big or small the testcase.
This makes it feasible to submit a minimal testcase which captures
the essential problem, even though when run normally (i.e. not under
valgrind) it executes fine.  In fact you will never get a segmentation
fault with the testcase I submitted because it doesn't ever dereference
the uninitialized pointer - but that doesn't matter because valgrind
notices that it contains an uninitialized value when the "if" compares
it with null. i.e. the testcase is good enough for debugging the compiler
problem.

Let me say it again: when run on the small testcase valgrind shows
the presence of an uninitialized value that doesn't cause any problems
when the small testcase is run - it causes problems on the large
program from which this testcase was reduced.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32234