On 6/30/20 8:47 AM, David Edelsohn via Gcc-patches wrote:
The unexpected warning is
gcc/testsuite/g++.dg/analyzer/pr94028.C:28:21: warning: use of
possibly-NULL '<unknown>' where non-null expected [CWE-690]
[-Wanalyzer-possible-null-argument]
This is the same location as one of the existing "leak" warnings.
I'm surprised that the Wnonull change triggers
a -Wanalyzer-possible-null-argument warning. There is no
-Wnonnull for the test case with or without -fanalyzer (and
with or without optimization) so that suggests the two are
independent of one another.
I'm also not sure I see a justification for a nonnull warning
in the test. The note printed after the warning says:
| | (5) possible return of NULL to ‘f’
from ‘j::operator new’
| | (6) argument 1 (‘<unknown>’) from (4)
could be NULL where non-null expected
|
/src/gcc/master/gcc/testsuite/g++.dg/analyzer/pr94028.C:19:3: note:
argument 1 of ‘j::j(B*, int)’ must be non-null
19 | j (B *, int)
| ^
but the first argument in j::j(B*, int) is not marked nonnull,
and it's not the this pointer (treating those as implicitly
nonnull was one of the changes introduced by my patch).
FWIW, I don't remember if I saw it when going through the test
results for my patch but if I did, it's possible that I assumed
it was unrelated because of the -Wanalyzer- option. Sorry if
this was the wrong call.
Martin
How would you like pr94028.C to be adjusted in the testsuite to
account for this?
Thanks, David
On Tue, Jun 30, 2020 at 10:18 AM David Malcolm <dmalc...@redhat.com> wrote:
On Tue, 2020-06-30 at 09:51 -0400, David Edelsohn wrote:
The changes to the non-null warning now produce an additional warning
for analyzer/pr94028.C on one of the "leak" lines. This causes new
failures on trunk.
Hi David
Do you have the output to hand? What is the full text of the new
diagnostic?
Some high level questions:
* Ought GCC to warn for that code? (or not)
* Is it behavior we ought to have a test for?
Note that AFAIK there are *two* kinds of non-null warnings that GCC can
emit: the kind emitted by Martin's code, versus those emitted by
-fanalyzer (the latter imply the much more expensive analysis performed
by -fanalyzer, and are controlled by the various -Wanalyzer-*null*
options; see
https://gcc.gnu.org/onlinedocs/gcc-10.1.0/gcc/Static-Analyzer-Options.html
)
Because non-null is not the purpose of the analyzer test, I propose
pruning the output to resolve the new failures.
Looking back through bugzilla, it seems that the main purpose of adding
that test was to ensure that -fanalyzer doesn't ICE on that code.
At some point I hope to properly support C++ in -fanalyzer, at which
point some kind of null warning may be warranted on that code. Sadly
I'm not yet at that point. FWIW I'm currently working on a big rewrite
of how state is tracked within the analyzer, as I've identified at
least two major flaws in the current implementation, which my rewrite
addresses. I'm deferring on C++ support until that rewrite is done.
Alternatively, I
could explicitly test for the additional non-null warning.
Do you have any preferences?
This test is controlled by analyzer.exp and thus, for example, is
disabled if the analyzer was disabled at configure time.
If this is coming from Martin's non-analyzer code, a third possibility
would be to use -Wno-something to disable that warning, so that the
analyzer test can focus on the -fanalyzer test, as it were (and if this
is a behavior that ought to be checked for in Martin's warning, then
copy the pertinent fragment of the testcase to one of the g++.dg cases,
I suppose). I think I prefer that approach.
How does this sound?
I propose appending
// { dg-prune-output "where non-null expected" }
to the file to prune the warning output.
Thanks, David
Thanks for looking into this; hope this is constructive.
Dave
