On 1/11/2022 3:40 PM, Jason Merrill wrote:
On 11/30/21 17:32, Martin Sebor via Gcc-patches wrote:
Attached is a revised patch with the following changes based
on your comments:
1) Set and use statement uids to determine which statement
precedes which in the same basic block.
2) Avoid testing flag_isolate_erroneous_paths_dereference.
3) Use post-dominance to decide whether to use the "maybe"
phrasing vs a definite form.
David raised (and in our offline discussion today reiterated)
an objection to the default setting of the option being
the strictest. I have not changed that in this revision.
See my rationale for this choice in my reply below:
https://gcc.gnu.org/pipermail/gcc-patches/2021-November/583176.html
In the latest C2x draft I see in the list of undefined behavior
"The value of a pointer that refers to space deallocated by a call to
the free or realloc function is used (7.22.3)."
So the case that would be technically undefined would be comparing the
reallocated pointer to the old pointer which has been deallocated.
The C++ draft is more nuanced: it says, "When the end of the duration
of a region of storage is reached, the values of all pointers
representing the address of any part of that region of storage become
invalid pointer values (6.8.3). Indirection through an invalid
pointer value and passing an invalid pointer value to a deallocation
function have undefined behavior. Any other use of an invalid pointer
value has implementation-defined behavior."
So the case above is implementation-defined in C++, not undefined.
Let's put =2 in -Wall for now.
With that change, this and the -Wdangling-pointer patch are OK on
Friday afternoon if there are no other comments before then.
THanks for picking this up. I've been busier than expected the last
several weeks.
jeff
