[cfe-commits] r166188 - /cfe/trunk/lib/Sema/SemaInit.cpp

Robert Muth robertm at google.com
Thu Oct 18 14:59:53 PDT 2012

On Thu, Oct 18, 2012 at 4:48 PM, David Blaikie <dblaikie at gmail.com> wrote:
> On Thu, Oct 18, 2012 at 1:45 PM, Douglas Gregor <dgregor at apple.com> wrote:
>> On Oct 18, 2012, at 9:57 AM, David Blaikie <dblaikie at gmail.com> wrote:
>>> Author: dblaikie
>>> Date: Thu Oct 18 11:57:32 2012
>>> New Revision: 166188
>>> URL: http://llvm.org/viewvc/llvm-project?rev=166188&view=rev
>>> Log:
>>> PR14021: Copy lookup results to ensure safe iteration.
>>> Within the body of the loop the underlying map may be modified via
>>>  Sema::AddOverloadCandidate
>>>    -> Sema::CompareReferenceRelationship
>>>    -> Sema::RequireCompleteType
>>> to avoid the use of invalid iterators the sequence is copied first.
>> Did you audit other uses of LookupConstructors to ensure that this is the only ticking time bomb in this area?
> [+Robert Muth]
> I've not performed any such audit, no. With the hack debug check
> inserted we could just run the whole test suite to see if anything
> pops up.

I did not  perform any such audit either. I feel those are only of limited use
and the time would be better spend addressing the root of the issue.
If there is interest I could  try add some diagnostic code to the DenseMap
which would only be enabled in Debug mode.
We kicked around some ideas over lunch and here was one suggestion
that could work:
add an atomic timestamp to each DenseMap.
increment the time step whenever iterators are invalidated (e.g. insertions),
Each iterator also holds a copy of the timestamp form when it was created
so we can compare it against the parent container timestamp when\ever
the iterator is used.
I have not thought this through all this much, so it may not work in the end.
Any feedback would be welcome.

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