hokein added inline comments.
================
Comment at: clang-tidy/performance/InefficientVectorOperationCheck.cpp:53-54
+ PushBackCall)),
+ hasParent(compoundStmt(unless(has(ReserveCall)),
+ has(VectorVarDefStmt))))
+ .bind("for_loop"),
----------------
aaron.ballman wrote:
> hokein wrote:
> > aaron.ballman wrote:
> > > hokein wrote:
> > > > aaron.ballman wrote:
> > > > > I'm really not keen on this. It will catch trivial cases, so there is
> > > > > some utility, but this will quickly fall apart with anything past the
> > > > > trivial case.
> > > > The motivation of this check is to find code patterns like `for (int i
> > > > = 0; i < n; ++i) { v.push_back(i); }` and clean them in our codebase
> > > > (we have lots of similar cases).
> > > > [These](https://docs.google.com/document/d/1Bbc-6DlNs6zQujWD5-XOHWbfPJVMG7Z_T27Kv0WcFb4/edit?usp=sharing)
> > > > are all cases we want to support. Using `hasParent` is a simple and
> > > > sufficient way to do it IMO.
> > > I'm not convinced of the utility without implementing this in a more
> > > sensitive way. Have you run this across any large code bases and found
> > > that it catches issues?
> > Yeah, the check catches ~2800 cases (regexp shows ~17,000 total usages) in
> > our internal codebase. And all caught cases are what we are interested in.
> > It would catch more if we support for-range loops and iterator-based
> > for-loops.
> I wasn't worried about it not triggering often enough, I was worried about it
> triggering too often because of the lack of sensitivity. If you randomly
> sample some of those 2800 cases, do they reserve the space in a way that your
> check isn't catching?
Ok, I see your concern now, thanks for pointing it out.
I have read through these caught cases. The results look reasonable. Most cases
(> 95%) are what we expected, the code pattern is like `vector<T> v; for (...)
{ v.push_back(...); }` where the vector definition statement and for-loop
statement are consecutive. Another option is to make the check more strict
(only detects the consecutive code pattern).
https://reviews.llvm.org/D31757
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