flx marked an inline comment as done.
flx added inline comments.
================
Comment at:
clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp:98-101
auto Matches =
match(findAll(declStmt(has(varDecl(equalsNode(&InitializingVar))))
.bind("declStmt")),
+ Body, Context);
----------------
ymandel wrote:
> flx wrote:
> > ymandel wrote:
> > > Consider inspecting the `DeclContext`s instead, which should be much more
> > > efficient than searching the entire block. Pass the `FunctionDecl` as an
> > > argument instead of `Body`, since it is a `DeclContext`. e.g. `const
> > > DeclContext &Fun`
> > >
> > > Then, either
> > > 1. Call `Fun.containsDecl(InitializingVar)`, or
> > > 2. Search through the contexts yourself; something like:
> > > ```
> > > DeclContext* DC = InitializingVar->getDeclContext();
> > > while (DC != nullptr && DC != &Fun)
> > > DC = DC->getLexicalParent();
> > > if (DC == nullptr)
> > > // The reference or pointer is not initialized anywhere witin the
> > > function. We
> > > // assume its pointee is not modified then.
> > > return true;
> > > ```
> > Are #1 and #2 equivalent? From the implementation and comment I cannot tell
> > whether #1 would cover cases where the variable is not declared directly in
> > the function, but in child block:
> >
> > ```
> > void Fun() {
> > {
> > var i;
> > {
> > i.usedHere();
> > }
> > }
> > }
> > ```
> >
> > I'm also reading this as an optimization to more quickly determine whether
> > we can stop here. We still need to find the matches for the next steps, but
> > I think I could then limit matching to the DeclContext I found here. Is
> > this correct? For this I would actually need the DeclContext result from #2.
> A. I think you're right that #2 is more suited to what you need. I wasn't
> sure, so included both. Agreed that the comments are ambiguous.
> B. yes, this is just an optimization. it may be premature for that matter;
> just that match can be expensive and this seemed a more direct expression of
> the algorithm.
I was not able to pass the (possibly more narrow) DeclContext to the match
function as scope since match does not support DeclContexts.
I implemented isDeclaredInFunction() which iterates through the decl contexts
as you suggested. I'm not sure though whether we should start with
VarDecl::getDeclContext() or VarDecl::getLexicalDeclContext()?
While looking at VarDecl::getLexicalDeclContext() I discovered is VarDecl has
the following method:
```
/// Returns true for local variable declarations other than parameters.
/// Note that this includes static variables inside of functions. It also
/// includes variables inside blocks.
///
/// void foo() { int x; static int y; extern int z; }
bool isLocalVarDecl() const;
```
I think this is exactly what we'd want here. What do you think?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D103021/new/
https://reviews.llvm.org/D103021
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