[PATCH] D91037: [clang-tidy] Fix crash in bugprone-redundant-branch-condition on ExprWithCleanups

[Zinovy Nis via Phabricator via cfe-commits]

zinovy.nis added inline comments.


================
Comment at: clang-tools-extra/test/clang-tidy/checkers/bugprone-redundant-branch-condition.cpp:1092
+      // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: redundant condition 'isSet' [bugprone-redundant-branch-condition]
+      // CHECK-FIXES: {{isSet}}
+    }
----------------
aaron.ballman wrote:
> zinovy.nis wrote:
> > aaron.ballman wrote:
> > > zinovy.nis wrote:
> > > > aaron.ballman wrote:
> > > > > zinovy.nis wrote:
> > > > > > aaron.ballman wrote:
> > > > > > > There's not a whole lot of context for FileCheck to determine if it's been correctly applied or not (same below) -- for instance, won't this pass even if no changes are applied because FileCheck is still going to find `isSet` in the file?
> > > > > > Thanks. Fixed.
> > > > > Maybe it's just early in the morning for me, but... I was expecting the transformation to be:
> > > > > ```
> > > > > if (RetT::Test(isSet).Ok() && isSet) {
> > > > >   if (RetT::Test(isSet).Ok() && isSet) {
> > > > >   }
> > > > > }
> > > > > ```
> > > > > turns into
> > > > > ```
> > > > > if (RetT::Test(isSet).Ok() && isSet) {
> > > > > }
> > > > > ```
> > > > > Why does it remove the `&& isSet` instead? That seems like it's changing the logic here from `if (true && false)` to `if (true)`.
> > > > IMO it's correct.
> > > > `isSet` cannot change its value between `if`s while `RetT::Test(isSet).Ok()` can.
> > > > So we don't need to re-evaluate `isSet` and need to re-evaluate `RetT::Test(isSet).Ok()` only.
> > > > 
> > > > 
> > > > 
> > > > > That seems like it's changing the logic here from if (true && false) to if (true).
> > > > 
> > > > 
> > > > As I understand only the second `if` is transformed.
> > > Does this only trigger as a redundant branch condition if the definition of `RetT::Test()` is available? Because `Test()` takes a `bool&` so it sure seems like `isSet` could be modified between the branches if the definition isn't found because it's being passed as a non-const reference to `Test()`.
> > 1) 
> > > if the definition of RetT::Test() is available?
> > 
> > Removing the body from RetT::Test changes nothing.
> > 
> > 2) Turning `RetT Test(bool &_isSet)` -> `RetT Test(bool _isSet)` also changes nothing.
> > 
> > 
> > 
> > 
> Given the following four ways of declaring `Test()`:
> ```
> static RetT Test(bool &_isSet); // #1
> static RetT Test(bool _isSet); // #2
> static RetT Test(const bool &_isSet); // #3
> static RetT Test(bool &_isSet) { return 0; } // #4
> ```
> I would expect #2 and #3 to behave the same way -- the `isSet` argument could never be modified by calling `Test()` and so the second `Test(isSet) && isSet` is partially redundant and the second `if` statement can drop the ` && isSet`. (Without dropping the `Test(isSet)` because the call could still modify some global somewhere, etc.)
> 
> I would expect #1 to not modify the second `if` statement at all because there's no way of knowing whether `Test(isSet) && isSet` is the same between the first `if` statement and the second one (because the second call to `Test(isSet)` may modify `isSet` in a way the caller can observe).
> 
> Ideally, #4 would be a case where we could remove the entire second `if` statement because we can identify that not only does `isSet` not get modified despite being passed by non-const reference, we can see that the `Test()` function doesn't modify any state at all. However, this seems like it would require data flow analysis and so I think it makes sense to treat #4 the same as #1.
> 
> That said, I just realized the check isn't being very careful with reference parameters in the first place: https://godbolt.org/z/P1aP3W, so your changes aren't introducing a new problem, they just happened to highlight an existing issue.
Please look at https://reviews.llvm.org/D91495 - there's a fix for it.


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  https://reviews.llvm.org/D91037/new/

https://reviews.llvm.org/D91037