[PATCH] D156762: [-Wunsafe-buffer-usage][NFC] Refactor `getFixIts`---where fix-its are generated

[Artem Dergachev via Phabricator via cfe-commits]

NoQ added inline comments.


================
Comment at: clang/lib/Analysis/UnsafeBufferUsage.cpp:2219
+  // cannot be fixed...
+  eraseVarsForUnfixableGroupMates(FixItsForVariable, VarGrpMgr);
+  // Now `FixItsForVariable` gets further reduced: a variable is in
----------------
NoQ wrote:
> Architecturally speaking, I think I just realized something confusing about our code.
> 
> We already have variable groups well-defined at the Strategy phase, i.e. before we call `getFixIts()`, but then `getFixIts()` continues to reason about all variables collectively and indiscriminately. It continues to use entities such as the `FixItsForVariable` map which contain fixits for variables from *all* groups, not just the ones that are currently relevant. Then it re-introduces per-group data structures such as `ParmsNeedFixMask` on an ad-hoc basis, and it tries to compute them this way using the global, indiscriminate data structures.
> 
> I'm starting to suspect that the code would start making a lot more sense if we invoke `getFixIts()` separately for each variable group. So that each such invocation produced a single collective fixit for the group, or failed doing so.
> 
> This way we might be able to avoid sending steganographic messages through `FixItsForVariable`, but instead say directly "these are the variables that we're currently focusing on". It is the responsibility of the `Strategy` class to answer "should this variable be fixed?"; we shouldn't direct that question to any other data structures.
> 
> And if a group fails at any point, just early-return `None` and proceed directly to the next getFixIts() invocation for the next group. We don't need to separately record which individual variables have failed. In particular, `eraseVarsForUnfixableGroupMates()` would become a simple early return.
> 
> It probably also makes sense to store groups themselves inside the `Strategy` class. After all, fixing variables together is a form of strategy.
(I don't think this needs to be addressed in the current patch, but this could help us untangle the code in general.)


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https://reviews.llvm.org/D156762