[all-commits] [llvm/llvm-project] f3fbd2: [clang][dataflow] Strengthen pointer comparison. (...

[martinboehme via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f3fbd21fa4e25496725c22d987e4e47e4c39c8b0
      https://github.com/llvm/llvm-project/commit/f3fbd21fa4e25496725c22d987e4e47e4c39c8b0
  Author: martinboehme <mboehme at google.com>
  Date:   2024-05-07 (Tue, 07 May 2024)

  Changed paths:
    M clang/lib/Analysis/FlowSensitive/Transfer.cpp
    M clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

  Log Message:
  -----------
  [clang][dataflow] Strengthen pointer comparison. (#75170)

-  Instead of comparing the identity of the `PointerValue`s, compare the
   underlying `StorageLocation`s.

- If the `StorageLocation`s are the same, return a definite "true" as
the
result of the comparison. Before, if the `PointerValue`s were different,
we
would return an atom, even if the storage locations themselves were the
same.

- If the `StorageLocation`s are different, return an atom (as before).
Pointers
that have different storage locations may still alias, so we can't
return a
   definite "false" in this case.

The application-level gains from this are relatively modest. For the
Crubit
nullability check running on an internal codebase, this change reduces
the
number of functions on which the SAT solver times out from 223 to 221;
the
number of "pointer expression not modeled" errors reduces from 3815 to
3778.

Still, it seems that the gain in precision is generally worthwhile.

@Xazax-hun inspired me to think about this with his

[comments](https://github.com/llvm/llvm-project/pull/73860#pullrequestreview-1761484615)
on a different PR.



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