[PATCH] D140860: [Diagnostics][NFC] Fix -Wlogical-op-parentheses warning inconsistency for const and constexpr values

[Takuya Shimizu via Phabricator via cfe-commits]

hazohelet added a comment.

As you point out, enhancement may be more accurate than bug fix.
There are rare cases where enabling a warning for missing parentheses in `constexpr` logical expressions can be helpful, I think. For example, consider the following code:

  constexpr A = ...;
  constexpr B = ...;
  constexpr C = ...;
  
  static_assert(!(A && B || C));

In this case, the static assertion will only be successful if `(A && B || C)` evaluates to `false`, which is equivalent to the following combinations of values for `A`, `B`, and `C`:

  (A, B, C) = (T, F, F) (F, T, F) (F, F, F)

Note that `T` means `true` and `F` means `false`. Here, `C` is always `false`, so `A && B || C` matches the case of `a && b || 0`. Thus, the warning is not issued before this patch.
If the programmer is not careful and assumes that `(A && B || C)` is equivalent to `(A && (B || C))`, then they expect the values of `A`, `B`, and `C` to also include the following combinations:

  (A, B, C) = (F, T, T) (F, F, T)

This would require the programmer to consider additional, unnecessary combinations after the successful static assertion.

Enabling a warning for missing parentheses in this scenario could help prevent the programmer from making this mistake.


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  https://reviews.llvm.org/D140860/new/

https://reviews.llvm.org/D140860