[PATCH] D75285: Mark restrict pointer or reference to const as invariant

[Jeroen Dobbelaere via Phabricator via cfe-commits]

jeroen.dobbelaere added a comment.

I don't think that 'restrict' is a good match for this behavior. For c++, the alias_set proposal (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4150.pdf) would be a better match.
You would put the read access of *p in its own universe; or even better, something like

  struct X {
    int a;
    char [[alias_set(MyOwnUniverseForX_b)]]  b;
  };

Unfortunatly, there is no implementation yet.

Imho, adding a '__attribute__((invariant))' or something similar (immutable ? const_invariant ?) would be a better approach. (hmm, I like 'immutable')

  char test2(X *x) {
    const char __attribute__((immutable))  *p = (const char __attribute__((immutable))*)&(x->b);
    // for all i:  p[i] will never be modified.
    return *p;
  }

Extra precautions are probably needed to ensure that the initialization of x->b is separated from the usage of it.


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https://reviews.llvm.org/D75285