[-Wunsafe-buffer-usage] Add support for dependent values with deref

[patrykstefanski]

Before this change, we could only map ValueDecl to Expr to model dependent values. This change adds support for mapping ValueDecl with optional dereference to Expr. For example, this allows us to model dependent values with the following mapping:

  count -> 42
  *out_count -> 100

Supporting dereference is necessary in order to check assignments to inout pointer and count in the future.

[patrykstefanski]

This is taken from the original PR: #11490

[hnrklssn]

What happens with something like void foo(int * __counted_by(x) &p, int &x) in this model?

[patrykstefanski]

What happens with something like void foo(int * __counted_by(x) &p, int &x) in this model?

We don't have plans to support C++ refs. If any of this works, we should file a bug and fix it.

[ziqingluo-90]

The trySubstituteAndSimplify function only applies to Other in the comparator. Do you want to apply such substitution to both comparands?

[patrykstefanski]

I updated VisitUnaryOperator to try to substitute Self before comparing the expr with Other. So, if Self has deref, it will substitute it first, and then recursively compare to Other.

[ziqingluo-90]

What is a motivating example of this? I'm curious where you can extract the information that *out_count -> 100?

[patrykstefanski]

What is a motivating example of this? I'm curious where you can extract the information that *out_count -> 100?

A test case from my original PR:

void good_inout_subspan_const(int *__counted_by(*count) *p, size_t *count, std::span<int> sp) {
  *p = sp.first(42).data();
  *count = 42;
}

Here, we would have *count -> 42.

[patrykstefanski]

@swift-ci llvm test

[patrykstefanski]

@swift-ci test llvm