================
@@ -185,10 +185,33 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type
*Ty) {
return getChar();
// Handle pointers and references.
----------------
rjmccall wrote:
Probably worth putting standard citations here:
```suggestion
// Handle pointers and references.
//
// C has a very strict rule for pointer aliasing. C23 6.7.6.1p2:
// For two pointer types to be compatible, both shall be identically
// qualified and both shall be pointers to compatible types.
//
// This rule is impractically strict; we want to at least ignore CVR
// qualifiers. Distinguishing by CVR qualifiers would make it UB to
// e.g. cast a `char **` to `const char * const *` and dereference it,
// which is too common and useful to invalidate. C++'s similar types
// rule permits qualifier differences in these nested positions; in fact,
// C++ even allows that cast as an implicit conversion.
//
// Other qualifiers could theoretically be distinguished, especially if
// they involve a significant representation difference. We don't
// currently do so, however.
//
// Computing the pointee type string recursively is implicitly more
// forgiving than the standards require. Effectively, we are turning
// the question "are these types compatible/similar" into "are
// accesses to these types allowed to alias". In both C and C++,
// the latter question has special carve-outs for signedness
// mismatches that only apply at the top level. As a result, we are
// allowing e.g. `int *` l-values to access `unsigned *` objects.
```
https://github.com/llvm/llvm-project/pull/76612
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