[clang] [clang] Implement function pointer type discrimination (PR #96992)

[Daniil Kovalev via cfe-commits]

================
@@ -3140,6 +3140,269 @@ ASTContext::getPointerAuthVTablePointerDiscriminator(const CXXRecordDecl *RD) {
   return llvm::getPointerAuthStableSipHash(Str);
 }
 
+/// Encode a function type for use in the discriminator of a function pointer
+/// type. We can't use the itanium scheme for this since C has quite permissive
+/// rules for type compatibility that we need to be compatible with.
+///
+/// Formally, this function associates every function pointer type T with an
+/// encoded string E(T). Let the equivalence relation T1 ~ T2 be defined as
+/// E(T1) == E(T2). E(T) is part of the ABI of values of type T. C type
+/// compatibility requires equivalent treatment under the ABI, so
+/// CCompatible(T1, T2) must imply E(T1) == E(T2), that is, CCompatible must be
+/// a subset of ~. Crucially, however, it must be a proper subset because
+/// CCompatible is not an equivalence relation: for example, int[] is compatible
+/// with both int[1] and int[2], but the latter are not compatible with each
+/// other. Therefore this encoding function must be careful to only distinguish
+/// types if there is no third type with which they are both required to be
+/// compatible.
+static void encodeTypeForFunctionPointerAuth(ASTContext &Ctx, raw_ostream &OS,
----------------
kovdan01 wrote:

This would be nice, thanks

https://github.com/llvm/llvm-project/pull/96992