[clang] Define ptrauth_sign_constant builtin. (#93904)

This is a constant-expression equivalent to
ptrauth_sign_unauthenticated.  Its constant nature lets us guarantee
a non-attackable sequence is generated, unlike
ptrauth_sign_unauthenticated which we generally discourage using.

It being a constant also allows its usage in global initializers, though
requiring constant pointers and discriminators.

The value must be a constant expression of pointer type which evaluates
to a non-null pointer.

The key must be a constant expression of type ptrauth_key.
The extra data must be a constant expression of pointer or integer type;
if an integer, it will be coerced to ptrauth_extra_data_t.
The result will have the same type as the original value.

This can be used in constant expressions.

Co-authored-by: John McCall <rjmccall@apple.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 9b63f47..04e1a39 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -937,6 +937,11 @@ public:
   // Return the function body address of the given function.
   llvm::Constant *GetFunctionStart(const ValueDecl *Decl);
 
+  llvm::Constant *
+  getConstantSignedPointer(llvm::Constant *Pointer, unsigned Key,
+                           llvm::Constant *StorageAddress,
+                           llvm::ConstantInt *OtherDiscriminator);
+
   // Return whether RTTI information should be emitted for this target.
   bool shouldEmitRTTI(bool ForEH = false) {
     return (ForEH || getLangOpts().RTTI) && !getLangOpts().CUDAIsDevice &&