[llvm] [PAC][IR][AArch64] Add "ptrauth(...)" Constant to represent signed pointers. (PR #85738)

[Ahmed Bougacha via llvm-commits]

================
@@ -4044,6 +4044,60 @@ bool LLParser::parseValID(ValID &ID, PerFunctionState *PFS, Type *ExpectedTy) {
     ID.NoCFI = true;
     return false;
   }
+  case lltok::kw_ptrauth: {
+    // ValID ::= 'ptrauth' '(' ptr @foo ',' i32 <key>
+    //                         (',' i64 <disc> (',' ptr addrdisc)? )? ')'
+    Lex.Lex();
+
+    Constant *Ptr, *Key;
+    Constant *Disc = nullptr, *AddrDisc = nullptr;
+
+    if (parseToken(lltok::lparen,
+                   "expected '(' in constant ptrauth expression") ||
+        parseGlobalTypeAndValue(Ptr) ||
+        parseToken(lltok::comma,
+                   "expected comma in constant ptrauth expression") ||
+        parseGlobalTypeAndValue(Key))
+      return true;
+    // If present, parse the optional disc/addrdisc.
+    if (EatIfPresent(lltok::comma))
+      if (parseGlobalTypeAndValue(Disc) ||
+          (EatIfPresent(lltok::comma) && parseGlobalTypeAndValue(AddrDisc)))
+        return true;
+    if (parseToken(lltok::rparen,
+                   "expected ')' in constant ptrauth expression"))
+      return true;
+
+    if (!Ptr->getType()->isPointerTy())
+      return error(ID.Loc, "constant ptrauth base pointer must be a pointer");
+
+    auto *KeyC = dyn_cast<ConstantInt>(Key);
+    if (!KeyC || KeyC->getBitWidth() != 32)
+      return error(ID.Loc, "constant ptrauth key must be i32 constant");
+
+    ConstantInt *DiscC = nullptr;
+    if (Disc) {
+      DiscC = dyn_cast<ConstantInt>(Disc);
+      if (!DiscC || DiscC->getBitWidth() != 64)
+        return error(
+            ID.Loc,
+            "constant ptrauth integer discriminator must be i64 constant");
+    } else {
+      DiscC = ConstantInt::get(Type::getInt64Ty(Context), 0);
+    }
+
+    if (AddrDisc) {
+      if (!AddrDisc->getType()->isPointerTy())
+        return error(
+            ID.Loc, "constant ptrauth address discriminator must be a pointer");
+    } else {
+      AddrDisc = ConstantPointerNull::get(PointerType::get(Context, 0));
----------------
ahmedbougacha wrote:

No, the base pointer and the addr-disc pointer aren't really related, other than "addr-disc points to memory that's initialized with the full `ptrauth()` signed pointer."  So IMO it makes sense to leave the addr-disc as address space 0 by default, though the targets where we'd have real ptrauth implementations don't have very sophisticated usage of address-spaces, so it's probably not the end of the world to forbid them entirely for now.

https://github.com/llvm/llvm-project/pull/85738