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

This defines a new kind of IR Constant that represents a ptrauth signed
pointer, as used in AArch64 PAuth.

It allows representing most kinds of signed pointer constants used thus
far in the llvm ptrauth implementations, notably those used in the
Darwin and ELF ABIs being implemented for c/c++.  These signed pointer
constants are then lowered to ELF/MachO relocations.

These can be simply thought of as a constant `llvm.ptrauth.sign`, with
the interesting addition of discriminator computation: the `ptrauth`
constant can also represent a combined blend, when both address and
integer discriminator operands are used.  Both operands are otherwise
optional, with default values 0/null.

1 files changed, 24 insertions, 1 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 32b9a03..aee627b 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -517,7 +517,8 @@ public:
   static constexpr uint8_t NoCFIOpcode = 252;
   static constexpr uint8_t DSOLocalEquivalentOpcode = 251;
   static constexpr uint8_t BlockAddressOpcode = 250;
-  static constexpr uint8_t FirstSpecialOpcode = BlockAddressOpcode;
+  static constexpr uint8_t ConstantPtrAuthOpcode = 249;
+  static constexpr uint8_t FirstSpecialOpcode = ConstantPtrAuthOpcode;
 
   // Separate struct to make passing different number of parameters to
   // BitcodeConstant::create() more convenient.
@@ -1562,6 +1563,18 @@ Expected<Value *> BitcodeReader::materializeValue(unsigned StartValID,
         C = ConstantExpr::get(BC->Opcode, ConstOps[0], ConstOps[1], BC->Flags);
       } else {
         switch (BC->Opcode) {
+        case BitcodeConstant::ConstantPtrAuthOpcode: {
+          auto *Key = dyn_cast<ConstantInt>(ConstOps[1]);
+          if (!Key)
+            return error("ptrauth key operand must be ConstantInt");
+
+          auto *Disc = dyn_cast<ConstantInt>(ConstOps[2]);
+          if (!Disc)
+            return error("ptrauth disc operand must be ConstantInt");
+
+          C = ConstantPtrAuth::get(ConstOps[0], Key, Disc, ConstOps[3]);
+          break;
+        }
         case BitcodeConstant::NoCFIOpcode: {
           auto *GV = dyn_cast<GlobalValue>(ConstOps[0]);
           if (!GV)
@@ -3644,6 +3657,16 @@ Error BitcodeReader::parseConstants() {
                                   Record[1]);
       break;
     }
+    case bitc::CST_CODE_PTRAUTH: {
+      if (Record.size() < 4)
+        return error("Invalid ptrauth record");
+      // Ptr, Key, Disc, AddrDisc
+      V = BitcodeConstant::create(Alloc, CurTy,
+                                  BitcodeConstant::ConstantPtrAuthOpcode,
+                                  {(unsigned)Record[0], (unsigned)Record[1],
+                                   (unsigned)Record[2], (unsigned)Record[3]});
+      break;
+    }
     }
 
     assert(V->getType() == getTypeByID(CurTyID) && "Incorrect result type ID");