[llvm] [AArch64][PAC] Select auth+load into LDRAA/LDRAB/LDRA[pre]. (PR #123769)

[Anatoly Trosinenko via llvm-commits]

================
@@ -1671,6 +1673,163 @@ bool AArch64DAGToDAGISel::tryIndexedLoad(SDNode *N) {
   return true;
 }
 
+bool AArch64DAGToDAGISel::tryAuthLoad(SDNode *N) {
+  LoadSDNode *LD = cast<LoadSDNode>(N);
+  EVT VT = LD->getMemoryVT();
+  if (VT != MVT::i64)
+    return false;
+
+  assert(LD->getExtensionType() == ISD::NON_EXTLOAD && "invalid 64bit extload");
+
+  ISD::MemIndexedMode AM = LD->getAddressingMode();
+  if (AM != ISD::PRE_INC && AM != ISD::UNINDEXED)
+    return false;
+  bool IsPre = AM == ISD::PRE_INC;
+
+  SDValue Chain = LD->getChain();
+  SDValue Ptr = LD->getBasePtr();
+
+  SDValue Base = Ptr;
+
+  int64_t OffsetVal = 0;
+  if (IsPre) {
+    OffsetVal = cast<ConstantSDNode>(LD->getOffset())->getSExtValue();
+  } else if (CurDAG->isBaseWithConstantOffset(Base)) {
+    // We support both 'base' and 'base + constant offset' modes.
+    ConstantSDNode *RHS = dyn_cast<ConstantSDNode>(Base.getOperand(1));
+    if (!RHS)
+      return false;
+    OffsetVal = RHS->getSExtValue();
+    Base = Base.getOperand(0);
+  }
+
+  // The base must be of the form:
+  //   (int_ptrauth_auth <signedbase>, <key>, <disc>)
+  // with disc being either a constant int, or:
+  //   (int_ptrauth_blend <addrdisc>, <const int disc>)
----------------
atrosinenko wrote:

Is `disc` being an opaque register (such as a non-blended address discriminator) supported as well?

https://github.com/llvm/llvm-project/pull/123769