[clang] [llvm] Add support for flag output operand "=@cc" for SystemZ. (PR #125970)

[Ulrich Weigand via cfe-commits]

================
@@ -1689,6 +1696,35 @@ Register SystemZTargetLowering::getExceptionSelectorRegister(
   return Subtarget.isTargetXPLINK64() ? SystemZ::R2D : SystemZ::R7D;
 }
 
+// Lower @cc targets via setcc.
+SDValue SystemZTargetLowering::LowerAsmOutputForConstraint(
+    SDValue &Chain, SDValue &Glue, const SDLoc &DL,
+    const AsmOperandInfo &OpInfo, SelectionDAG &DAG) const {
+  if (StringRef("{@cc}").compare(OpInfo.ConstraintCode) != 0)
+    return SDValue();
+
+  // Check that return type is valid.
+  if (OpInfo.ConstraintVT.isVector() || !OpInfo.ConstraintVT.isInteger() ||
+      OpInfo.ConstraintVT.getSizeInBits() < 8)
+    report_fatal_error("Glue output operand is of invalid type");
+
+  MachineFunction &MF = DAG.getMachineFunction();
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+  MRI.addLiveIn(SystemZ::CC);
+
+  if (Glue.getNode()) {
+    Glue = DAG.getCopyFromReg(Chain, DL, SystemZ::CC, MVT::i32, Glue);
+    Chain = Glue.getValue(1);
+  } else
+    Glue = DAG.getCopyFromReg(Chain, DL, SystemZ::CC, MVT::i32);
+
+  SDValue IPM = DAG.getNode(SystemZISD::IPM, DL, MVT::i32, Glue);
+  SDValue CC = DAG.getNode(ISD::SRL, DL, MVT::i32, IPM,
+                           DAG.getConstant(SystemZ::IPM_CC, DL, MVT::i32));
----------------
uweigand wrote:

I guess we should use `getCCResult` here.

https://github.com/llvm/llvm-project/pull/125970