[clang-tools-extra] [llvm] [PowerPC] Implement llvm.set.rounding intrinsic (PR #67302)

[Serge Pavlov via cfe-commits]

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@@ -8900,6 +8900,83 @@ SDValue PPCTargetLowering::LowerINT_TO_FP(SDValue Op,
   return FP;
 }
 
+SDValue PPCTargetLowering::LowerSET_ROUNDING(SDValue Op,
+                                             SelectionDAG &DAG) const {
+  SDLoc Dl(Op);
+  MachineFunction &MF = DAG.getMachineFunction();
+  EVT PtrVT = getPointerTy(MF.getDataLayout());
+  SDValue Chain = Op.getOperand(0);
+
+  // If requested mode is constant, just use simpler mtfsb.
+  if (auto *CVal = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+    uint64_t Mode = CVal->getZExtValue();
+    if (Mode >= 4)
+      llvm_unreachable("Unsupported rounding mode!");
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spavloff wrote:

Would using `assert` be more appropriate?

https://github.com/llvm/llvm-project/pull/67302