[PowerPC] Implement llvm.set.rounding intrinsic (#67302)

Author: ecnelises

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -435,13 +435,13 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
   } else {
     setOperationAction(ISD::FMA  , MVT::f64, Legal);
     setOperationAction(ISD::FMA  , MVT::f32, Legal);
+    setOperationAction(ISD::GET_ROUNDING, MVT::i32, Custom);
+    setOperationAction(ISD::SET_ROUNDING, MVT::Other, Custom);
   }
 
   if (Subtarget.hasSPE())
     setLoadExtAction(ISD::EXTLOAD, MVT::f64, MVT::f32, Expand);
 
-  setOperationAction(ISD::GET_ROUNDING, MVT::i32, Custom);
-
   // If we're enabling GP optimizations, use hardware square root
   if (!Subtarget.hasFSQRT() &&
       !(TM.Options.UnsafeFPMath && Subtarget.hasFRSQRTE() &&
@@ -9060,6 +9060,103 @@ 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/mffscrni
+  if (auto *CVal = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+    uint64_t Mode = CVal->getZExtValue();
+    assert(Mode < 4 && "Unsupported rounding mode!");
+    unsigned InternalRnd = Mode ^ (~(Mode >> 1) & 1);
+    if (Subtarget.isISA3_0())
+      return SDValue(
+          DAG.getMachineNode(
+              PPC::MFFSCRNI, Dl, {MVT::f64, MVT::Other},
+              {DAG.getConstant(InternalRnd, Dl, MVT::i32, true), Chain}),
+          1);
+    SDNode *SetHi = DAG.getMachineNode(
+        (InternalRnd & 2) ? PPC::MTFSB1 : PPC::MTFSB0, Dl, MVT::Other,
+        {DAG.getConstant(30, Dl, MVT::i32, true), Chain});
+    SDNode *SetLo = DAG.getMachineNode(
+        (InternalRnd & 1) ? PPC::MTFSB1 : PPC::MTFSB0, Dl, MVT::Other,
+        {DAG.getConstant(31, Dl, MVT::i32, true), SDValue(SetHi, 0)});
+    return SDValue(SetLo, 0);
+  }
+
+  // Use x ^ (~(x >> 1) & 1) to transform LLVM rounding mode to Power format.
+  SDValue One = DAG.getConstant(1, Dl, MVT::i32);
+  SDValue SrcFlag = DAG.getNode(ISD::AND, Dl, MVT::i32, Op.getOperand(1),
+                                DAG.getConstant(3, Dl, MVT::i32));
+  SDValue DstFlag = DAG.getNode(
+      ISD::XOR, Dl, MVT::i32, SrcFlag,
+      DAG.getNode(ISD::AND, Dl, MVT::i32,
+                  DAG.getNOT(Dl,
+                             DAG.getNode(ISD::SRL, Dl, MVT::i32, SrcFlag, One),
+                             MVT::i32),
+                  One));
+  // For Power9, there's faster mffscrn, and we don't need to read FPSCR
+  SDValue MFFS;
+  if (!Subtarget.isISA3_0()) {
+    MFFS = DAG.getNode(PPCISD::MFFS, Dl, {MVT::f64, MVT::Other}, Chain);
+    Chain = MFFS.getValue(1);
+  }
+  SDValue NewFPSCR;
+  if (Subtarget.isPPC64()) {
+    if (Subtarget.isISA3_0()) {
+      NewFPSCR = DAG.getAnyExtOrTrunc(DstFlag, Dl, MVT::i64);
+    } else {
+      // Set the last two bits (rounding mode) of bitcasted FPSCR.
+      SDNode *InsertRN = DAG.getMachineNode(
+          PPC::RLDIMI, Dl, MVT::i64,
+          {DAG.getNode(ISD::BITCAST, Dl, MVT::i64, MFFS),
+           DAG.getNode(ISD::ZERO_EXTEND, Dl, MVT::i64, DstFlag),
+           DAG.getTargetConstant(0, Dl, MVT::i32),
+           DAG.getTargetConstant(62, Dl, MVT::i32)});
+      NewFPSCR = SDValue(InsertRN, 0);
+    }
+    NewFPSCR = DAG.getNode(ISD::BITCAST, Dl, MVT::f64, NewFPSCR);
+  } else {
+    // In 32-bit mode, store f64, load and update the lower half.
+    int SSFI = MF.getFrameInfo().CreateStackObject(8, Align(8), false);
+    SDValue StackSlot = DAG.getFrameIndex(SSFI, PtrVT);
+    SDValue Addr = Subtarget.isLittleEndian()
+                       ? StackSlot
+                       : DAG.getNode(ISD::ADD, Dl, PtrVT, StackSlot,
+                                     DAG.getConstant(4, Dl, PtrVT));
+    if (Subtarget.isISA3_0()) {
+      Chain = DAG.getStore(Chain, Dl, DstFlag, Addr, MachinePointerInfo());
+    } else {
+      Chain = DAG.getStore(Chain, Dl, MFFS, StackSlot, MachinePointerInfo());
+      SDValue Tmp =
+          DAG.getLoad(MVT::i32, Dl, Chain, Addr, MachinePointerInfo());
+      Chain = Tmp.getValue(1);
+      Tmp = SDValue(DAG.getMachineNode(
+                        PPC::RLWIMI, Dl, MVT::i32,
+                        {Tmp, DstFlag, DAG.getTargetConstant(0, Dl, MVT::i32),
+                         DAG.getTargetConstant(30, Dl, MVT::i32),
+                         DAG.getTargetConstant(31, Dl, MVT::i32)}),
+                    0);
+      Chain = DAG.getStore(Chain, Dl, Tmp, Addr, MachinePointerInfo());
+    }
+    NewFPSCR =
+        DAG.getLoad(MVT::f64, Dl, Chain, StackSlot, MachinePointerInfo());
+    Chain = NewFPSCR.getValue(1);
+  }
+  if (Subtarget.isISA3_0())
+    return SDValue(DAG.getMachineNode(PPC::MFFSCRN, Dl, {MVT::f64, MVT::Other},
+                                      {NewFPSCR, Chain}),
+                   1);
+  SDValue Zero = DAG.getConstant(0, Dl, MVT::i32, true);
+  SDNode *MTFSF = DAG.getMachineNode(
+      PPC::MTFSF, Dl, MVT::Other,
+      {DAG.getConstant(255, Dl, MVT::i32, true), NewFPSCR, Zero, Zero, Chain});
+  return SDValue(MTFSF, 0);
+}
+
 SDValue PPCTargetLowering::LowerGET_ROUNDING(SDValue Op,
                                              SelectionDAG &DAG) const {
   SDLoc dl(Op);
@@ -11921,6 +12018,8 @@ SDValue PPCTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::UINT_TO_FP:
   case ISD::SINT_TO_FP:         return LowerINT_TO_FP(Op, DAG);
   case ISD::GET_ROUNDING:       return LowerGET_ROUNDING(Op, DAG);
+  case ISD::SET_ROUNDING:
+    return LowerSET_ROUNDING(Op, DAG);
 
   // Lower 64-bit shifts.
   case ISD::SHL_PARTS:          return LowerSHL_PARTS(Op, DAG);

llvm/lib/Target/PowerPC/PPCISelLowering.h

@@ -1296,6 +1296,7 @@ namespace llvm {
                            const SDLoc &dl) const;
     SDValue LowerINT_TO_FP(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerGET_ROUNDING(SDValue Op, SelectionDAG &DAG) const;
+    SDValue LowerSET_ROUNDING(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSHL_PARTS(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSRL_PARTS(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSRA_PARTS(SDValue Op, SelectionDAG &DAG) const;