1 files changed, 61 insertions, 31 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
index e094981a191..3c8f63e46bc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
@@ -642,48 +642,78 @@ SDValue DAGTypeLegalizer::PromoteIntRes_Overflow(SDNode *N) {
 }
 
 SDValue DAGTypeLegalizer::PromoteIntRes_ADDSUBSAT(SDNode *N) {
-  // For promoting iN -> iM, this can be expanded by
-  // 1. ANY_EXTEND iN to iM
-  // 2. SHL by M-N
-  // 3. [US][ADD|SUB]SAT
-  // 4. L/ASHR by M-N
+  // If the promoted type is legal, we can convert this to:
+  //   1. ANY_EXTEND iN to iM
+  //   2. SHL by M-N
+  //   3. [US][ADD|SUB]SAT
+  //   4. L/ASHR by M-N
+  // Else it is more efficient to convert this to a min and a max
+  // operation in the higher precision arithmetic.
   SDLoc dl(N);
   SDValue Op1 = N->getOperand(0);
   SDValue Op2 = N->getOperand(1);
   unsigned OldBits = Op1.getScalarValueSizeInBits();
 
   unsigned Opcode = N->getOpcode();
-  unsigned ShiftOp;
-  switch (Opcode) {
-  case ISD::SADDSAT:
-  case ISD::SSUBSAT:
-    ShiftOp = ISD::SRA;
-    break;
-  case ISD::UADDSAT:
-  case ISD::USUBSAT:
-    ShiftOp = ISD::SRL;
-    break;
-  default:
-    llvm_unreachable("Expected opcode to be signed or unsigned saturation "
-                     "addition or subtraction");
-  }
 
   SDValue Op1Promoted = GetPromotedInteger(Op1);
   SDValue Op2Promoted = GetPromotedInteger(Op2);
-
   EVT PromotedType = Op1Promoted.getValueType();
   unsigned NewBits = PromotedType.getScalarSizeInBits();
-  unsigned SHLAmount = NewBits - OldBits;
-  EVT SHVT = TLI.getShiftAmountTy(PromotedType, DAG.getDataLayout());
-  SDValue ShiftAmount = DAG.getConstant(SHLAmount, dl, SHVT);
-  Op1Promoted =
-      DAG.getNode(ISD::SHL, dl, PromotedType, Op1Promoted, ShiftAmount);
-  Op2Promoted =
-      DAG.getNode(ISD::SHL, dl, PromotedType, Op2Promoted, ShiftAmount);
-
-  SDValue Result =
-      DAG.getNode(Opcode, dl, PromotedType, Op1Promoted, Op2Promoted);
-  return DAG.getNode(ShiftOp, dl, PromotedType, Result, ShiftAmount);
+
+  if (TLI.isOperationLegalOrCustom(Opcode, PromotedType)) {
+    unsigned ShiftOp;
+    switch (Opcode) {
+    case ISD::SADDSAT:
+    case ISD::SSUBSAT:
+      ShiftOp = ISD::SRA;
+      break;
+    case ISD::UADDSAT:
+    case ISD::USUBSAT:
+      ShiftOp = ISD::SRL;
+      break;
+    default:
+      llvm_unreachable("Expected opcode to be signed or unsigned saturation "
+                       "addition or subtraction");
+    }
+
+    unsigned SHLAmount = NewBits - OldBits;
+    EVT SHVT = TLI.getShiftAmountTy(PromotedType, DAG.getDataLayout());
+    SDValue ShiftAmount = DAG.getConstant(SHLAmount, dl, SHVT);
+    Op1Promoted =
+        DAG.getNode(ISD::SHL, dl, PromotedType, Op1Promoted, ShiftAmount);
+    Op2Promoted =
+        DAG.getNode(ISD::SHL, dl, PromotedType, Op2Promoted, ShiftAmount);
+
+    SDValue Result =
+        DAG.getNode(Opcode, dl, PromotedType, Op1Promoted, Op2Promoted);
+    return DAG.getNode(ShiftOp, dl, PromotedType, Result, ShiftAmount);
+  } else {
+    if (Opcode == ISD::USUBSAT) {
+      SDValue Max =
+          DAG.getNode(ISD::UMAX, dl, PromotedType, Op1Promoted, Op2Promoted);
+      return DAG.getNode(ISD::SUB, dl, PromotedType, Max, Op2Promoted);
+    }
+
+    if (Opcode == ISD::UADDSAT) {
+      APInt MaxVal = APInt::getAllOnesValue(OldBits).zext(NewBits);
+      SDValue SatMax = DAG.getConstant(MaxVal, dl, PromotedType);
+      SDValue Add =
+          DAG.getNode(ISD::ADD, dl, PromotedType, Op1Promoted, Op2Promoted);
+      return DAG.getNode(ISD::UMIN, dl, PromotedType, Add, SatMax);
+    }
+
+    unsigned AddOp = Opcode == ISD::SADDSAT ? ISD::ADD : ISD::SUB;
+    APInt MinVal = APInt::getSignedMinValue(OldBits).sext(NewBits);
+    APInt MaxVal = APInt::getSignedMaxValue(OldBits).sext(NewBits);
+    SDValue SatMin = DAG.getConstant(MinVal, dl, PromotedType);
+    SDValue SatMax = DAG.getConstant(MaxVal, dl, PromotedType);
+    SDValue Result =
+        DAG.getNode(AddOp, dl, PromotedType, Op1Promoted, Op2Promoted);
+    Result = DAG.getNode(ISD::SMIN, dl, PromotedType, Result, SatMax);
+    Result = DAG.getNode(ISD::SMAX, dl, PromotedType, Result, SatMin);
+    return Result;
+  }
 }
 
 SDValue DAGTypeLegalizer::PromoteIntRes_MULFIX(SDNode *N) {